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ALASKA
VOLUME III
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FRONTISPIECE
H.A.E. VOL.|
John Andrew & Son.
Bryn MawrR GLACIER
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SMITHSONIAN INSTITUTION
HARRIMAN ALASKA SERIES
VOLUME Iil
GLACIERS AND GLACIATION
BY
GROVE KARL GILBERT
CITY OF WASHINGTON PUBLISHED BY THE SMITHSONIAN INSTITUTION
1910
ADVERTISEMENT.
The publication of the series of volumes on the Harriman Alaska Expedition of 1899, heretofore pri- vately printed, has been transferred to the Smithsonian — Institution by Mrs. Edward H. Harriman, and the work will hereafter be known as the Harriman Alaska Series of the Smithsonian Institution.
The remainder of the edition of Volumes I to V, and VIII to XIII, as also Volumes VI and VII in preparation, together with any additional volumes that may hereafter appear, will bear special Smithsonian
title pages.
SMITHSONIAN INSTITUTION, WaAsHINGTON, D.C., Juty, 1910
HARRIMAN ALASKA EXPEDITION WITH COOPERATION OF WASHINGTON ACADEMY OF SCIENCES
ALASKA
VOLUME III
GLACIERS AND GLACIATION
BY GROVE KARL GILBERT
NEW YORK DOUBLEDAY, PAGE & COMPANY
1904
CopPpyYRIGHT, 1904,
BY
EpwWARD H. HARRIMAN,
PREFACE
THE present account of Alaska Glaciers, by G. K. Gil- bert, forms the third of the Harriman Alaska Expedition volumes and the first of the technical series. It is based on observations made by the author in the summer of 1899, while a member of the Expedition, supplemented by information and photographs from various sources, and is illustrated by 106 text figures and 18 plates. The vol- umes on Geology, Cryptogamic Botany, Insects and Crus- taceans are to appear simultaneously with it. The vol- umes on Nemerteans, Oligochetes, and several other groups of Invertebrates, are ready for the press, and will follow as soon as they can be printed. The two volumes on Phanerogams, or flowering plants, are expected to ap- pear early in the year 1904.
Acknowledgments are due the Canadian International Boundary Commission, the United States Biological Sur- vey, and, especially, the United States Geological Survey, for the use of photographs and other illustrative material. The editor wishes also to express his appreciation of the drawings prepared for this volume by Mr. W. E. Spader and Mrs. Louise M. Keeler. The frontispiece, plate x1, and a large number of the text figures are by Mr. Spader, while all of the chapter headings are by Mrs. Keeler.
C. Hart MERRIAM, LFtditor.
WASHINGTON, D. C., May 1, 190}.
(v)
CONTENTS
PAGE.
MORTON spss ain coe ne cgoase ras pas seu ionssietes Ss cule tater tes esenkevens I PWN Bag ei sis yous s cdus npces sks days gon cepeds¥endbavaneesvansteess 3 RUA TIUN ens fc catc cn eauo Aas ecu rahicdnaay ie sa nae beanie hea bweeh oes 4 COSA eR BE Revi GLACIERS 65: iocss js natasisjenavsiuserssenuenes i SR ERE SL IPEREE NOD yas oedn sx skssnaaers chee sededtannwesdehe cases chess 7 RAR gus cap inncana gan toneuaveds nesses tan an eearogs desias candguepease II CONSTR SOR coer soo eee aeons dbs cans ca sucneuwac ned cuxeincnvetans 16 DLE RR UMCMCR A iesic cs rcntenecastenso uss Pattpedes cone canseseevascuen suk 20 PACS TUK 5 adindacn ae pedsse vest pidewisienckaeds yanvenie bealeana tess 25 SOE ica Pas Sen laks Abd Soisednn$ chdsnWawnd ke seer esiutess snes eae tesses 33 RAVUIY. FRE, SIMON oon 6s oh l via pens dash eenicks sa snescrneiicee sess 34 RDRMERE AVON chasis va snuconearvinssedessusts yaar eeceutia conte 38
DM SMUG ARACIEE Sits dcsasvncesscosgue daneavaunciewentasy Sineesinenre 39 MAM TIO io sas cccen ssc paree tsa neisacnssnatencacceetiadeskasuovuress 45 BERMUDA: CSENCRED Ge socks ccs ap «son dn sundaes end usnceahotevsesinnse 52 PRIA ANCE yoa 5 cei co oe casas sk okie sea cuswasentnns 44 ccheseeds 58 REE OLE CRIN CION Fs ied oan as buy vp vacua we Soa Roose beets 63
Pe NIE EA MCIOR diss nay ceca ch Sasnces ev ceexwasevscssecovsieusonens ate 66 WWE PURI eit esG ky cl eh his iaies sans dcr eabariaasa ceee ti eeies 69 GSI: COMMONER: fo cer oc cecsyenutsanssaeetaarcnanerssahaavacueeee ss 71 RONCG TNE hin cae vedainsoidaanceisnine eas dese ee sabaaerreieeauiaaer: 81 PRGEINADS COT cs Se eee caw scr cacwag scp nonaecategecaneescenteence 89 CRE, CINCIOE oa ca cunis vcs ocenn ses goneeachecedocesecphertesets nee £07 PUMINIALY OF THOETE CORNICE 555 icscen crscsecscsess veces enseessy sess 102 GOES cg r4c5 sons dd av onsees tives setae tan casney LeeehadenRaacesseesen 106 CHAPTER II.—PLEISTOCENE GLACIATION .......csccscscscsosssccecees pe BEAUGIO V BUCS. 6 linicc cs ddncscncseceasaa vores besseutivas eos panceens tes 114 MIRC OL TIAN VASGA IONS 65055 ston cecceg a caaneecdriacesecn ease 119 PPS-PICLOCENG TODORTAN IY oo ooo ts wen cs rus cue tcerecn eerenes 122 Ae: PRIS PONG AN cacia race sup tiscae stems snes oe des se 123
LAW POREDIANOS Sa cc cuas son eases cSadevaievelegnieswout cilese 130
Pu NG WEE DSASOAEVEN oasn osc cewesnients sinecamy es teceaeress 134 SOOTY oss ans cose pctuacn. asians parse iasesiaton tence 139
Vill CONTENTS
Cuaprer II.—PLEISTOCENE GLACIATION (continued). ica District of Inland Passages (continued). GlachatiOn | ...6c0.s0sosieecenessn<vanser suns edenaemeeerads ubeseeees 139 Rounding of angles............0..secsssersbuedetonsisezons ans 139 CirQuies ....scdasgsdias cae desapechinn ihe sa ves caeeaoepeemeag nous 141 Fiords and Hanging VatlleyS.......5.0.xescinanpecaeeaessae 142 Inequality of glacial erosion, ....:....:iedvadbeyseasesenes 159 Glacial dé posite... cs.cs<isacacdscacaussenesvaremeaygenststes 161 Associated sea-levels.. ...6s5:.ivs.sicnsotbeacesaionmedins 162 High Mountain district. ....5...ssi..ccessesstsespanbeeqenebay tnemrtens 166 Prince William Sound.........<s:<as0ss04¥eedeuh babeubinn cathees aye 173 Kenai Peninsula......0....000-00s.s00sdenevendnateahensmene ope Rienny ein 177 Kadiak Island. .......0.sssecccessesseccsuuy «caus oetnne din eernaenreniens 177 Region of the Gulf Coast....... issccesccavcsnavesbsdb apse tentenees 182 Unalaska Island..,........scsssescassvesteestensewadeutin che leeReeen 185 Bering Sea...... su divewd vvadddaweadey sei r0asanes ewe cat oahe een anne 186 CuapTER II].—GENERAL CONSIDERATIONS AS TO GLACIERS,.... 195 The surface of @ QIACiel. ....5csccsceevcineaessscangun Ghee semen 196 Evenness as compared to rock floor..........:ccsesseceseeseee 196 TLAtePAL Cll ys cos ocr ce cu evans haecdeccndatauh tanya beeanscaeenmeanem 197 Crevasse CY Cle sc. iicc cores doves var vonessshcanvaneenes ane 198 Glacial ect prune ci 5, ccckiva svensavsccanacecstetnrtsdotnescceuvapeen 203 Pressure and erosive power of Tidal Sica csaseeansuaaapaue 210 Rivers of ice and. Gf waters, 0. 025 .ues sve pesswransavenvanneeee 218 Resemp lances o.60. 5) is. acsiies Saasu se cecaqu seus tacaaus pave saeee 218 DOT ETENCEs tage aie anes nate ce rans aalsaassceuee ou tes av aaa e eee ete ee 220
FOO OT ANDY y
Lol
ILLUSTRATIONS
PLATES PLATE PAGE Sy <P See DE A HIACIOL sh asvavan cr cudtasedeccss asubsceudeots Frontispiece i... Map of Alaska, showing route.......12..:..ccsssebssactacsucte I RAE. BAUS PUGUCE ASIACIOR a sis soinvsewaavscrcendbvepabvapsordvesstaees 36 BM x, PARI | EEPROM NTTRONET «ins cvecsandsuvadsnsvsvisberv ence oeeuy 52 FE 5 PN ised ed San ang bien 5 capa diipecarainh inde easel concesiee 54 VI. Profile of Hidden Glacier. Section of moraine............ 56 Wil. Mag.ok Tanstak SIAGer, 00s ccespsicscennessecsvcssscnsvedeasave 58 VIII. Map of Hubbard and Turner glaciers...................00008 62 IX. Panoramas of Hubbard and Columbia glaciers............. 64. x. Turner Glacier in 1591 ahd in 1890........sccssccsconescccces 66 Pak, BES OF Cotte GIA Chel, 6 i. nce se scnsreveseccnesssinvsseess 70 XII. Columbia Glacier, from Heather Island...................... 74 XIII. Maps of Prince William Sound and Port Wells............ 80 AIV. Amherst and Crescent giaciers..........cccsecsscscossecsesscces 82 POT RAEN OME Cis saint waonisdchaans s'seedeoeeiueninends'nédie> Kaien 94 AVI. A hanging valley, Fraser Reach.........ccccssesecessccssecese 116 XVII. Lowlands near Wrangell and Sitka...............ccecseeseeees 132 XVIII. Glaciated rocks.,...... Rian sabeeapnasnavensas ta skuadanns¢esyaesats 206
TEXT FIGURES
FIGURE PAGE « Distribution of glaciers if Alasikn.. 0... .....ccccsccccccscscscccces 8 Davidson Glacier, from periinetala.s io. iisi.c.c.cccccccccssesesees 12 Davidson Glacier, froni above... .cccidicserccvcesccsses seesancants 13 SPEVIGSOR: GFIACIEL, SIDE VIOW 05 sciscesawssvorercarnessarsiccscevcseres 14 DOREY OF IIACUIGOR NEAT os sac asesnciens vovendeestantsesncisd Coeatene 15 Longitudinal section of Davidson Glacier...................0000e 15 Map of Glacier Bay........ anaes aus esuinaiee ha tes See onwanieg aeuarioues 18 Remnant glacier south of Hugh Miller Inlet..................... 20 DIELS RSRON Sha ch tuhs oc caus Spnseanauics cient ee aad evs anateseeeisass 20 pa ER UIE PEON ais ses pa cg be scagnseseccusancstesnsescetesctsanes 21 OED OE SEOEE SUNDEE Fn Cyc tigu ack svar Vecouess Ua ieksea yee evencenes 27
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x ILLUSTRATIONS
FIGURE PAGE 12. Reid Glacier, from the north.......0c0cac<oveccanaveeaesourabeswanen 28 13. Reid Glacier, from the northeast... 5..,ciisaccneshabeeasancwans 29 14. Reid Glacier, from the north Wert....04.; iccccureocptateeosseumiaben 30 15. Reid Glacier, from the northeast... ..iac.stecsncosn phavanastanaes 31 16. Rock-laden berg’... wcisscinsssosecvetneeiaeansunenceeeniaeninaahtevs 33 17. Map of Hugh Miller: Tite oe cnenscascugsnseounvasansauenednenaceve 34 18. Till left by Hugh Miller Glacter ss. ion icc ecseddeatonss rea hece 35 19. Charpentier GIActe? iosis.ssasaceenaidepseseyensandeeamigseeiatess 36 20. La Perouse Glacien, i... .ci.siccpetenacanshowasend demetweiliaaneniateecs 39 21. Map of margin of La Perouse Glacier..................ceseeeeees 40 22. Section of timbered ridge near La Perouse Glacier............ 4I 23. Barren zone at margin of La Perouse Glacier................... 41 24. Push-moraine of La Perouse Glacier..............ssssesscseeeees 42 25. La Perouse Glacier; contact with forest.............ssssecesesees 43 26. Map of Yakutat Bay -..5..0..+,.ssosciousssesvanneosignebsaranaoniaeeete 46 27. Map of Yakutat Bay, showing configuration of bottom...... 50 28. Hidden Glacier......csisersscccssscsetesesecesnseh)saaueniieeeiaameaee 53 a9. Waste plain of Hidden Glacier............c..sssesedsaskebananeneel 57 30. Westward from Nunatak Glacier... ....5..0s:0.jccseenyanvaaewns 59 31. Tidal front of Nunatak Glacier.....c...:,.s:ececsssaeecsnepennrien 60 32. Cascading glacier in Nunatak Fiord................scsscescoseeees 61 33. South tongue of Nunatak Glaciev.........:sscovdvnsensacseubeb nants 61 34. Tidal front of Nunatak Glacier .......55.cc0s cxcenentnsveodasanen 62 45. Hubbard GIacler. ...05.5.0.0scs0ssnesendsecsecess taney veces Gieueoerd aioe 64 36. Longitudinal section of Turner Glacier................ceceeeeeees 68 37. Panorama of Columbia Glacier.. ..........csussvensveadevee tan ves 72 38. Western edge of Columbia Glacier... ..,.....cisevasstnvrenoe ten 76 39. Push-moraine, west shore of Columbia Bay...............see00 77 40. Fluted moraine at edge of Columbia Glacier..............e0006. Y 41. Moraine marking attack by Columbia Glacier on forest...... 79 42. Outlines of Columbia Bay: .....:ccccicsenesiesocasnpes sohommonns 81 43,. East: past of front of Yale Glacier... ....assesscakessnccersmeatiots 83 AAs, Tlarvard GIAcier iiiss.sccdacecvexonsrweccsahasppaceumunkseenesaseesir es 85 AS.. West side of College Pion i.5.< 2 Guvienave biaceonstencuasnac senate 87 46.; Distant view of Batey Glater. 2.05 clcrecsicany we tsnce i nieenreee go Av. PartOr Front. Of TRArey CHAR cals sec nce car ccnencercasivess ov ies gI 40. Caves in frontal cli of Batey (slactet 560. cciscvendciectanseees gI AO; kuast part of front Of Barty S51AClers.ic.25 2.00 rssseeseceencouscpes 92 HOe eTPEMEING CIACIEN 15015 ceten ves assiwasaseasesscaroassaseeadncites ee: 93 S¥s OUurprise and Cataract CiAClete, 665665052 io eansce paasiecnsesades sass 94
ILLUSTRATIONS xi
FIGURE PAGE 52. Hemlocks bordering Harriman Fiord ..............csesseeeeeeeees 97 CBs RAMU SPARC cea rsaxcinverishaceéunss ons onapadtodentdpetgieseont 99 54. South wall of valley at front of Grewingk Glacier............. 100 eo . Lreneeipation OF placier IGCAMGICS ........cicesvsasedornsenscddatean ass 105 56. Diagram illustrating origin of hanging valleys.................. 115 57. Diagram illustrating origin of hanging valleys................4 115 58. Diagram illustrating discordance of hanging valleys........... 116 59. Map; fiords of the Inland Passage district....................645 120 Bee RO Ue RMON COIs ia o5 oss ciceca union ces esds ehewuk us San'vanshepcudececebeeans I2I 61. Upland topography near Cape Spencer,.............ecseeseeesees 125 62. Upland topography near Berner Bay...............sseccsecesesees 127 63. Upland topography near Walker Bay ..............ccsececeeeeeeee 128 ik ANAL CE VOTRE SOLAN, oi das cbs pe tir nescnaiin nae tapecnvedsncenndabens 131 He. Cid penepiain nest BUA s5. 5s cas win loads skencevernsdinevencatines sce 132 hs. Dougias Teland, Fem FuAeAte boi. aces cocdsssabactnesecssatnces seuss 133 fi. A. fiord of the: Inside, Paap... sesocvedesssssescseeeepacesvarsanss I4I Gs) A ford of the Insiibe Passage «........sccscccsasecsevvcvescenseveces 142 69. Hanging valley on Vancouver Island................cccceeeeeeeees 143 70. Hanging valley on Princess Royal Island.....................065 145 Us, sannorne valley, P¥aser Kah, ,...0sccssnescscsecectsececcsvccsnses 146 a, SAamne Walley, F'PAbet FLOR. 5.550eciiswexesecesccscsonsseaeness 146 Sr ROC WEIL GE LAE: TOWN nas cs neces sovenstsewsesccssocesecenetenssns 148 na WO Oe OR SAT TO 56 as 5.05 Ra csnsas ds hesaode ss siassvevescainse 149 TERME AG RMON SMININ S555 50.90, hxs sislsdsddadsboeseedenedepssancersvesias “152 i SUMED GUAGE, “ESIGA ENC s. cccsocncs coc cvossstessscnesesacscrenes 153 oy, ortheast wall of Chilkoot trough..........csscsecsseresosssveosee 154 a: Profile from ‘Taiya Pass south wat ....0.0..cscsccsecsersensecsocss 155 479. Cross-profiles about head of Lynn Canal.................ceseeeee 155 dn PROMS GR: SOO IVER: os crasrecacsavednaeadanesise sack ledvens séaueee 158 Sis SIRS VERO, INMNRAR BION so) ox cin cas saviesvncscsseanscssccnns IVI Dba dN TURE SOA i ies sc ccoaypasandtekeutasincsnpsebeseuacdnaee 174 53; Hinchinbrook Island, from the seac....0i0ds.scsesecsserrssecesens 174 84. Diagram of northwest wall of College Fiord.................... 175 85. Terrace on Spruce Island, opposite Kadiak Island............ 179 SMa DEAMEUG GRE Se PATEM ES Sy ju race Yok gentssRernseunmeaancsenamernenkiGa tetas 180 eta, WADIE ROCRIN Ma MIR VIA IE So sii ceacessed eeae ns Videwsensste'arenns 181 88. Hanging valley near Kadiak village,.........ccecsoovscsscscsessee 181 ma. Acrater s90r oi St. Pant Islas ooo. ss sa coca eseneties tosdngeaice 187 90. Unglaciated knob on St. Matthew Island.....................008 189 gi. Stream-graded valley near Port Clarence ...............sceeeeeee 189
Xil ILLUSTRATIONS FIGURE PAGE 92. East wall of Plover Bay, Siberia.....<..csccovsdanedhan soeadeenanns 190 93. Hanging valley, Plover Bay......0:1s0ssseesspacacupveessewannepangel Ig! 94. Downward limit of crevasses in Muir Glacier.................. 198 95. Crevasses and seracs, Muir Glacier... .c<ccusicigssiisenaenecbene 199 96. Pinnacles on Columbia Glacier.............csesesseseeeeceeceneees 200 97. Back of Columbia Glacier..............sssssesereecnserecsecsseeeres 200 98. Level tract on Muir Glacief..ic.cccciesssacaseisneeayars onagateaiess 201 99. Ideal profile and section of a glacier... 5545 Acssseiiervnenedes 201 100. Ideal section of water-filled crevasses...........ccceeseeeeneceeeees 202 101. Influence of drift on surface character of glacier............... 202 102. Ice sculpture in Russell Fiord,. . i.) .xicdecpasngeds ies eaves 209 103. Diagrams illustrating flotation theory of tidal glaciers........ . 210 104. Diagrams illustrating non-flotation theory of tidal glaciers... 211 105. Contact phenomena of glass and mercury............sceseseseees 212 106. Ideal section of tidal glaciet...............:isseskseeage banana 215
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GLACIERS AND GLACIATION BY GROVE KARL GILBERT
INTRODUCTION
THE glaciers of Alaska are many and the district through which they are distributed is large. The region formerly overrun by them is still larger. Ten years ago Russell and Kerr surveyed and studied Malaspina Glacier and its dependencies, and about the same time Reid made a scientific survey of Glacier Bay and its bordering glaciers; but these two tracts are only dots on the general map. All other glacial studies in the great field have been of the nature of reconnaissance and most of them have been carried on incidentally in connection with general geographic or geologic work. The Harriman Expedition added one more to the list of reconnaissances.
Until recently observations have been limited to the coast and it is still true that the greater number of glaciers which have been studied or mapped are coastal, or at least visible from the sea; but at the present time interior gla- ciers are receiving more attention, and knowledge of them is rapidly growing. Geographic investigation, so long as
(1)
2 ALASKA GLACIERS
stimulated by only the fur and salmon industries, was di- rected chiefly to coastal regions, but the development of gold placers turned attention to the interior, and for sev- eral years the topographers and geologists of the United States Geological Survey have been actively engaged in the exploration and survey of inland districts.
The growth of knowledge of Alaska glaciers is so rapid that a summary of existing knowledge would have but transient value. Generalization as to most points of world- wide interest is at present impracticable because observers have differed widely in their preconceptions and criteria, and the data consequently are not homogeneous. It has seemed best, therefore, to make the present report pri- marily a record of the data gathered by the Harriman Ex- pedition and to make use of other material only when it is closely connected with the new data or is otherwise ser- viceable in their interpretation.
Regarded as a reconnaissance of glacial geology, the cruise of the ‘ Elder’ was fairly comprehensive. It not only covered rapidly a wide extent of coast but it brought under view a great variety of phenomena. The general impressions acquired while the ship was skirting the coast were supplemented by the results of more definite and detailed observation at a few points on the land; and the impressions,acquired by local studies of individual glaciers were enlarged by the panoramic view of many others. Opportunities for close examination included landings from the ship at thirty-four localities, at three of which the use of a camping outfit extended the time to several days. ‘The remainder of the two months covered by the voyage was spent on the ship, and about half the sailing time was so conditioned by distance from shore, by light, and by weather, as to permit profitable observation of the coast. After the voyage was over physiographic studies were continued by the aid of photographs. Thousands of
INTRODUCTION 3
views by members of the Expedition were examined, as well as a large number from other sources, and at least several hundred of these have yielded information as to glaciers and glaciation.
In arranging the material for presentation it has been found convenient to make an arbitrary division of the history of glaciation, connecting such changes as appear to have occurred within a few hundred years with the ex- isting status, and classing all remoter changes with the geologic or Pleistocene series. This procedure is a matter of convenience only; it is not determined by a turning point in glacial history, but by a difference in the nature of the evidence by which the history is recorded. The direct observational record, for a few localities, reaches back a little more than a century, and inference from the age of trees extends a little farther; but for all earlier times the data are purely geologic and the changes have not been measured in years.
Under this classification the heads of my principal chap- ters are Existing Glaciers and Pleistocene Glaciation. The changing relations of sea and land also receive atten- tion, but these are so closely connected with the problems of Pleistocene glaciation that they have not been given a separate place. Notes of a general character as to glaciers and their work are in part introduced along with local descriptions and in part assembled in a closing chapter.
Route.— Through the greater part of the journey I re- mained with the main party, so that the red line on the route map (pl. 1) shows my course with approximate accuracy. It seems necessary to mention here only a few deviations and details. Such dates as are of importance are noted in connection with the descriptions of individual glaciers.
In Glacier Bay I spent a day and a half at Muir Gla- cier, and then, with Muir and Palache, visited Hugh Miller,
4 ALASKA GLACIERS
Reid and Geikie inlets in a rowboat. This excursion oc- cupied four days, three camps being made on the shores of the bay.
In Yakutat Bay I landed at Hidden and Nunatak gla- ciers and at the summer village of the Yakutat Indians. Two days were spent, with Muir, Gannett, and Kearney, in a boat excursion which visited Hubbard Glacier and Osier and Haenke islands.
In Prince William Sound I touched at Orca, and was then left at Columbia Glacier with a boat and shore party, including Palache, Coville, and Curtis, while the ship ex- plored Port Wells. We remained three days, and after- ward had a partial view of Harriman Fiord.
In Cook Inlet I was landed for a half day at Grewingk Glacier, while the ship made an excursion up the main bay.
I was with the ship on all routes about Kadiak Island, landed briefly on the western coast, spent several days at and near Kadiak village, and visited Long Island.
At Port Clarence I was of a party that crossed the bay in a launch and visited the mainland.
Photographs.— For the study of changes in the size of glaciers photographic views are of peculiar value. A view showing a glacier or part of a glacier in relation to details of adjacent land constitutes a record which can at any time be compared either with the objects themselves or with another photograph made in another year or month. That a photograph may have its highest value for such use its date must be known, including year, month, and day of month. The Harriman Expedition carried many cameras and secured a large number of views of glaciers. Some of these views are reproduced in the present and preceding volumes, and are thus made available for the investigator. So far as they are contained in this volume, their dates are given in the associated text.
PHOTOGRAPHS 5
The geographer who shall undertake in the future to study the variation of Alaska glaciers will have use not only for the fuller details of the original photographs but for a more complete series, and the following information is given for his benefit.
Of the many series of photographs made by the mem- bers of the Expedition, three may be regarded as public, and these also contain the most important records of the glaciers. Mr. E. S. Curtis, the official photographer of the Expedition, made the largest and best views, and keeps them on sale at his photographic establishment in Seattle, Washington. The negatives made by Dr. C. Hart Mer- riam are filed at the office of the Biological Survey, U. S. Department of Agriculture, Washington, D.C. My own negatives are filed at the office of the U. S. Geological Survey, Washington, D. C., where a set of prints may be seen and prints from negatives may be ordered.
The dates of our photographs for the several glaciers are as follows, the year 1899 being understood in each case: Amherst, June 26; Barry, June 26-29; Bryn Mawr, June 26; Cataract, June 27; Charpentier, June 11; Colum- bia, June 25-28; Crescent, June 26; Crillon, July 24; Davidson, June 6; Grand Pacific, June 12; Grewingk, July 21; Harriman, June 27; Harvard, June 26; Hidden, June 20; Hubbard, June 19-22; Hugh Miller, June 11; Johns Hopkins, June 12; La Perouse (near views), June 18; La Perouse (distant views), June 18 and July 24; Muir, June 8-13; Nunatak, June 20; Radcliffe, June 26; Reid, June 12; Roaring, June 27; Serpentine, June 26-27; Smith, June 26; Surprise, June 27; Turner, June 19-22; Vassar, June 26; Wellesley, June 26; Yale, June 26.
The table on page 6, giving series and negative num- bers of photographs from which text figures were made, includes most of the figures based on photographic views. Information as to others is given in their labels and other
6 ALASKA GLACIERS
associated text. ‘Titles of series are abbreviated in the table as follows: ESC=E. S. Curtis, Seattle, Wash.; USGS = U. S. Geological Survey, Gilbert; USBS =U. S. Biological Survey, Merriam, 1899; CBC = Canadian Boundary Commission, Ottawa, Canada. The Boundary Commission photographs are mounted in an album of many volumes, and the complete reference includes num- ber, volume and page. <A copy of this album is in the library of the State Department at Washington.
SOURCES OF PHOTOGRAPHIC MATERIAL USED IN TEXT FIGURES.
Figure. Series. Negative or Photo. Figure. Series. Negative or Photo. 2 CBC 3, ¥. 32,9: 5 54 USGS 456 3 CBC 117, V. 12, p. 43 61 CBC | 93-4, Vv. 14, p. 53 USGS 247 62 CBC 96, v. II, p. 30 § USGS 282 63 CBC | 132-3, v. 8A, p. 50 9 USGS 270 64. USGS 222 12 CBC » Ve 14, Pp. 13 65 USGS 324 13 CBC 38, V. 14, p. 11 66 USGS 470-471 14 USGS 259-261 67 USBS 293 15 USGS 257-258 68 USBS 55 16 USGS 276 70 USBS 250 18 USGS 281 71 USBS 292 19 USGS 263 72 USBS 251 20 USGS 467 73 USGS 221 23 USGS 334 74 CBC | 109A, Vv. 12, p. 81 2 USGS 333 75 CBC 93-4; V- 12, p. 3 2 USGS | = 365-366 76 USBS 29 USGS 367 77 CBC 68, v. 12, p. 42 30 ESC 259A 80 CBC 93, V- 6, p. 43 31 USGS 305 81 USGS 373 32 USGS 302 82 USBS 94 33 USGS 307 83 USGS 383 34 ESC 259 85 USGS go 35 USGS 298-299 86 USGS er 400 38 USGS 355 87 USGS 392 39 USGS 356 88 USGS 402 40 USGS 352 go ESC 393 (?) 41 ESC 311 gI USGS 433 43 ESC 275 g2 USGS 430 45 USBS 117 93 USGS 443 46 USBS 137 96 USGS 346 49 ESC 280 97 ESC 304. 50 USBS I51 102 CBC 3, V- 17, p. 3. 53 USGS 454-455
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CHAPTER I
EXISTING GLACIERS
GENERAL DISTRIBUTION
NEaRLy all the glaciers of Alaska are comprised within a belt of moderate width which follows the southern coast from the Aleutian Islands to Portland Canal (see fig. 1). Curving about the great bight of the Pacific Ocean known as the Gulf of Alaska, this belt has a length of 1,600 miles, and its extreme width, near the middle, is about 250 miles. Within it the arrangement of glaciers is irregular, but their more important groups occupy the middle region, while near the ends they are comparatively sparse and small.
The explanation of this massing of glaciers along the southern coast is not far to seek. The general circulation of the Pacific Ocean brings to the Gulf of Alaska a cur- rent of water which has been warmed in the tropics and still retains so much heat that its mean temperature is considerably above the normal for the latitude. The ocean is therefore, at most seasons, warmer than the con- tiguous land, and though air currents passing from ocean to land convey heat to the land they are themselves cooled.
(7)
8 ALASKA GLACIERS
While traversing the ocean the air becomes loaded with moisture, the cooling over the land diminishes its water- carrying capacity, and part of its load falls to the ground as rainor snow. Moreover, all this coast is mountainous, so that landward flowing air is compelled to rise, and its capac- ity is still further reduced by rarefaction. At the greater altitudes the ratio of snow to rain is comparatively large,
" 158° 154" 150° 146° 142” 128° 134°
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FIG. I. DISTRIBUTION OF GLACIERS IN ALASKA.
The belt containing glaciers is shaded by parallel lines.
and the mountains thus become gathering grounds for the snows that feed glaciers. Farther inland the air currents descend somewhat and the precipitation is diminished until the conditions for glacier formation cease. Hayes states that while the névé line of glaciers on the southward face of the St. Elias Alps lies at about 2,000 feet above sea- level, its altitude on the northern face is over 6,000 feet.’
1An Expedition through the Yukon district. By Charles Willard Hayes. Nat. Geog. Mag., vol. Iv, p. 153, 1892.
DISTRIBUTION OF GLACIERS 9
Along the western coast of Alaska the conditions are different. Bering Sea lies practically outside the influence of the Pacific circulation and the temperature of its water is approximately normal. Its power to charge air cur- rents with moisture is small, especially in winter; and though the winter temperature over the adjacent land is low, the snowfall is not heavy. There are no great moun- tain ranges to concentrate the precipitation, and the snow of winter, being broadly spread over plains or caught by ranges of moderate height, is dissipated by the melting and evaporation of summer.
The glacier-bearing belt includes about three-tenths of the vast territory of Alaska. Its exploration has but begun, yet enough is known to give it rank as the third great glacier district of the world, only the Antarctic con- tinent and Greenland surpassing it. Its ice may be roughly estimated to occupy a tenth of the surface, or an absolute area of between 15,000 and 20,000 square miles, and this expanse is so divided and scattered as to offer to the student the utmost variety of local condition and de- tail. Of alpine glaciers, such as would receive individual names if near the homes of men, there are many hundreds, possibly more than a thousand; of broad, composite fields, like the Muir and Malaspina, there are about a half dozen; and more than thirty are known to reach the coast and cast bergs into the sea.
Skirting the land in a ship and making only brief ex- cursions away from it, we saw only glaciers of the coastal mountains and lowlands, and close inspection was limited to the lower ends of ice streams. The phenomena which arrested our attention were those of wasting, of the depo- sition of detritus, and of the advance and retreat of the ice fronts. It soon became evident that our chief opportunity to advance glacial science was through contributions to the history of local changes in the frontal boundaries of
Io ALASKA GLACIERS
glaciers. That which was accessible to us had been accessible to our predecessors also, so that at several points we could compare present with past condition ; and, for like reason, whatever record we might make could readily be used by the investigators of the future. Effort was accordingly made to visit as many as possible of the glaciers already described and mapped, and at all points visited to secure an intelligible record of the exist- ing status.
The plural pronoun in the preceding paragraph is not the conventional affectation of modesty, but springs naturally from the consciousness that the facts I am to present were not wholly of my own observation. In grouping the material for publication it seemed to my colleagues in geology, Emerson and Palache, as well | as to myself, that it would be better to classify by sub- jects than by observers, and as glaciers fell to my share, I have absorbed the glacial observations made by these gentlemen. I am greatly indebted also to the map work of Gannett, to the historical data and fertile suggestions of Muir, and to the timely cooperation of Dall and Coville.
Before taking up the description of the glaciers, a few words will be devoted to the terminology connected with their broader classification. The distinction between a/- pine glaciers (sometimes called glaciers proper) and con- tinental glaciers (also called ice-sheets) has long been recognized. Alpine glaciers are fed by névés in high mountains and as rivers of ice descend mountain valleys. Continental glaciers gather on broad plains or plateaus and spread outward. Russell, as a result of studies in Alaska, recognized a third type, the Azedmont.’ A pied- mont glacier is a broad sheet of ice resting on a lowland
1An Expedition to Mount St. Elias, Alaska. By Israel C. Russell. Nat. Geog. Mag., vol. 111, p. 121, 1891.
LYNN CANAL II
at the foot of a mountain range, resembling a continental glacier in its mode of wasting, but distinguished by the fact that it is fed by the alpine glaciers of the mountain. An alpine glacier may be simple and separate, or com- pound. Two or more often descend from the same névé. Still more frequently two meet and coalesce after the manner of rivers, and a trunk glacier may have many tributaries. Small alpine glaciers are sometimes called glacterets, or, if visible high on the sides of mountain valleys, hanging’ glaciers.
For the purpose of the present report it is convenient to distinguish glaciers which reach the sea and discharge bergs, from those which end on the land. Reid calls these, severally, ¢zde-water and alpine glaciers; and they have also been called (after whose initiative I do not know) /¢ve and dead glaciers. Reid’s use of ‘ alpine’ con- flicts with the well-established use already mentioned, and the terms ‘ live’ and ‘ dead’ are clearly misleading, as the great majority of the active glaciers of the world fail to reach the sea. I shall abbreviate ‘ tide-water’ to ¢zdal and employ zon-tidal as its antithesis.
LYNN CANAL
The order in which the glaciers were observed was from east to west, and it has been found convenient to adopt this as the order of description also.
On the islands of southeastern Alaska there are no glaciers, and those of the mainland, south of Juneau, nestle in recesses of the mountains so far from the steamer route that we had only distant glimpses. But in Lynn Canal we followed a great fiord between ranges at once so lofty as to project well above the snow-line and so bold as to ex-
1Glacier Bay and its Glaciers. By Harry Fielding Reid. Sixteenth Ann. Rept.
U.S. Geol. Survey, part 1, 1896. See pp. 429 and 442. The term tide-water was used by Russell as early as 1892. See Am. Geol., vol. rx, p. 322, 1892.
12 ALASKA GLACIERS
hibit their crowning banks of snow and ice in continuous panorama. These ranges have been mapped in some de- tail by the U. S. Coast Survey and the Canadian Inter- national Boundary Commission, and it appears from a comparison of the glaciers with contours of altitude that the snow-line descends in both directions away from the fiord. On the mountain slopes overlooking the water glaciers do not form at a lower height than 4,500 feet, but
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FIG. 2. DAVIDSON GLACIER, FRONT VIEW, 1894.
Showing the trench form of its valley, the spreading of its end, and the two zones of the fringing plain. Photograph by W. Ogilvie, from peninsula at left in fig. 3. See page 6.
on the opposite slopes of the same ranges 3,500 feet seems to be enough.
Davidson Glacier, fed by a high snow-field lying several miles back of the first mountain crest on the west, flows to the fiord through a narrow trench and reaches sea- level, though its ice does not actually touch the water of the ocean. In its mountain trench it has a width of only a half mile, but on escaping from the confining rock walls and entering the fiord it immediately spreads into a semi- circular fan with a radius (in 1894) of about three-fourths of a mile. All about its frontal margin is a fringe of low- land averaging three-fourths of a mile in breadth, consti- tuted, at the surface, of rock waste brought by the glacier.
DAVIDSON GLACIER 13
There may be much unmelted ice beneath the visible gravel, but the lowland certainly contains a great body of gravel which, if glacier and ocean were withdrawn, would appear as a great curved ridge of water-laid moraine stuff. Glacier and moraine together encroach nearly two miles on the water of the fiord— a branch of Lynn Canal called Chilkat Inlet — reducing its width to about one mile.
—
FIG. 3. DAVIDSON GLACIER,
View of terminal fan from the high peak at the right in fig. 2. Shows the barren and forested zones of the fringing plain. The glacier is partly concealed by a rock of the fore- ground. From a photograph by J. J. McArthur, 1894. See page 6.
The depth of the moraine, or moraine-delta, where it occupies the middle of the fiord is more than 500 feet. The profile of the ice fan, as shown by photographs, has a slope of one foot in ten (see fig. 4). The gravel low- land is much flatter, but the submerged face of the deposit descends to the bottom of the fiord with a general rate of one foot in three.
We made no landing here, and our facts are derived chiefly from Russell, who visited the foot of the glacier in 1889; from the Coast Survey chart, based on surveys in 1890-94; and from photographs made by the Canadian
14 ALASKA GLACIERS
Boundary Commission in 1894.1 They are of interest in this connection chiefly from their bearing on the interpre- tation of morainic ridges observed farther west, at the front
oe ww we we ee eee rioae ac te a tt WR ne ais PN eee eee -_- —-
FIG. 4- DAVIDSON GLACIER, Side view of expanded end, June, 1899.
of the Fairweather Range. If Davidson Glacier were to melt away and the sea to retreat from Chilkat Inlet, there would remain in the valley a high ridge of water-laid gravel, recording by its circling course the present out- line of the glacier front, and by its even crest line the present position of the sea surface.
As to modern changes in the extent of this glacier there is little specific information, but the condition of the fring- ing plain warrants a few general statements. An outer zone is covered by forest, an inner is barren (figs. 2, 3 and 5). The forest is in general lofty, dense, and apparently mature, but a narrow belt next the barren zone has smaller trees in rather open growth. The forest zone has an average width of less than half a mile, ranging from one- fourth at the north to five-eighths at the south; the bar-
1See page 6 and figs. 2 and 3.
DAVIDSON GLACIER 15
ren zone in 1894 ranged from one-fourth mile (east side) to nearly one-half mile (north side). There were many lakelets in the barren zone (1894) and a few in the forest,
SOME OT UES
FIG. §. MAP OF LOWER PART OF DAVIDSON GLACIER.
Based on Coast Survey chart 8303 and Boundary Commission photographs made in 1894. The contour interval on land is 500 feet ; under water, 250 feet. Barren lowlands dotted; for- est indicated by stars. and these are probably indicative of the melting of ice buried under the gravel. It seems safe to infer (1) that for centuries (age of the mature forest) the glacier has not exceeded its present extent by more than three- eighths of a mile, and (2) that the period since it last
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FIG. 6, LONGITUDINAL SECTION OF DAVIDSON GLACIER AND CROSS SECTION OF CHILKAT INLET.
£, glacier. m, moraine-delta. w, water of inlet. %, profile of mountain range near glacier.
16 : ALASKA GLACIERS
reached the three-eighth-mile limit is roughly measured by the age of a half-grown forest.
GLACIER BAY
The next depression west of Lynn Canal is broader, as well as more complex in the details of its config- uration, and its general trend is northwestward in- stead of northward. On the west it is separated from the Gulf of Alaska by the Fairweather Range, the dominant mountain mass of this region. Glacier Bay, occupying its main axis, sends many branches into the troughs among “its hills and mountains, and would be still more complicated in outline but for the clog- ging of the valleys by glaciers. Six of its inlets head against ice walls, from which bergs are constantly falling.
The glaciers of this basin are better known to the phys- ical geographer than any others of the Alaska belt, and one of their number, the Muir, enjoys the same preemi- nence in popular acquaintance and appreciation. The group was explored, sketched, and studied by Muir in 1879 and 1880. Wright made.a visit in 1886, producing a rough map and working out the main elements of the later glacial history. Reid, in 1890 and 1892, executed a careful survey of the shores, the lower portions of the tidal glaciers, and a broad inland tract including the greater part of Muir Glacier; developed much further the history of recent changes; and instituted a number of investigations bearing on the physics of glaciers. Minor studies were made by Cushing (1890) and Rus- sell (1890), the map work has been extended by the Canadian Boundary Commission, and a fine series of photographs were made by the Commission in the sum- mer of 1894.
GLACIER BAY 17
To the body of information gathered and published by these investigators* our addition was comparatively unim- portant. The five long days of our stay, though utilized to the utmost and replete with interest, served only fora partial review of the features of the immediate coast. As to the more general aspects of the topography and physical history we verified the work of our predecessors, but we were able to extend it only by bringing down to date the records of changing glacier fronts.
Except near the mouth, the shores of Glacier Bay are treeless, and large tracts are almost destitute of vegetation. A variety of other facts show that this barrenness is due to the recent occupation of the surface by ice, and the ex- tent of the barren zone measures the amount of modern recession of the glaciers. Another series of phenomena, including vestiges of a forest and remnants of a moraine- delta, show that the epoch of expanded glaciers was pre- ceded by an epoch of contracted glaciers when the ice occupied less space than at present. Thus, from a condi- tion of minimum extent, the glaciers grew to a maximum of brief duration and then wasted away to their present dimensions. Vancouver’s narrative seems to show that at the time of his visit to the coast (1794) the ice was near its maximum, and subsequent observations, beginning with those of Muir in 1879, show rapid and nearly continuous retreat. The magnitude of this oscillation is perhaps without parallel in the records of glacial changes within the historic period. During the maximum epoch an ice flood not only filled Glacier Bay for thirty-five or forty miles, but submerged many islands and bordering hills
1John Muir, Cruise of the Corwin in the Arctic Ocean, p. 136, 1884; The Mountains of California, pp. 23-24, 1894. H.F. Reid, Nat. Geog. Mag., vol. Iv, 1892; Sixteenth Ann. Rept. U. S. Geol. Survey, part 1, 1896. H.P. Cushing, Am. Geol., October, 1891. G. F. Wright, Am. Jour. Sci., Jan., 1887; The Ice Age in North America; Man and the Glacial Period. I. C. Russell, Am. Geol., March, 1892.
18 ALASKA GLACIERS
from 1,000 to 2,000 feet in height and reduced the lesser mountains of the basin to the condition of projecting peaks, or nunataks. The sea front made a continuous ice cliff ten miles long. Then the great trunk glacier gradually wasted; therounded crests of submerged hills began to reap- pear as nunataks; rows of nunataks coalesced into mountain ranges; the ice cliff retreated up the bay, passing one nunatak after another and leaving it as an island or a promontory; one by one the tributary ice streams were aban- doned by the waning trunk and left as in- dependent glaciers, whose terminal ice FIG. 7. MAP OF GLACIER BAY. cliffs retreated erad-
Ruled areas, land. SG, Brady Glacier. CG, Char- ° pentier Glacier. GJ, Geikie Inlet. GP, Grand Pacific ually up their several
Glacier. H/, Hugh Miller Inlet. HM, Hugh Miller sea arms. These Glacier. H, Johns Hopkins Glacier. MJ, Muir Inlet. : L MG, Muir Glacier. Q, Queen Inlet. R, Rendu Inlet. modifications of the
RI, Reid Inlet. W, Willoughby Island.
coastal geography were accompanied by equally remarkable changes at higher levels. Several glaciers lost their névés, by dis- sipation or by diversion, and being thus deprived of nourishment and of part of their propelling force, lie nearly stagnant and are slowly melting away. A num- ber of fragments of ice streams are stranded on flat passes among the hills, where they lie almost inert but
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GLACIER BAY 19
with slow movement on two sides in opposite directions, part of the mass tending backward toward its original source.
Of the abundant evidence from which this history was worked out by my: predecessors* I saw only a small frac- tion, but enough to substantiate their conclusions in all essential respects. I skirted the barren coasts over which vegetation is slowly creeping from the south. I saw glacial till and gravel charged with bruised trunks and boughs from the ancient forest. I saw the bare ice-carved hills, still retaining striz and polish under a climate that has obliterated from most exposed surfaces the similar records of Pleistocene glaciation (pl. xvi). I saw the banks of stratified gravel before Muir Glacier — remnants of the old moraine-delta— and noted that their upper surface had been first sculptured by the readvancing glacier and then sheeted with till during the subsequent retreat. And I saw a remnant of the ice flood stranded on a saddle a thousand feet above tide.
The saddle to which I refer is part of a small trough extending southeast from Hugh Miller Inlet and lying parallel to the adjacent great trough of Glacier Bay. During the recent ice maximum an ice current followed this trough from northwest to southeast, and when the supply from the northwest finally ceased and this strand of ice had nothing to urge it except its own weight, its ends slid into neighboring valleys, but the central part lay balanced on the summit and became stagnant (fig. 8). The adjacent hills are too low to furnish the snow needed to replenish its annual loss by melting, and so it is slowly wasting away
1Wright, Am. Jour. Sci., 3d series, vol. xxxu1, pp. 11-18, 1887; Ice Age, pp- 55-62, 1889. Reid, Bull. Geol. Soc. Am., vol. 4, pp. 32-41, 1893; Sixteenth
Ann. Rept. U. S. Geol. Survey, Part 1, pp. 434-442, 1896. Cushing, Am. Geol., vol, VIII, pp. 214-224, 1891.
20 ALASKA GLACIERS
Of the existing glaciers of the basin ten are now tidal. We visited the Muir, Reid, and Hugh Miller. To the Grand Pacific, Johns Hopkins, and Charpentier we ap- proached so near as to obtain some information as to re-
FIG. 8. REMNANT GLACIER SOUTH OF HUGH MILLER INLET, FROM A PENINSULA IN THE INLET.
The ice mass occupies a typical glacial trough, shaped by an ice current flowing southeast- ward, or from the observer. Photographed June 10, 1899.
cent changes. Of the Carroll, Rendu, Geikie, and Wood we had only distant views.
Mutr Glacter.— The Muir Glacier is not only the larg- est of the group but the most accessible. It has been
FIG. 9. MUIR GLACIER.
Photographed June 9, 1899, from point on mountain spur at the east, a little lower than point Z£, fig. 1o.
MUIR GLACIER 21
visited by many ship-loads of tourists; it has received the chief attention of students of physical geography; and much is known of its recent history. Muir’s notes and sketches record the approximate position of its sea cliff in 1880, and photographic and instrumental determinations of its outline were made by Wright in 1886, and by Reid
LEGEND POSITION OF ICE FRONT
»~0288KKs FROM DESCRIPTION BY JOHN MUIR, IBSO —-~—:—- FROM PHOTOGRAPHS BYG.F.WRIGHT, 1886 —w-mwe FROM SURVEY BY H.F.REID, JULY 26,1890 *+e+¢0% FROM PHOTOGRAPH SY H F.REID,SEPT.7,1890 —*—+— FROM SURVEY BY'H.F.REID. JULY 19,1892
FROM PHOTOGRAPH BY M.F.REI0,AUG.19,1692 ———— FROM SURVEY BY HENRY GANNETT,JUNE 12899
reg
1880 Peet. lial
SCALE © 1000 2000-3080 ~=h000 = 8000 FEE?
FIG. 10. MAP OF NORTHERN PART OF MUIR INLET.
Showing position of front of Muir Glacier at various dates. Reid’s survey stations are
indicated each by a letter, dot and circle, with figures showing height in feet above mean tide. A and B were the extremities of his base line.
in 1890 and 1892. During our visit the outline was mapped by Gannett, who tied his work to monuments left
22 ALASKA GLACIERS
by Reid. The accompanying map (fig. 10) is copied from Reid, with the addition of Gannett’s line showing the con- dition on June 10-12, 1899."
From 1880 to 1886 the cliff retreated about 4,000 feet; from 1886 to 1890, 3,300 feet. Between 1890 and 1892 there was an advance of 700 feet; between 1892 and 1899 a retreat of about 1,900 feet, nearly the whole of the change occurring after 1894. The net retreat in nineteen years was 8,500 feet, or 1.6 miles.
Although several of these surveys were quite accurate, I have stated their results in round numbers, because ereater refinement would tend to mislead. The forward flow of the glacier probably varies little from day to day, but the breaking away of the cliff is quite irregular and the outline of the front continually changes. Besides this change in local detail there is a general change of more permanent character, to be described presently; and it is probable that an important seasonal oscillation interferes with the direct comparison of observations made at differ- ent times of year. The average annual retreat of the ice cliff for the four years preceding 1890 was 800 feet, and for the following two years the average advance was 350 feet; but Reid noted in the summer of 1890 a retreat of 500 feet in 43 days (July 26-September 7), equivalent to an annual rate of 4,000 feet. Again in 1892 he made two observations 31 days apart (July 1g-August 109), and these show retreat at the rate of about 3,500 feet per annum; but the whole retreat in the seven following years
1 Reid’s map is pl. xcva in 16th Ann. Rept., U. S. Geol. Surv., part 1, 1892. Gannett’s work was limited to the changed ice front and the resulting extension of the shore line. Field notes and photographs show that there were associated changes in the drainage of the gravel plains, but as these data are not sufficient for the correct delineation of the streams in 1899 I have left them as Reid repre- sented them. Some time before 1894 the northern branch of the western creek found a shorter course to the inlet, reaching tide about three-fourths of a mile nearer the glacier; and some time between 1894 and 1899 a similar change oc- curred on the east side of the inlet.
MUIR GLACIER 23
was only 1,900 feet. It is therefore probable that the summer rate of retreat is much more rapid than the winter.
While these considerations tend to qualify the figures deduced from uncorrected observations, they do not affect their general tenor. The application of a correction for seasonal oscillation would diminish by a few hun- dred feet the estimate for the total retreat from 1886 to 1890, and increase by a similar amount the estimate for the total retreat from 1892 to 1899, but would leave un- changed the general result that the retreat in nineteen years has been more than a mile and a half, and that the general retreat suffered at least one interruption, a small advance occurring between 1890 and 1892.
The general change of contour mentioned above is of peculiar interest because it was predicted by Reid. The middle of the glacier ends in deep water, a maximum sounding of 720 feet having been recorded, but at each side of the rock trough the ice rests on a bank of gravel rising above the water level. Observing that the surfaces of these gravel banks descend northward beneath the glacier, Reid inferred that with the progress of recession lanes of sea water would soon be admitted between the ice and the gravel; and having determined that the mar- ginal parts of the glacier advance very slowly as compared to the medial, he inferred that their cliffs would be carried back with relative rapidity by the attack of the warm sea water. As the map shows, these expectations have been fully realized.
In bringing the record of the glacier down to the sum- mer of 1899 the preceding paragraphs practically close a division of its modern history, for a new epoch was intro- duced only three months after our visit. On the 12th of September the southern coast of Alaska was shaken by a severe earthquake, and other shocks followed at intervals. These greatly modified the condition of its tidal glaciers,
24 ALASKA GLACIERS
and the Muir, at least, has not yet, after the lapse of three years, resumed its normal habit. Just what changes were made we do not know, because ordinary sources of infor- mation have been cut off and no student of glaciers has yet made an investigation.
On July 29, 1900, O. H. Tittmann, Commissioner for the United States on the International Boundary, visited Glacier Bay on the tourist steamer ‘Queen.’ In the lower part of the bay the main channel was so obstructed by floating ice that the commander of the vessel sought for an easier passage west of Willoughby Island, and finally desisted from the attempt to approach the glacier when opposite the mouth of Muir Inlet. Looking ahead it ap- peared to Tittmann that the whole of Muir Inlet was occu- pied by an ice pack, the ice being probably grounded and stationary. Instead of being able to steam as usual to the very front of the glacier, the vessel was turned back at a point about ten miles distant. In the summer of Igor tourist steamers were stopped by the pack at distances from the glacier ranging from five or six to eight or ten miles. In December of the same year a special trip was made by the ‘City of Topeka,’ for the purpose of forecasting the accessibility of the glacier for the excursion season of 1902. The way was then found comparatively open, and the steamer approached within about a mile of the gla- cier; but in the following summer the nearest approach was to a point five or six miles distant.
These facts seem to show that the earthquake shock, or shocks, not only set free a great quantity of ice, including bergs of unusual size, but left the glacier in such condi- tion that bergs were more easily detached in subsequent years. The determination of the nature of that condition will be of much interest to students of the physics of glaciers. Joint systems in rock have been plausibly as- cribed to the passage of earthquake waves, and it is easy
MUIR GLACIER 25
to understand that the comparatively weak and equally brittle material of glaciers may be still more susceptible to rupture by sudden strain. As the tension cracks inci- dental to the flow of glaciers are quickly welded, except near the surface, it would appear probable that earthquake cracks in the terrestrial parts of a glacier have no perma- nent effect of importance, but the case may be materially different in the parts encroaching on the sea.
As heretofore known, the frontal wasting of Muir Glacier has been chiefly by melting below the water-line, and the ordinary bergs, produced by the shearing off of the overhanging upper portion, have been of moderate size, readily floating away. ‘The greater bergs which stranded in the inlet after the earthquake may have been produced by cracks which divided the glacier from top to bottom.
Reid Inlet.— Glacier Bay parts at its head into three branches (fig. 7). The westermost division, Reid Inlet, receives the Grand Pacific Glacier from the northwest, the Johns Hopkins from the west, and the Reid from the south, the three fronts circling in compact order about the western or northwestern end of the inlet. In 1899 (as also in 1892) this was the region of most active berg formation, and on the day of our visit, June 12, the float- ing ice was packed so closely as to stop our progress — with a rowboat — and we succeeded in reaching only the Reid Glacier. With the use of a plane-table, a map was made of the lower end of Reid Glacier, and imperfect topographic sketches of the ends of the Johns Hopkins and Grand Pacific; and the data thus obtained were after- wards combined with the representations of the same dis- trict by Reid’ and the Canadian Boundary Commission to produce the sketch map in fig. 11?
1 Sixteenth Ann. Rept. U. S. Geol. Survey, part 1, pl. Lxxxv1, 1896.
*There is some confusion as to names of glaciers about the upper part of Glacier Bay. Muir, the explorer of the region, gave manuscript names, some
26 ALASKA GLACIERS
In the original exploration of Reid Inlet in 1879, Muir found it headed by a single great glacier whose ice cliff spanned the fiord from wall to wall, being interrupted only by a single boss of rock, half island, half nunatak. This glacier he named the Grand Pacific. When Reid in 1892 found and mapped two great glaciers, besides a third of moderate size, Muir wondered and was perplexed, for it did not seem possible that he could have overlooked two tidal glaciers; and it was not until he revisited the inlet in 1899 that the mystery was solved. During the thirteen years which had intervened between exploration and sur- of which received newspaper publication. Reid, who made the first survey (1892), adopted Muir’s names and added others, his nomenclature being first fully published in 1896 ( Sixteenth Ann. Rept. U. S. Geol. Survey; text and map). The Canadian International Boundary Commission, surveying the same region in 1894, prepared maps witha different nomenclature. These maps, be- ing primarily for the use of commissioners in connection with the pending boundary question, have not been officially published, but they have been unoffi-
cially distributed and their data compiled in various maps. The following are the discrepancies :
Feeid’s name. Can. B. Com. name.
Glacier reaching Reid Inlet from
the north. Grand Pacific. Johns Hopkins. Glacier reaching Reid Inlet from
the west. Johns Hopkins. No name. Glacier reaching Rendu Inlet. Rendu. Charpentier. Glacier reaching Hugh Miller
Inlet from the south. Charpentier. No name. Glacier reaching Queen Inlet. Carroll. Woods. Glacier reaching Geikie Inlet
from the south. Wood. No name.
It would appear that the cartographer of the Commission had moved three names — Johns Hopkins, Charpentier, Wood(s)—from the glaciers to which they were attached by Reid, and given them to other glaciers, displacing the names given to these others by Reid. No new names are added, and the dis- placed names do not appear elsewhere.
Reid’s nomenclature is followed by the U. S. Coast Survey in chart 3095, Glacier Bay (1899). The Canadian Commission is followed by the U. S. Coast Survey in chart 8001, Northwestern coast of North America (edition of 1898), and in chart 3091, Territory of Alaska, southeast section (1898). Otto J. Klotz, an officer of the Canadian Survey, in the Geographical Journal (vol. x1v, 1899), uses Reid’s name, Grand Pacific, in his text (p. 529), but in the titles to two figures (pp. 527, 529) applies the Commission name Johns Hopkins to the Grand Pacific Glacier of Reid.
Reid’s names have recently been adopted by the U. S. Board on Geographic Names. See National Geographic Magazine, vol. x11, page 87, 1902.
REID INLET 247
vey the main trunk of the Grand Pacific had disappeared, leaving three of its branches as independent tidal glaciers. The name has been retained for the northwestern branch. In 1894 the district was resurveyed by the Canadian Boundary Commis- __ ieee sion, and another ae es mY wea TOR Gri i” iio eves
record was made of Y and
<< ogre SS aor Whe: Grand sPas WJ, a
cific in 1892 and 1894, as in 1879, presented two fronts to the waters
of the inlet, the 7 = V7 wp eed ipa ghee A 8
island, but in. the FIG. II, MAP OF HEAD OF REID INLET. later years a much Showing positions of ice front in different years. Land areas are ruled. larger part of the island was laid bare. In 1899—as nearly as my distant views enabled me to determine — the western and greater arm of the inlet had eaten back into the glacier so as to reach some distance beyond the head of the island and approach the mainland at the northeast, thus isolating a body of ice lying between the island and the mainland. The arrangement of moraines delineated by the Boundary Commission showed that in 1894 this body had ceased to be replenished by the current of the Grand Pacific, so that its complete wasting was a mere question of time.’ It is possible that in 1899 it had become so far reduced as no longer to touch the island.
1These moraines are beautifully shown in one of the Commission’s photo- graphs: A. J. Brabazon, No. 45, vol. 14, p. 13.
28 ALASKA GLACIERS
The front of Johns Hopkins Glacier has suffered less change since Reid mapped it, but there has been some retreat. A comparison of photographs made in 1892 and 1899 shows that more rock is exposed at the south; and a remnant of ice I could see clinging to the mountain side at the north showed that the front had within a very few years held a position several hundred yards more advanced than in 1899. Its determined changes were so small that no attempt has been made to express them in the accom- panying diagram.
The remaining glacier of the three was indicated in a general way on Reid’s map of 1892, but its lower end was represented by a dotted line, implying doubt as to its pre- cise position, and no name was attached. It was more con- fidently delineated by the Boundary Commission in 1894. As my map and photographs give such determination of the position of its ice cliff that future changes can be meas- ured, it seemed proper to supply Reid’s omission in re- spect to name, and the Harriman Expedition adopted the name Reid. I am glad to be able to illustrate somewhat fully a feature bear- ing a name so de- serving of honor in Alaska glaciology.
As already men-
tioned,the Reid Gla-
x cier was a branch of FIG. 12. REID GLACIER; en See VIEW the Grand Pacific in FROM THE NORTH IN 1894. 187 9, but not many
From a photograph by A. J. Brabazon. years could have
elapsed before the recession of the latter made it indepen- dent, and it is probable that its end then projected some- what beyond the general line of the south wall of the
REID GLACIER 29
inlet. One of Reid’s photographs shows that in 1892 it had retired within the general line of the mountain front. The Boundary Commission’s map places it outside the position of Reid’s dotted line; and in 1899 it was a half mile within the limiting capes. A comparison of the Commission’s photographs* with my own indicates a re- cession of about 1,500 feet in five years, accompanied by an important modification of the character of the front. The removed portion was part of an ice cascade, and as there was little change in the thick- ness of the glacier, the terminal cliff in 1894 was much lower than in 1899.
I found three masses of dead ice, testifying to. the former greater ex- tent of the glacier. One of these masses 3 rested on a small ne. 13. REID GLACIER ; DISTANT VIEW FROM promontory just east THE NORTHEAST IN 1894. of the glacier front. A knob of marble is connected with the main mountain by a comparatively low saddle, and on this saddle lay a body of ice apparently several scores of feet in depth but almost wholly concealed by stones and gravel. This was outside the line of flow of Reid Glacier, and could only be a remnant of the mass of the Grand Pacific when that glacier occupied the full width of the inlet. It dated back to a time when the conditions were as observed by Muir in 1879, and its gradual melting had probably been in
From a photograph by A. J. Brabazon.
1Especially A. J. Brabazon’s No. 38, vol. 14, p. 11.
ALASKA GLACIERS
30
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(aie at Se bal ‘ a “A
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31
REID GLACIER
*(6z a8ed) Ar0jstyq [eIOe]S [edo] 9Y} Jo d3v}s dT] IVS We 0} ULSUO[Aaq JuBUMIAI ddt JUeUSEIs SIDAOD } J°] 24} 3B puno13s910; dy} Jo yueqg “MOUS ST, “Surjsem ATMO[S SI PUB DAOTH 0} PasEdd SEY YOTYAA Ja19e]3 94} JO JUeUMDI B ST IWS Oy} 12 HHS Sor 9714 94} Suturofpe sseur yep y ‘eismvo 24} Aq 74Snvo d19M VOOM UT jas [[eJ S}I SABA BUTI 94} pue s10Jeq Sno] Jou yr on} Mo1y poyied pey S1isqoor uy ‘br ‘3g 0} MarIA uOIUedmoD
*66g1 ‘z1 aNOf ‘IsVHHLUYON ZHL WOud ‘UaIOVIO aIau ‘SI ‘ora
| |) AN
32 ALASKA GLACIERS
progress for nearly twenty years. The other masses clung to the walls of the trough occupied by Reid Glacier, and were still continuous with the ice of the glacier, although they had ceased to move. ‘They were simply portions of the retreating glacier so well supported by the land that they had not fallen into the sea when the deeper parts of the ice stream were melted. They were partly covered by gravel and other rock débris, but still showed faces of white ice near their junction with the glacier. That on the west side extended about 1,200 feet beyond the general ice front, and the eastern mass was nearly or quite as long. From these remnants it is inferred that there was a some- what gradual shrinkage of the glacier after the record of 1894, and that it did not immediately assume the propor- tions observed in 1899.
The width of the Reid at its débouchure is seven-eighths of a mile, and the general height of its ice cliff about 100 feet. The frequent falling of ice masses during our visit gave the impression that it was discharging bergs rapidly, but the little bay before it carried less floating ice than the open inlet beyond.
The data compiled in the map of the inlet (fig. 11) are of unequal precision. The line representing the ice front in 1879 depends largely on the recollection of Muir, but his recollection is supported by notes and a landscape sketch made at the time. The fronts of Grand Pacific Glacier in 1892 and 1894 are believed to be close approxi- mations, but the front in 1899 has much less authority and may involve considerable error.
The total retreat along the axis of Johns Hopkins Glacier in the twenty years preceding 1899 was about three and a half miles, and the retreat of the Grand Pacific along the line of its western distributary was three and a half to four miles in the same period. Reid Glacier retreated a half mile after its separation, the period being some-
BERGS $3
thing less than twenty years. In 1879 the Grand Pacific had a total water front of over three miles; in 1892 and 1894 the separated glaciers presented a total front of more than six miles, the exposure to the sea being progressively increased up to that time. Afterward the length of front underwent little change, and should recession continue it will diminish. Unless the enlargement of the ice front was compensated by shoaling of the water, the sea had exceptional advantage for twenty years in its attack upon the ice, and this advantage may have been connected with the phenomenal rate of recession.
Bergs.—'The upper part of Reid Inlet in 1899 not only contained more floating ice than any other portion of Glacier Bay, but its bergs were of greater size than any others we saw. The one pictured in fig. 16 was ascer-
= i
7 “x as ee wr Mira Tt u fr aw a7 mi
Wm" itty, FIG. 16. ROCK-LADEN BERG IN REID INLET.
Poo af
™ by ul
oe cre
-. ee We ear nae Ng et age
Scale is given by a boat. The nearer face of the berg, black with embedded detritus, is probably part of the base of the parent glacier. Photographed June, 1899. tained to rise 76 feet above the water, and one of my companions who landed upon it and walked from end to end, estimated its length by pacing at 750 feet. Having my eye gaged by these measurements, I was able to form an approximate judgment of the size of other large bergs seen; and I estimated the largest, which was approxi- mately tabular and square in form, to measure 1,000 feet on each side and to rise 1oo feet from the water. The thickness was probably not less than 500 feet. These
34 ALASKA GLACIERS
dimensions raised questions as to the mode of calving. Reid, from studies of the Muir, inferred that waste along the ice front was chiefly from melting by sea water; and this melting, in combination with the forward flow of the ice, produced an overhang, resulting in the breaking away of the upper portion of the glacier by its own weight. Such observations as I was able to make at various ice cliffs were in full accord with his view, and the great bergs of Reid Inlet may perhaps have been formed in that way; but their size led me to wonder whether another process might not be involved. Many of the immense bergs of the Antarctic Ocean are tabular in form, and it is believed that they have the full thickness of the parent glaciers, which were protruded into the sea until actually floating upon its surface before the separation took place. In order that the Grand Pacific or the Johns Hop- kins should produce bergs of this type, it would be necessary that the depth of the fiord in front of the ice cliff | should be not less than seven-eighths the thick- ness of the glacier. Hugh Miller Inlet: — Hugh Miller Inlet oc- “no cupies an irregular re- WM rar pio™ Gps ‘Ma cess among the hills and FIG. 14. MAP OF HUGH MILLER INLET. mountains on the south- Showing positions of the ice front in different westside of Glacier Bay. years. Land areas are ruled. Rocky islan ds o f mo der- ate elevation half block its entrance and interrupt its sur- face. Charpentier Glacier reaches it from the south, ter- minating in a low ice cliff about seven-eighths of a mile
HUGH MILLER INLET 35
broad. The Hugh Miller, descending from the moun- tains at the southwest, spreads into a broad field north- west of it, and has a double discharge, one part coming eastward to the inlet, and the other going northward toward Glacier Bay. ‘The face toward the inlet is about three anda half miles long. The southern third overlooks the water in a low cliff, and the remainder presents a sloping surface black with accumulated rock débris. Though the land-locked inlet gives the floating ice scant opportunity to escape to the open bay,-very little was ac- cumulated at the time of our visit, June 11, and all the bergs were small. |
FIG. 18. TILL LEFT BY HUGH MILLER GLACIER BETWEEN 1880 AND 1890.
Photographed in 1899. The till is thin, but contains remnants of ice, and was englacial in part. The single bush visible, almost the only vegetation on the new ground, is a willow.
The dates of exploration and survey are the same as for Reid Inlet and the general history of change is strictly parallel. Muir observed but a single glacier, to which he gave the name Hugh Miller. Reid found two, and added the name Charpentier. With the aid of Reid’s map I was able to indicate somewhat definitely the extent of the sub- sequent recession, and Muir, in revisiting the locality with
36 ALASKA GLACIERS
me, was able tosay that the change previous to Reid’s survey was greater in amount than the more recent modification.
But after the lapse of twenty years Muir found it im- possible to recall the precise position of the ice front in 1879, and a subsequent study of his notes and sketches left the matter still in doubt. On the accompanying map (fig. 17) I have drawn two tentative lines, one crossing the inlet near its mouth, the other running northward from the peninsula which margins the Charpentier Glacier. The more conservative of these implies that the face of Hugh Miller Glacier retreated about one and a half miles between 1879 and 1892.
In 1892 Charpentier Glacier had two fronts, separated by its contact with a broad rock island or peninsula. One front, facing northward, was tidal; the other, facing north- eastward, was non-tidal, but ended close by the water.
wren : paul ia . ee rt ' i eee
‘Oia i} | Hh
Its surface was dark from the accumulation of rock débris, and its motion had probably ceased. Seven years later the tide-water front had retreated about one-third of a mile, thereby nearly severing its connection with the inert mass at the northeast (D, fig. 19), and the waste of the latter
ill
weal hi
FIG. 19. CHARPENTIER GLACIER IN JUNE, 1899.
t
HUGH MILLER GLACIER 37
had progressed so far as to render its surface almost black from the accumulation of residuary moraine stuff. These relations are indicated in figure 17. The condition in 1894 was intermediate between those of 1892 and 1899. A comparison of Reid’s photographs and mine shows also that the Charpentier had lost in thickness as well as area, the lowering near its front being estimated at about fifty feet.
As mapped and described by Reid, Hugh Miller Glacier rested at one point against an island, and only the portion south of the island yielded bergs. The northern division of the front descended to tide-water, but was covered at its margin by débris and had no cliff. In 1899 the front had retreated so as to open a narrow channel west of the island and expose the top of another island on which a tongue of the ice rested. South of this point the ice cliff had retreated westward to an average distance of 1,000 feet, the maximum being nearly 2,000 feet. It still yielded bergs, but sparingly, and was probably approach- ing a non-tidal condition. A large nunatak at the south, which was mapped and photographed by Reid, was more fully exposed than before, and a small one had appeared between it and the ice cliff. Near the northern end of the cliff the distortion of dirt bands and an uprising of the surface of the ice suggested that another rocky islet would soon be exposed. The retreat of the northern portion of the glacier face had laid bare a group of rocks projecting slightly above the water, and a larger rock knoll was gradually emerging. At one point it projected as a nun- atak about 150 feet above water-level, and farther on was revealed at the water’s edge. The average width of the space here abandoned by the ice is about 1,500 feet. (See pl. mt.) The condition in 1894, as indicated by photographs, was intermediate, but nearer to the condition in 1899 than to that in 1892.
38 ALASKA GLACIERS
At the northern margin of the Hugh Miller ice field, where it discharges toward Glacier Bay, there is some- what similar evidence of retreat. Muir’s sketch shows that this front reached tide-water in 1879, but was inter- rupted near its eastern margin by a small island. This detail serves to fix its approximate position as represented in fig. 17. Reid states that at the time of his survey it was non-tidal, but his map places the ice margin at the water’s edge. Photographs made in 1894 indicate a bare tract 1,500 or 2,000 feet broad between the ice front and the strand, and at the time of my visit the distance was 2,600 feet, the surface being chiefly occupied by ground moraine. The ice front in 1899 had a gradual slope, was covered by drift near its margin, and was traversed by a large medial moraine. Close to its front it received a tributary, cascading down a narrow valley from the west. The total retreat of the ice front at this point was prob- ably a little less than one mile in twenty years.
Getkie Inlet.— Exploring Geikie Inlet in 1879, Muir found it headed by a tidal glacier, to which he gave the name Geikie. His notes estimate its width as several miles, but do not serve to fix the position of its front. In 1892 Reid found that its front had receded so far as to convert its two branches into distinct glaciers. Retaining the name Geikie for the more northerly, he called the other Wood Glacier. The Geikie was tidal; the Wood barely touched the water at two points, but yielded no bergs; and the nearer corners of the glaciers were con- nected by a short body of motionless ice. Photographs made by the Canadian Boundary Commission in 18947 show that in the two years elapsed since Reid’s survey both glaciers had shrunk, the Wood receding several hundred feet and the Geikie about half a mile. The
1A. J. Brabazon, Nos. 32, 38, 39 and 40, contained in volume 14 of the official album, pp. 9, 32 and 33.
LA PEROUSE GLACIER 39
Geikie was still tidal. The two were still connected by stagnant ice, a long, narrow strip, partly protected from melting by moraine stuff. In 1899 we failed to reach the head of the inlet, so that my only contribution to its his- tory consists in assembling the observations of others.
LA PEROUSE GLACIER
Fairweather Range, which bounds Glacier Bay on the southwest, presents its other face to the open ocean. Its seaward face is bold and lofty, and the greater part of it is above the snow-line. While rugged in detail it is little complicated by foothill ranges, and from the ship’s deck we could trace a number of its long glaciers from end to end. Between its base and the sea there is usually a narrow foreland, but this disappears toward the east and broadens toward the west. At several points it gathers the alpine glaciers into massive piedmont sheets, and several of these approach or actually touch the sea. The La Perouse, at whose edge we made a landing, is of this type, being fed by alpine glaciers from the slopes of the range about Mounts Crillon, D’Agelet and La Perouse.
FIG. 20. LA PEROUSE GLACIER, 1899.
Showing the alpine glaciers that feed the plateau mass below; and the relation of the timbered ridge at the left.
Its extent in the direction of the coast is about three miles, the central portion ending in a lofty white cliff. The eastern third is darkened by a covering of moraine and appears to be separated from the water by a strand.
40 ALASKA GLACIERS
The western part is partly concealed by a timbered ridge running parallel to the coast (fig. 20). This ridge, which is probably a huge moraine of Pleistocene age, extends westward far beyond the end of the glacier. Our landing (June 18) was at the western end of the ice cliff, coincid- ing with the eastern limit of the timbered ridge.
The ice cliff facing the ocean at this point has the gen- eral appearance of the front of Muir Glacier, but its sub- merged profile is different. Instead of deep water it overlooks a shoal, from which boulders project here and there and on which we saw small bergs stranded. Very little floating ice was visible, and no large bergs. The cliff is evidently sapped at base by the wash of the waves, and the process which perpetuates it is closely similar to the process which main- tains rock cliffs along other portions of the coast.
The glacier, which farther west presses against the timbered ridge, flows past its end to the sea, and thus the extremity of the ridge occupies a reentrant angle in the margin of the glacier. FIG. 21. ere MAP OF MARGIN OF Close to the angle a stream
LA PEROUSE GLACIER. of water, escaping from the ssanicemea crams mast tie vin of glacier, has crossed the trees. Forest is indicated by stars, sandbeach ridge, eroding a deep gash, by dots. Approximate scale; 1 inch=2,000 feet. s
in whose walls the structure of the ridge is revealed. The walls are not clothed by vegetation, but are somewhat cumbered by the trunks of forest trees fresh-fallen from the crests on either side. The stream has been very active within the last decade or two, and it seems probable that all its work of erosion was
1If our visit was at high tide, this shoal may have been bare at low tide.
s
LA PEROUSE GLACIER 4!
performed within that period. The section it exposes (fig. 22) includes horizontal beds of blue clay, flanked on the seaward side by highly inclined beds of similar clay alternating with layers of sand. Both these are truncated above, and overlain un- conformably by a series of
horizo ntally FIG. 22. SECTION OF TIMBERED RIDGE NEAR
bedded gray- LA PEROUSE GLACIER.
4 Ss A, laminated clay. 2B, bedded clay and sand. C, bedded gravel, els, in which with angular boulders and trunks of trees. D, bouldery till, with
are incorpo- tree trunks. G, glacier.
rated large angular boulders and trunks of trees. This gravel is succeeded on the landward side by — and prob-
FIG. 23. BARREN ZONE AT MARGIN OF LA PEROUSE GLACIER (LOOKING SOUTH). The glacier is at the right. Between it and the forest is a tract occupied by fresh drift,
with sticks and logs. Photographed in June, 1899.
ably passes into—a bouldery till, which also contains trunks of trees. The clays and sands evidently represent an epoch when the coast was more deeply submerged than
42 ALASKA GLACIERS
now, but our meager facts include nothing to indicate either the date of their deposition or the date and manner of their deformation. The overlying gravel and till are clearly of glacial origin, and the gravel was laid down at or near sea- level. As itis now about 150 feet above the sea, it is evident that there has been a change here in the relation of land and ocean. The buried tree trunks tell of an advance of the glacier over a tract that had existed as dry land.
FIG. 24. PUSH-MORAINE NEAR LA PEROUSE GLACIER.
The glacier is out of sight at the left (compare fig. 23). The moraine, here 1o feet high, is crowded against forest trees, and includes crushed trees. Photographed in June, 1899.
The remnant of timber standing east of the stream val- ley was separated from the glacier at the time of our visit, by a belt of barren ground from 100 to 200 yards wide (fig. 23). This ground was occupied by bouldery till containing bruised and macerated branches and trunk fragments, and the margin of the timber showed unmistakable evidence of recent attack by the ice (fig. 24). The till had been
LA PEROUSE GLACIER 43
pushed up into the forest, forming a heap several yards in height, and stones and earth were mingled with trunks of trees and other vegetal débris. It was evident that the forest had recently extended somewhat down the slope toward the present position of the ice, and that atemporary enlargement of the ice field had crowded it back. This had occurred so recently that a younger growth of trees Y,
wS \ ss> *,*
OEE NY, st fey? Wi VW pind Wye’ &! : Verb i . ac } £ yah ee f A :
ee ee
FIG. 25. LA PEROUSE GLACIER—CONTACT WITH FOREST IN 1895.
had not yet started on the morainic ridge. Some of the overthrown trunks still retained their bark, though it had fallen away from most. The wood of the trunks was still sound, but some branches an inch and more in diam- eter had become brittle, and leaves and smaller twigs had fallen off. With the local woodman’s knowledge of the rate of decay inan Alaska forest it would be possible to estimate closely the date of the advance. To my inex- pert judgment it appeared probable that it occurred within the last decade of the century.
44 ALASKA GLACIERS
Since writing the last paragraph I have received from the U. S. Fish Commission a photograph made from the steamer ‘Albatross’ in September, 1895, and have repro- duced it in figure 25. This shows that the ice at that time was in actual contact with the forest.
In the standing timber, which comprises both spruce and hemlock, and also among the overturned trees, are trunks four feet in diameter, and during the whole life of these trees—a matter of centuries—this particular spot has been undisturbed by the ice. It is thus shown that glaciation has here attained within a few years a maximum not previously reached for centuries.
The locality of our visit records at least two glacial maxima. As the older till contains tree trunks, it marks an advance of the ice after an epoch of inferior develop- ment. The mature forest standing on this till records another long epoch of lessened glaciation, and the recent advance asecond maximum. It is possible that the epoch between the two maxima was of only a few centuries, but evidence to be mentioned in another connection indicates that it was much longer.
On our return voyage in July we passed this part of the coast at a distance of several miles, and I was able to note that the eastern margin of the piedmont division of La Perouse Glacier lay parallel to a forest margin, with an intervening belt of different color, presumably morainic, about 200 yards wide. Similar belts were also seen about the flanks of the next piedmont mass toward the east. These facts indicate that the recent advance recorded at one point on the front of La Perouse Glacier was an ad- vance of the whole glacier, and render it probable that the change was not confined to a single glacier.
The evidence from the crushing of the forest does not tell us whether during the long period before the last ad- vance the ice had approximately its present extent or ex-
YAKUTAT BAY 45
perienced an important minimum, but the latter history is rendered probable by comparison with facts recently de- veloped about other glaciers of the same mountain face. Lituya Bay, fourteen miles northwest of La Perouse Glacier, was explored in 1786 by La Perouse, who de- scribed and mapped the principal glaciers descending to it. Klotz has made a comparison of La Perouse’s account with the condition found by himself in 1894 (fig. 74), and shown that there has been a marked advance of the ice in both arms of the bay, the western glacier encroach- ing three miles on the water of the bay and the eastern two and one-half miles." The foot of Brady Glacier, twenty-five miles east of the La Perouse, was visited by Vancouver in 1794, and from a discussion of his descrip- tion Klotz concludes that the ice front was then at least five miles less advanced than in 1894. Muir in 1880 found the margin of the Brady against a mature forest whose territory it was invading. As the La Perouse lies between glaciers of the same range which have experi- enced a great advance, and as it has recently crowded against a forest, the probability is that its history resembles that of its neighbors and includes a great forward move- ment during the last century.
YAKUTAT BAY
In the neighborhood of Yakutat Bay a foreland fifteen to twenty-five miles broad separates the mountains from the open ocean. The bay lies partly in the foreland and partly among the mountains. The outer part, to which the name Yakutat is more specifically applied, is nearly twenty miles broad, but narrows toward the mountains. The inner part penetrates the mountain district for ten miles in a north-northeast direction, with an average width
1Notes on Glaciers of southeastern Alaska and adjoining territory. Geog. Jour., vol. xIv, pp. 523-534, 1899.
46 ALASKA GLACIERS
of three miles, and then turns to the right at a sharp angle, and, assuming the character of a narrow fiord, runs back thirty miles toward the south-southeast (fig. 26). It then passes from the moun- tains to the foreland, and ends in an oval expansion three miles wide. The shorter and broader reach within the mountains is called Dis- enchantment Bay; the long, narrow arm, Russell Fiord. Russell Fiord has two east-
FIG. 26. MAP OF YAKUTAT BAY AND ITS DEPENDENCIES. Based on map of the Canadian Boundary Comniission, with local ward branch-
details by I. C. Russell and Henry Gannett. es. The north- ern is at the present time about eight miles long, ending at Nunatak Glacier, and it is convenient to call it Nunatak Fiord. The southern, about one mile in length, leads toward Hidden Glacier.
The foreland southeast of the bay is in general low, but includes hills and ridges of morainic aspect. So far as known, it is wholly constituted of till and gravel, brought by glaciers and associated streams of water when the ice fields of the region were more extensive. Northwest of the bay the foreland is occupied (or constituted) chiefly by a great piedmont glacier, the Malaspina, the ice being
YAKUTAT BAY 47
separated from the water of the bay by a belt of detrital lowland. The mountain system is lofty, and among its summits are great tracts of névé. From these a series of alpine glaciers stream down to feed the Malaspina, and others reach or approach the land-locked arms of Yakutat Bay. Turner Glacier, entering Disenchantment Bay from the northwest, flares at the end after the manner of the Davidson, but has not yet surrounded itself by a moraine barrier, and ends in a berg-producing cliff. The Hubbard, coming in two principal streams from the north and with minor afHluents from the east, reaches the sea at the junc- tion of Disenchantment Bay with Russell Fiord and
- occupies the coast for more than five miles. Nunatak
Glacier flows northwestward to the end of Nunatak Fiord, where it maintains a discharging cliff nearly a mile broad. Hidden Glacier, with branches from the east and south, follows a trough parallel to Nunatak Fiord, but fails to reach tide-water, being separated from it by a gravel-plain two miles long. |
Two islands should be mentioned here, not as importan geographic features but as landmarks to which the follow- ing pages make occasional reference (see fig. 27 and pl. vit). Haenke Island, a rounded rock knoll several hun- dred feet high, lies near the east shore of Disenchantment Bay. Osier Island, lower but containing also a nucleus of rock, stands at the entrance to Russell Fiord.
The inner arms of the bay were explored by Russell in 1890 and 1891, and he prepared a sketch map showing the general relations of fiords and glaciers. The shores were afterward surveyed by the Canadian Boundary Com- mission (1895), and during our visit Gannett made local maps of the upper part of Disenchantment Bay and the ends of Nunatak and Hidden glaciers.
The prevailing rocks are friable sandstones and partially altered shales, and these are weathered and eroded much
48 ALASKA GLACIERS
more readily than the rocks about Glacier Bay. For this reason the finer details of ice sculpture are preserved only on surfaces from which the glaciers have somewhat re- cently retreated. It is probably because of the rapid weathering that vegetation occupies ice-freed surfaces rather quickly, but this remark applies only to herba- ceous plants and to willows and alders having the habit of bushes. The spruces, whose dense forests cover the detrital foreland east of the bay and climb the seaward slope of the adjacent mountain, have accomplished little toward the invasion of the most freshly glaciated faces of the same mountain which are turned toward Yakutat Bay and Russell Fiord.
So far as known by direct observation, the recent glacial history is one of waning and retreat. From a careful compilation of early records, made by Russell, it appears that Malaspina in 1792 and Vancouver in 1794, attempting to penetrate Disenchantment Bay in boats, found a glacier front at Haenke Island. This was essentially the face of Hubbard Glacier, to which the Turner was then trib- utary. Completely filling the head of Disenchantment Bay, it acted as a dam separating Russell Fiord from Yakutat Bay, and the fiord was then occupied by a lake. The discharge of the lake must have been southward over the gravel lowland, and during its existence the wash of its waves produced beaches which are still to be seen as terraces about the southern part of the fiord. Russell estimates their height above tide-water at 150 feet.
From 1792 to 1899 the face of Hubbard Glacier re- treated about five miles, but there is no reason to suppose that its position in the days of Malaspina represented a maximum. Haenke Island, which was not wholly cov- ered by the ice at the time of Malaspina’s visit, neverthe- less preserves glacial striation over the whole of its crest, and in places even polish; and this could hardly be the
YAKUTAT BAY 49
case if it had been exposed to the weather for more than one or two centuries. Moreover, there is no change in the vegetation at this point. The alder thickets which begin at the head of Disenchantment Bay, characterize the slopes of the mainland not only to Haenke Island but for miles beyond, and the first spruces noted were not less than five miles to the south of the island. But while the ice seems to have recorded neither a maximum nor a pro- longed lingering at the point where it was earliest observed, our present data suggest no other line of critical impor- tance. We can only say that for a period considerably greater than a century the general character of ice change has been diminution.
Since the last paragraph was written, the U. S. Coast and Geodetic Survey has published a new chart of Yaku- tat Bay, giving soundings from the ocean to Point La- touche, six miles below Haenke Island. These sound- ings give no indication of a moraine in the vicinity of Point Latouche. Not far from that point there is a depth of 1,000 feet, and thence southward the channel is shown for five miles. Here, at a distance of twelve miles from Haenke Island, is a submerged bar with a depth of about 300 feet, and this is probably the last-formed important moraine in the bay. There appears to be another oppo- site Knight Island, seventeen miles from Haenke Island, the intervening hollow having an extreme depth of about 600 feet (see fig. 27).
This is the greatest distance to which the channel of the Hubbard, or Disenchantment Bay Glacier can be clearly distinguished. Its course is not central to the bay but nearer the eastern shore, the Disenchantment Bay stream apparently having been crowded over by the ex- pansion of the Malaspina Glacier, which then included the Lucia. Farther to the south and southwest the soundings reveal a series of troughs and ridges whose trend and
50 ALASKA GLACIERS
curvature suggest that they are connected with earlier positions of the margin of Malaspina Glacier, and these corrugations end against a great shoal which spans the mouth of the bay from cape to cape. This shoal is slightly convex toward the ocean, and its submergence ranges from 50 to 80 feet. It is believed to mark a former extension of the seaward face of Malaspina Glacier.
DEPTHS IN FEET
[je — 150-300 == 300 - 450
450 - 600
600-750
750 - 800
900-1050
are —
FIG. 27. MAP OF YAKUTAT BAY, SHOWING CONFIGURATION OF BOTTOM. Adapted from U. S. Coast Survey. Places where no soundings were made are indicated by ??.
All or nearly all of these ridges are probably connected with the Pleistocene history of the region, but the moraine
RUSSELL FIORD 51
midway between Point Latouche and Knight Island may correspond to a comparatively recent maximum of the Disenchantment Bay Glacier—that from which it was retreating when observed by La Perouse. <A more intel- ligent judgment can be formed when the system of sound- ings shall have been carried through Disenchantment Bay. Turning attention to Russell Fiord, we find pertinent phenomena somewhat more abundant, and it seems pos- sible that their careful study may yield important chapters of the local history. The lower parts of the fiord walls are finely sculptured, showing by magnificent flutings that there has been much longitudinal scouring. At various points, but especially south of Hidden Glacier, there are marginal banks of gravel similar to those about Muir Glacier, characterized by horizontal bedding but showing by their surficial forms that they have been overridden and molded bya glacier. Nearly all parts of the walls of Russell Fiord carry vegetation, of which the alder is a conspicuous element, but the growth is relatively sparse toward the north and dense and luxuriant toward the south. The gravels about the basin at the extreme south- ern end bear a luxuriant and mature forest of spruce. Looking back to the time when Russell Fiord was filled by a glacier, it seems evident that the ice stood for a con- siderable period with a front just outside the mountains. The expansion of the fiord in the edge of the foreland corresponds, I conceive, to the flaring end of David- son Glacier, and the surrounding plain of gravel is the equivalent of the moraine barrier which the Davidson has built in Lynn Canal. This condition is assumed to date back several centuries, for it is not probable that the forest could occupy the whole surface of the gravels until the ice had retreated. The banks of gravel within the fiord record lingerings of the ice front and subsequent re- advances, but whether these oscillations preceded or fol-
52 ALASKA GLACIERS
lowed the epoch when the entire fiord was filled with ice is a matter of doubt.
Coming to this region while the features of Glacier Bay were fresh in mind, I searched gravel and till, wherever opportunity offered, for vestiges of earlier forests which might have been overridden by the glaciers, but the search was unsuccessful; and so far as my evidence goes, the condition of expanded glaciers observed by Malaspina and Vancouver may not have been preceded in this locality and in recent geologic times by a condition of relatively contracted glaciers such as now obtains. Rus- sell found a buried forest under the foreland gravels at the south end of Russell Fiord,’ but the demonstrated oscillation need not have been of great extent.
flidden Glacier.— The valley in which the distal part of Hidden Glacier lies is a characteristic glacial trough with rather uniform cross-section. Its course curves from northwest to a little south of west, and it joins Russell Fiord at right angles. In 1899 for a distance of a mile and a half it was occupied by tide-water with a width of three-quarters of a mile; then came a tract of gravelly alluvium, nearly two miles long and a little narrower than the inlet. The glacier itself had a width of a mile. The ice front sloped gradually down to the alluvial plain, and although the profile was slightly arched, its greatest de- clivity (measured on a photograph) was only ten degrees. In the lower mile the surface was remarkably smooth and there were no important crevasses. There were lateral moraines, and near the southern of these a single strong medial, but the general face was exceptionally free from drift. Close to the front margin the ice was somewhat discolored, but so nearly white as to suggest that the lower layers, usually dark with englacial drift, were not visible. That they really lay at some distance below the
1Thirteenth Ann. Rept. U. S. Geol. Survey, Part 11, p. 89, 1893.
ee ee eee
BioddiseaoioslO nobbi * Mioid Moeaus rort
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~.892 off bas tion! | i orli 3% ,2noitiaoq ocd} est
TD D NS GLACIER
ra Wie y> F ai ’
HAE ;VorIl
SCALE
ys Res Ae bats | MILES
owed the 4 oh aw: = + fatter of foul . e Arr the rhs re aio werw fresh mn ind, a searched gravel and t il, W neortunity otferedy for vestiges of earlier : i rests might have been overridden by me glacies iy be En e § RS unsuccessful ; and so far as my avi ence : dition of expanded glaciers 0 ia r ed a 4 Vancowver may not. have been. preceded it cality and in recent geologic times bya condition | vclarively contracted glaciers such: as NOW obtains, ) fowsd « buried forest under the foreland gravel _ EXPLANATION OF PLATE Ive dem 101 i ‘tla Sy re Ppt haye been of great. extent. Mt dabei tet he a o_o allt hel te Hiden Glacier, Bord. the sea at spel thendk wat ing from Russell F > Ww] ele. map. For ‘hese
Bay, oh ee For
cord the ce Site 1 delta.
Offiée drawing ty Giles Gilbert
Tree Shee a hough the atl was.slightly arched, its phe clivity (measured on a photograph) was only ten deg the lower mile the surface was remarkably smooth a ere were no important crevasses. There were late -aines, and near the southern of these a single stro out the general feee was exceptionally free from to the front mangin the ice was somewhat seohored, but so measly wiite a8 to suggest that the wer ja vers, analy dark + th — al drift, were. ne ie Phat they wally legeat somme distance below. the | |
nae tus. Reet. TC. & Heclewaertep, Fart Wi) p 89, 1893.
i a
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AMIOGe KAGE WO TAI
53
‘IIPeIS aq} Aq popots puv uapprz ~I9A0 U9Eq SBY YOM ued o}svM Japjo uv Jo JMVUMMIAI dy} ‘JaAvIS poyt}erjs A[OpNI SI 39] 94} IV ‘sIapR[s VAsely AURI YIM pozeloosse sured ajseM 4[INq “Mv91}s ‘Ua1IBq 34} JO WOTSIRSNITI [VoIdA} & ST YS ye puL[Mo] ay, ‘aur au ‘19;9U]F JO z1ed J[qQISTA JO UIPIM “pnoyd Aq paTesou0d aie adUe SIP 9IIaI}.Xa 3Y} pus SUTEJUNOME JO SPTMIMING }saAy}IOU 9Y} WioIy Uses aay SI yT ‘(92 “Sy pue Ar ‘{d 99s) ysva aq} moy ‘Avg jeynyAeA ‘piorg ppessny sayovoidde rapes ayy
‘6691 ‘oz ANAL ‘URIOVID NAACIH ‘ez ‘Ola 8
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HIDDEN GLACIER
=
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54 ALASKA GLACIERS
visible glacier snout and were extended along the floor of the valley beneath the gravel plain, seemed to be shown by other phenomena. First, the water of ablation, though flowing out from the surface of the glacier near each side, did not visibly escape from the ice in the central part, but oozed up through the contiguous gravels, gathering in a number of streams, which attained their full size about a quarter of a mile from the ice front. Second, the gravel plain in the vicinity of the ice front was dotted by numer- ous pits, the larger of which contained lakelets. The sides of these pits were steep and exhibited the stratifi- cation of the gravel in section, the pits having evidently been formed after the gravel was deposited; and there can be no doubt that they originated from the melting of buried ice and the consequent sapping of the gravel bed. The ice whose melting was thus demonstrated may have been part of a continuous sheet or may have constituted a series of isolated masses, but in either case each local mass must have reached its position as part of the glacier. The history seems to be, that the waning glacier was so reduced by the wasting of its surface near its end that the débris of its moraines, worked over by glacial streams, overspread the ice and buried a wide belt. At the time of my visit this was gradually and irregularly melting, under the influence of underground waters, and by its melting was sapping the gravel plain.
This process is of interest to students of Pleistocene glaciology, because it is evident that with a slight change of conditions it might lead to the formation of familiar features of the ‘ modified drift.’ If the locality lay some- what higher above tide, and if the glacier were so situ- ated that, with the progress of its melting, the water of ablation would be drawn off in some other direction, the gravel plain would be left intact except for such changes as resulted from the melting of the ice beneath it. Where
MH. A. BE. ¥OLiti
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Ive «
EXPLANATION OF. PLATE, V-
KETTLE-HOLES NEAR HIDDEN GLACIER
Kettle-holes are ascribed to the melting out of ice masses that had been buried by the rapid accumulation of gravel or sand. In the cases pictured the burying material was gravel washed from Hidden Glacier, and the ice masses were originally part of the glacier.
The Upper Figure shows a fresh-formed example, the steep walls exhibiting the gravel deposit in section. It shows also the gentle terminal slope of the glacier, the smooth sculpture of its valley wall,. and the mouth of a hanging valley. See pages 55 and 118. |
The Lower Figure shows a less advanced stage of the same phe- nomenon. After settling had commenced, the spot received a deposit of mud, and this mud was cracked as the settling proceeded. |
Photographed by G. K. Gilbert, June, 1899. Negatives Nos. 371 and 372, United States Geological Survey.
HM, A, Es VOL Il
PLATE
he T PLE-HOLE
INCIPIENT KETTLE-HOLE
HELIOTYPE CO., BOSTON.
KETTLE-HOLES 55
that ice was approximately or wholly continuous, its melt- ing, being temporarily concentrated here and there by underground currents, would let the gravels down un- equally and leave them, in the end, in a system of irregu- lar heaps identical with kames. Where the surviving ice comprised only isolated or scattered masses, the waste of — these would let down the gravels immediately above them, producing steep-sided, crater-like kettle-holes, and creat- ing the familiar phenomenon of a pitted plain.
The upper figure in plate v reproduces a photograph of one of these fresh-formed kettle-holes, lying near the visi- ble portion of the glacier. Its dimensions were 220 feet by 70 feet, with a depth, to the water surface, of eight feet. Its wall was divided at one point by an outlet channel leading to a neighboring glacial creek. An incipient kettle-hole seen about a mile below the glacier is repre- sented in the lower figure. This had been overflowed by water from one of the glacial creeks, so as to receive a layer of mud, but the water had retired before it was wholly silted up. It is evident that the meandering of streams over the gravel plain would eventually obliterate all of the kettle-holes, so that their preservation must de- pend upon some permanent diversion of the streams.
The stream escaping from the north edge of the ice front was traced backward to an ice cave among the hil- locks constituting the lateral moraine. It was evident from an examination of the local topography of the ice surface that the débris had great influence on the rate and method of wasting, and reciprocally, that the wasting modified the distribution of the débris. Where the dé- bris was more than a few inches thick it retarded melting, producing an ice hill; but from these hills the stones slid down to the neighboring hollows, producing accumula- tions which in turn retarded melting and caused a new distribution of hills. Some of the hills were elongate,
56 ALASKA GLACIERS
and may have marked the position of original moraine belts, and one of these happened to be cut across by a glacial stream, so as to be exhibited in section. In the photograph reproduced in plate vi the ice, which is here rather dark from suffused dirt, is seen to constitute the mass of the morainic ridge, being preserved from melt- ing by a relatively thin layer of fine drift.
Russell, who saw and named the glacier in 1891, did not visit it, and merely records that it was non-tidal. His map makes no claim to precision and can not be used in a com- parative way to determine the history of change. Gan- nett’s map, pl. rv, and the various photographs here repro- duced, make a record which will be available for future comparison, but inference as to past changes can only be based on circumstantial evidence. That the recent history of the glacier has been one of recession can hardly be doubted. Not only do the kettle-holes testify to the stag- nation and burial of what was formerly its snout, but I found remnant ice masses above the gravel plain on both sides of the valley. These were protected from rapid waste by gravels that were originally parts of lateral moraines, but as water was constantly flowing from them their survival could not be indefinitely prolonged, and their origin can not have been remote. They were not seen more than a half mile from the ice front, but they lay considerably above the neighboring gravel plain, the . extreme height at the north being estimated at 300 feet, and at the south somewhat greater. When the back of the glacier reached to these heights its front probably extended a mile farther down the valley.
The walls of the valley are not clothed with vegetation,. but a scattering growth of annual plants and a few dwarf willows have found foot-hold. The gravel plain through which the glacial streams meander, though seemingly affording conditions of soil and moisture congenial to
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MEMIOTYPE ¢: BOSTOr
EXPLANATION OF PLATE VI
1 Upper Ficure.— PROFILE oF HipDEN GLACIER
Shows the relation of the glacier snout.in, June, 1899, to. topo- graphic details of the south wall of the valley. . In the foreground are _ bedded gravels that have been overridden, eroded, and grooved by the enlarged glacier, and are now being trenched by running water.
The amphitheater high in the mountain shows familiar forms of - aqueous sculpture but is not continued downward ina gorge of com- § - mensurate size. The gorge probably once existed, but the containing spurs were removed by ice erosion at a time when the glacier was much larger than now.
See page 52, and compare figure 28.
Photographed by G. K. Gilbert, June 20, 1899. Negative No. 368, United States Geological Survey.
LoweER FiGureE.— SECTION OF MORAINE
Shows the structure of one of the ridges of the northern lateral mo- raine of Hidden Glacier. See page 56.
Photographed by G. K. Gilbert. Negative no. 370, United States Geological Survey.
» A;
~ast te . . +2 oe ela < a
Ee. YOu. il
_~
PROFILE OF HIDDEN GLACIER
SECTION OF MORAINE
HELIOTYPE CO., BOSTON.
HIDDEN GLACIER 57
arctic willows, was absolutely barren (fig. 29), and a sim- ilar barrenness was observed on other fresh-formed streams of glacial waste. The perpetual stream of cold air flowing down from the ice above may be in part responsible for
FIG. 29. WASTE PLAIN OF HIDDEN GLACIER IN JUNE, 1899.
The rock fragments washed from the glacier are built into a delta plain, to which addition is being made. In the foreground is an alluvial fan encroaching on the plain; in the dis- tance, Russell Fiord.
this, but I conceive the chief cause to be rapidity of dep- osition. The high grade of the plain, in comparison with the breadth of its channels and the moderate coarseness of its gravel, gave the impression that it was being built up with great rapidity. —
As in Russell Fiord and its other appendages, the valley walls exhibit the flowing contours of glacial sculpture in magnificent development. There are many places where the smooth curves of the mountain side, carved out in harmony with the flow-lines of the ice, suggest the sweep- ing contours of a gigantic ship, rather than the billowy backs of a flock of sheep described by the word mou- tonnée. A system of flutings can often be traced in sim- ple curvature for a half mile, and no one familiar with the
58 ALASKA GLACIERS
topography resulting from stream erosion can fail to be impressed with the profound modification here wrought by the ice. (See fig. 102.)
As the extent of the glaciers has varied, masses of gravel and other drift have been lodged here and there on the valley walls and afterward overridden, and where the subsequent action has not sufficed for their removal they have been carved into forms harmonious and continuous with the contiguous rock forms. Here and there, where the rills of the valley wall have trenched these deposits so as to expose them in section, one may see horizontal bedding in a mass of gravel whose external surface ex- hibits only the smooth curves of flowing ice. One of the larger of these gravel masses lay close to Hidden Glacier, against the lower slope of the north wall of the valley (pl. v). Upon its sculptured back were scattered boul- ders left by the ice which had recently overridden it, and among them were a few great blocks of white granite, brought from some distant source. Descending toward the glacier, the surface of this gravel mass ran under one of the remnants of unmelted ice to which reference has already been made.
Nunatak Glacier.— Nunatak Fiord, like the fiord of Hidden Glacier, has been boldly sculptured by ice. Its lofty south wall descends steeply to the water and is com- paratively simple in contour. The north wall is in gen- . eral lower, is flanked by heavy masses of gravel and other drift, and is interrupted by two branching troughs leading over saddles of moderate height to the northern part of Russell Fiord. These troughs seem to have been largely shaped by the ice, which flowed through them to the northwest. One is now bare, but the other contains an ice mass with the habit of the dying glaciers of Glacier Bay. ‘The mass receives a small tributary glacier near its summit, but the end seen from Nunatak Fiord in 1899
+ m
ETO” BODY EV.
OE i ee = ae | 2 ~ . ‘ “ hy
EXPLANATION OF PLATE VII
Mar or NunATAK GLACIER
Nunatak Glacier reaches the sea at the head of Nunatak Fiord, an arm joining Russell Fiord at right angles. See map of Yakutat Bay, figure 26. ,
This map is based on a plane-table sketch by Henry Gannett, made from stations on the north shore of the fiord, June 20, 1899. Special: pains were taken to make record of the ice cliff terminating the north arm of the Nunatak Glacier. Its south arm, and the minor glaciers, were added from photographic data and eye observations, without the aid of instruments.
Drawn by Gilbert Thompson.
See pages 58-63.
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59
NUNATAK GLACIER
“AdT[VA Sursaey & JO YyNOUL 9y} Aq poysoSSns st YI JO JUS} xO 3T]} ‘WOITSOID DT 0} SINOJWOD TIOOMIS S}ISOAO PIOTY AVJVUNN JO[[VM IYI, ‘PIOWT []ossny jo [TV Jsam oy} 18 ‘pno[d Aq payesou0d A[jied ‘sure}uNOM jue SIP BL *‘plOLY [[assny 0} pO AeyeunN wMop soo] pue ‘(+ -Sy) IF So}VUIWI9} YIYA YIP 94} IvsU ‘IaIOV[H AejyeunN jo pueg uleiowm vB UOSpUE}s I9AIISqO dT,
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60 ALASKA GLACIERS
was probably stationary and wasting. It was heavily coated with drift, which lay in irregular hummocks. The opposite end was not identified, but may be one of the branches of the stagnant portion of Hubbard Glacier, to be described on another page.
Close to the end of Nunatak Glacier were two lateral glaciers which may recently have been its tributaries.
LOO N\\|
FIG. 31. TIDAL FRONT OF NUNATAK GLACIER.
Beyond it, a hanging valley, with a small glacier. The heights are hidden by cloud. Photographed from the southwest, June 21, 1899.
That at the north (fig. 31) occupied a trough trending nearly east and west and intersecting the Nunatak at an acute angle. It terminated several hundred feet above the Nunatak, its lower part being buried under a heavy | moraine. That at the south (fig. 32) probably occupied - a yet higher valley nearly at right angles to the Nunatak trough, but clouds cut off the view of its upper portion. It was seen only as a series of ice cascades, pouring from ledge to ledge for a thousand feet down the steep wall of the trough.
The main division of Nunatak Glacier was tidal, dis- charging bergs freely from a cliff nearly a mile long and about 200 feet high. At the south the cliff ended against
a bold rock shore, but at the north it terminated among gravels, and a nar- row remnant of ice, half buried, extended several hundred yards west of the main mass. Near and east of the position of the glacier front is a high rock ter- race against the south wall of the valley, and this culminates at the east in a bold knob, thoroughly smoothed and rounded by recent glaciation. Inthe hollow separating
mass of ice of uncertain relations (fig. 33).
NUNATAK GLACIER 61
SSAA SEF Sheers - 4 . EE
—_ es
wn Sakis * Ves : Ses ce a
S eeteall
FIG. 32. CASCADING GLACIER IN NUNATAK FIORD.
The visible portion of the glacier has no valley, but descends wallof valley of Nunatak Glacier. Photographed June 21, 1899.
this knob from the south wall lay a It was seen
FIG. 33. SOUTH TONGUE OF NUNATAK GLACIER IN 1899.
- only from the west,and was | supposed to bea tongue or distributary arm of Nun- atak Glacier. The fact that it lay several hundred feet higher than
62 ALASKA GLACIERS
the tidal arni has raised doubts as to the correctness of the first impression, and I now suspect that it was only the remnant of a former arm of the glacier, stranded as a motionless and slowly wasting summit mass. On the map of the Canadian Boundary Commission (1895) it is repre- sented as a distributary of the glacier.
At the time of Russell’s visit in 1891 the glacier flowed _on both sides of the high rock knob (fig. 34) and was re- united beyond it, so as to convert the knob into a nunatak; and it was this conspicuous nuna- tak near the end of the glacier which suggested its name. The retreat of the ice front in the = Se ee Se intervening eight years FIG. 34. TIDAL FRONT OF NUNATAK GLACIER. Call not have amounted
Photographed from the north, by D.G. Inverarity, to less than a mile and June 21, 1899. The camera stood on the glacier.
may have been twice as great. It was nearly all accomplished in the first half of the period, for the photographs made by the Boundary Commission in 1895' show a complete separation of the two arms and a close approximation to the condition of 1899. ‘The tidal arm was perhaps a third of a mile more advanced in 1895, but the non-tidal was not appreciably longer. It is possible, however, that the latter extended for some distance in a stagnant condition beneath a mantle of drift, for at the time of our visit there appeared to be remnants of ice ina moraine belt stretching for a mile be- yond its extremity.
The accompanying map (pl. vir) is based on the sur- vey by Gannett in 1899, supplemented by photographs. It is accurate as to the ice front and contiguous land, but
1Nos. 20 and 45, on pages 7 and 17 of vol. 17 of the official album.
HUBBARD GLACIER 63
only approximate in its reproduction of the other portions of Nunatak Glacier and the neighboring ice bodies.
Hubbard Glacter.— The Hubbard Glacier, discovered by Russell in 1890 and named by him in honor of Gardiner G. Hubbard, president of the National Geographic So- ciety, is the most important ice body of Yakutat Bay. Its width where it reached the bay was, in 1899, five and one-half miles, its whole frontage, counting the sinuosities of outline, being about six miles. Of this frontage the southeastern third was motionless, and fringed for the most part by a belt of morainic débris. The remainder, pushing itself forward into the head of Disenchantment Bay, maintained an imposing ice cliff nearly 300 feet high. The active portion of the glacier had two main branches, the larger coming from the east or northeast, the smaller coming from the north, and the two uniting only three miles back from the water. Looking up the valley, we could see a number of minor tributaries descending from the bordering heights, but the principal sources were con- cealed from view, and the low grade of the main trunks suggested that their beginnings were far away. ‘The sur- faces of both branches were rugged, being divided by a labyrinth of crevasses into a wilderness of pinnacles. Morainic bands marked out the lines of flow, and a broad belt of ice near each margin of the active portion was black with included débris. The more southerly of these belts was continued to the water front, causing a black ice cliff nearly a mile in extent (fig. 35). The correspond- ing belt at the north appeared to have become nearly sta- tionary, as though resting on a rock shoal, and the flow- lines of the northern arm were curved about it.
The southeastern third of the glacier was moraine covered, not only at the water edge but for nearly or quite two miles inland. The material was coarse and angular, and was divided into zones or belts distinguished at a
ALASKA GLACIERS
64
‘XI puBIIIA saqetd sIVdMIOD “Ivy IOTIN J, |OUvySIp 94} UL ‘S}ITM PUB Uva] puodaq nq ‘d}SBA YOOI POPNOUT Y}IAA OV] SF }t Aqiean “Avg Jam yWEYOUASIG BAOgB 392J COL SI9MO} JoPOBIS 9} JO HHP 2t ouL
66g1 ‘1 ENaf ‘uaIOVIO auvasnH ‘Sf ‘old
7 y —a be - * =
HUBBARD GLACIER 65
distance by their contrasted colors— black, yellow, purple, green, blue-black, and orange or rusty. These bands had not the ordinary arrangement of parallel medial moraines, but tended rather to contour the slope, and the search for their origin and meaning would make an interesting and profitable study. Some of them occupied ridges and others hollows, suggesting inequality in their ability to retard the melting of the ice beneath, but the whole surface was rugged in detail, exhibiting a continuous series of hum- mocks and kettles.
The map given in plate vi11 was made by Gannett from a series of stations at the south, the northern shore of Dis- enchantment Bay being inaccessible by reason of floating ice; and some of the details, especially of the moraines, were added by the aid of a series of photographs made from a high station on the mainland near Osier Island. Russell in 1891 (September 5) stationed his camera on Osier Island; and a comparison of his photographs with mine (June 22, 1899) shows that there was little change in the general character and condition of the ice cliff. My views place it one or two hundred feet farther back than his, and this difference would probably be increased if the proper correction for season could be applied (p. 22), but in any case the estimate of the whole retreat would not ex- ceed a few hundred feet, and would be very small as com- pared to the retreat of Nunatak Glacier in the same period.
A photograph taken from Haenke Island in 1899 is also comparable with one from the same station by the Cana- dian Boundary Commission in 1895,' each showing the relation of the northern part of the ice front to the features of the contiguous mountain face; and in this case also the recorded change is small.
Another series of photographs were made by the U. S. Fish Commission in 1go1, chiefly from Osier and Haenke
1No. 13, on page § of vol. 17, official album.
66 ALASKA GLACIERS
Islands; these show a continuance of retreat. At a point where a prominent moraine makes the comparison some- what definite, the ice cliff appears to have then stood 700 to 1,000 feet farther back than in 1899. The cliff was also shortened at each end by the enlargement of the marginal belts of stagnant ice.
Turner Glacier.— Turner Glacier comes into Disen- chantment Bay from the northwest, a few miles below the foot of Hubbard Glacier. As already stated, it was tributary to the Hubbard a century ago, and was ren- dered independent by the retreat of the latter. Immedi- ately after its isolation its front may have projected some- what farther into the bay than in later years, but it is not probable that the difference was great. A comparison of Russell’s photograph made from Haenke Island in 1891 with my own made eight years later from the same station (pl. x) shows no appreciable change in the position of the front.
The general width of the glacier within the mountain is about one mile, but it begins to flare before fully emerging, and at the water front was nearly two and one-half miles broad in 1899. For a width of about two miles an ice cliff was maintained by the falling of bergs, and the cliff was flanked on either side by a sloping tongue which, from our distant view, seemed black. Russell’s picture represents parts of these tongues as white, so that in these marginal. portions a progressive change is recorded. There was also a change in the flow-lines, as indicated by moraines near the southwestern margin. A strand of the ice which had previously swung far to the south had in 1899 ac- quired a more direct course to the bay, reaching the cliff 1,200 feet to the northward. This would seem to indicate that a body of ice near the south end of the water front had in the interval become stagnant and, acting as an ob- struction, had deflected the current.
WESTON
HELIOTYPA
EXPLANATION OF PLATE +X"
Uprer FicureE.—TuRNER GLACIER IN 1891
Photographed by I. C. Russell, September 5, 1891. | Negative No. 556, United States Geological Survey. 7
Lower Ficure.—TuRNER GLACIER IN 1899
Photographed by G. K. Gilbert, June 22, 1899. Negative No. 317, United States Geological Survey.
Each of these photographs was made from near the summit of Haenke Island, the stations being practically identical. The changes in the glacier from 1891 to 1899 are discussed on pages 66-67.
The position of the glacier, on the west side of Disenchantment Bay, is shown in plate vu and figure 26.
*“NOLSO8 ‘'O9D 3dALOIISH
6681 NI YSIOVIS YSNYNL
Bea
gi. ee on: Meare ge eis!
L68t NI YSIOVID YANYNL
xX -3lvd Wl “IOA °3 °V CH
TURNER GLACIER 67
Since writing the preceding paragraph I have been able to extend the comparison by examining photographs by the Canadian Boundary Commission and the U. S. Fish Commission. That by the Boundary Commission was taken from Haenke Island* in 1895, its record being midway between Russell’s and mine. It shows the con- dition of each feature as intermediate between the phases of 1891 and 1899. That by the Fish Commission was taken from Osier Island in 1901. It shows an extension of the frontal cliff, as compared with the condition in 1899, and probably indicates renewed movement in mar- ginal ice which had become stagnant.
There is an important morainic belt on each margin of the glacier, with outlying ribbons, and a single well-defined medial moraine reaches the water front near its middle.
The visible portion of the glacier within its mountain valley has a moderate grade, but at its débouchure into the main trough of Disenchantment Bay there is a steep descent, the surface falling 500 to 600 feet in a quarter of a mile. The grade then suddenly diminishes to almost nil, and the glacier terminates in a platform of nearly uni- form height, with a width ranging in different parts (1899) from 1,800 to 3,500 feet.
The ice cascade at the point of débouchure indicates a drop in the rock bed where the Turner trough joins the greater trough of Disenchantment Bay, and this feature is related to the phenomena of hanging valleys, to which special attention will be given in another chapter. The flatness of the terminal portion of the glacier is a peculiar feature, not so strikingly exhibited to us in any other in- stance. It is of course possible that the longitudinal pro- file of the glacier bed is here horizontal, and that the ice is everywhere supported by a floor of rock or drift; but it seems to me more probable that the flatness is due to
1 No. 12, on page 5 of vol. 17, official album.
,
68 ALASKA GLACIERS
flotation. If the glacier rested ona solid support there would be retardation from the friction on its bed, and this resistance would tend, under the laws of glacier motion, to produce a surface gradient.
If it be true that the ice is floated, then the sea water has access to its under surface, and the rate of melting is greater than would obtain if the front only were exposed. Should an increase take place in the supply of ice from the névé, and consequently in the size and speed of the ice stream, the end of the glacier would be thrust farther out on the water of the bay, but this extension would in- crease the surface exposed to melting, and the loss thus occasioned would soon check the enlargement. The op- posite result would follow a diminution in the supply of ice, and the equilibrium between supply and waste would thus be maintained without great modification of the form and extent of the ice front. There would of course be progressive modification from the silting up of the bay. Direct melting of the under surface of the glacier before the mass is broken up into bergs would tend to localize the deposit of drift, so that the accumulation under the ice would be quite rapid, and eventually the drift floor would rey: ; reach up to the ice
Fey a
es ois mS Ch and subglacial melt-
Wy Z yy = oe ee ee ing would be 4, Wy Tipe Tae. (a ee
ae Y ~- 7: = -4) Checked, ee oe a Ee Le If the glacier
floats, its thickness
FIG. 36. HYPOTHETIC LONGITUDINAL SECTIONOF can be estimated TURNER GLACIER.
from the measure- ment of the visible portion. In water of such density as Reid observed in Glacier Bay, the ice of glaciers floats with about seven-eighths of its mass submerged; and the thickness of the visible portion of the tabular mass in question would be one-eighth of the total thick-
OSIER ISLAND 69
ness. The central part of the Turner ice cliff in 1899 was 250 feet high, but as the surface of the glacier was greatly dissected by crevasses its average height above water was somewhat less and may be roughly estimated at 220 feet. This would give for the total thickness 1,760 feet, and for the submerged portion 1,540 feet. The theory that the glacier floats, thus implies that the bay has a depth close to the northwest shore of 1,600 feet, and the central depth should be considerably greater. The theory could there- fore be tested by sounding.
Oster Island.— The little island at the turn from Dis- enchantment Bay to Russell Fiord (see pl. vir) is a low knoll constituted of the altered shales of the Yakutat for- mation. A rocky reef extends northwest from it, and a gravel spit, bare at low tide, joins it to the mainland. It has three faces, characterized by cliffs telling of active erosion by waves. ‘The east face is turned toward Rus- sell Fiord and receives the waves generated by southerly and southeasterly winds in a straight stretch of deep water nineteen miles long and from one and a half to two miles broad. A high cliff testifies to their efficiency, and so does the gravel spit just mentioned, to which they have brought not only pebbles but large boulders. The north face, which has a rock cliff of equal or greater height, is turned toward the ice cliff of Hubbard Glacier, 6,000 feet distant. The wind waves that reach it from Russell Fiord have only two miles at most in which to develop. Wind waves from the head of Disenchantment Bay, four miles distant, might reach it, and on rare occasions they probably do, but that part of the bay, being overlooked by the most active part of Hubbard Glacier, is ordinarily full of floating ice, which prevents the generation of such waves. Instead of wind waves the chief attack is by ice-fall waves. From four miles ofice cliff the bergs are breaking, and the cannon- like boom recording the sundering of one of the greater
70 ALASKA GLACIERS
blocks came to our ears every five or ten minutes. As each block fell, it started a series of circling waves, many of which were so largeas to make breakers miles away, despite the damping effect of the floating ice. The breakers we observed on Osier Island were formidable enough to en- force much caution in landing, and the series from different ice falls followed one another so closely that there were few intervals of quiet.
The southwest side of the island is sheltered from all winds except westerly and, as it borders a cove which westerly winds would pack with ice, may never feel the force of wind waves. Ice-fall waves reach it from Turner Glacier after a journey of four miles, and by shorter, but deflected, courses from the Hubbard. Its shore cliffs are much lower than those of the other sides of the island.
In 1794, when Hubbard Glacier reached to Haenke Island, Osier Island must have been ice-covered and sub- ject to glaciation, and it was not bared until more than half the subsequent wasting had been accomplished. It is therefore probable that the existing shore cliffs, esti- mated from memory as 25 to 30 feet high, have been carved out within a few decades. During part of this time the ice-fall waves reaching the north shore were more effective than now because the ice cliff was nearer.
From these various features, and especially from the comparison of the north and east shores of the island, it appears that ice-fall waves have very notable ability to erode coasts, an ability fairly comparable with that of wind waves. ‘This fact is of value to the student of Pleis- tocene glacial lakes, as it enables him to understand the clear outlining of their coasts in cases where the indicated extent of the water surface is too small for the generation of important wind waves.
SO Riate Xi 5 ee
fi
a Ae, " > oe eh tang epee me IN ne eg nn
end al ewe ee ee
MAM OF COLUMBIA GLACIER = : ; . SOBUK ‘. ‘
——— es wae _ — Pei aed seh
ra a A! AS t
Mpc PaseiMe to Our ears ey: Teh bei, tt started a Bee “6 ; which were 50 kenge to eli x GH pine fect of the iat: i observed on Oeter Ishend were or id ) pera hegaee force much autvon am das ling, veal the waries froma aitenent ice falls followed oat esodifer a clowmy that: tere: were
few intervals of quiet, | The southwest side of the land is sheltered Sci all” _Winds except westerly and, as it borders a cove which — westerly winds would pack with ice, may never feel the rce of wiad waves, -Ice-dall, waves reach it from Tune
lacier alte APG OF ir? bi mr deLeotenl, eae
clits are ee lever olumbia Glacier reaches oe sea at t
or the el 6. ~Frinc ey Pek end dee 1 | 9, tl rns | | : fe ip:
Drawn by Gilbert Thompson. _ bead been uncannplicher 3 coat
Contour tele 250 feet. the hay a repagsentes | ab} ee |
At lowest tide tegen ys is mh 'o islands north of red alon
flats, and extensive Shoals’ are ba 3 ; glacier is described on. rt. Itis pictur
3 and XII, and in figure 37. 37. WAVES reaching the 4 re mare effective fs an now bécause the ice elit ce
5 cy. —
rrom these various features, and ehipeedaliy from the mparison ef the nerth and east shores of the island, it | appears that hee-fall waves have very ‘notable ability to ee erode coasts, an ability faitly comparable with that of @ wind waves. This fet is of value to the student of Plews focene glacial lakes, as # enables him to understand the a lear outlining of thelt eoasts in cases where the indicated 4 mt of the water surface is foo eemall for the generat a
MEPOTtant Witt waites,
H.A.E. Vou. Iil Puate XI
ce) | f Hal bY ; wa th k ' \ tims 1 in}: +2000 Be [dy \L et ase ~ fl : \
See:
4 = re 7
MAP OF COLUMBIA GLACIER SCALE o | 2 3 he 5 6 MILES
F { j i | {
a a eel
ee ee
Le EMT MEL em
Ne aS Ban . —— am ewe a ee ee ee PP RE TTR Le I LA te RTM 6 EC IT, SMT rN men - Ta -~ i n
Misc tb?
PRINCE WILLIAM SOUND 71
COLUMBIA GLACIER
Between Yakutat Bay and Prince William Sound we made no landing, and our course lay too far from shore for observations of value on the glaciers.
Prince William Sound is an extensive and intricate body of water, penetrating a mountain district. Its numer- ous islands and peninsulas are mountain peaks or ranges, and many of its inner arms and passages have the char- acter of glacial troughs or fiords. Among the mountains of the mainland at the east and west are many small gla- ciers, and a great mountain mass at the north supports extensive névés from which magnificent ice rivers flow to its northernarms. It was my good fortune to be landed at the mouth of one of these ice rivers and, in company with Palache, Coville, and Curtis, to spend several days in its study. Many photographs were made and some map- ping was done.
In June, 1794, this glacier was seen from the mouth of the associated bay by Whidby, one of Vancouver’s officers. Vancouver says: ‘To the eastward of this is another bay of rather larger dimensions, with an island in its northeast corner, . . . terminated by a solid body of com- pact elevated ice, similar to that which has been before described ... 3; as they passed the eastern bay they again heard the thunder-like noise, and found that it had been produced by the falling of the large pieces of ice that appeared to have been very recently separated from the mass extending in vast abundance across the passage . . . » insomuch that it was with great difficulty the boats could effect a passage.” ?
The bay and island appear on a map in Vancouver’s atlas (see fig. 42). The bay (without the island) is rep-
1A Voyage of Discovery to the Pacific Ocean and round the world, etc., Capt: George Vancouver, vol. v, London, pp. 316-317, 1801.
72 ALASKA GLACIERS
resented on a map prepared in connection with expedi- tions to Alaska under Glenn and Abercrombie, in 1898, and the same map also indicates the presence of the glacier, but neither bay nor glacier is delineated with sufficient accuracy to serve as arecord for future comparison. The name Columbia was given by the Harriman Expedition.
The general course of the glacier is southward, and its width in the lower ten miles is from three and a half to four miles. Its sources are distinct and were not seen, but beyond the tract covered by our map (pl. x1) it appeared to spread somewhat broadly, and the ice field affording its chief oe may send streams in other directions also.
Wm Cen ve a
FIG. 37. PANORAMA OF COLUMBIA Shows the western division of the front.
About nine miles from the sea it encounters an outlying mountain over 3,000 feet high, by which it is divided, the principal current passing to the west. The eastern arm descends steeply for three miles and terminates in a - land-locked valley against a plain of glacial gravel. A subdivision of the western arm enters the same valley. In 1899 it barely touched the eastern arm, so that the moun- tain was wholly surrounded by ice and could properly be called a nunatak. Beyond this point the main stream flowed to the ocean, but the surface grades descended also toward lateral valleys, and there was waste all about
1Maps and descriptions of Routes of Exploration in Alaska in 1898. U.S. Geological Survey, 1899. Map No. 8.
COLUMBIA GLACIER 73
the periphery. On the east side the ice rested against three low hills, beyond which were lakes supplied in part from its melting. In one place a lobe of ice touched one of the lakes. Ina hollow on the side of one of the hills a lakelet was imprisoned by the ice, one of its shores being constituted wholly by the glacier. On the west is an embayment among high mountains, into which the ice sent a tongue two miles long, but there was no lake and no visible outlet for the water, which must have found its way to the sea beneath the body of the glacier. This feature is specially remarkable from the fact that the sub- glacial water could not follow the course of the ice, but for
vay NORTHEAST a Z
>
v O <P aa y 6 235 fe 2S es, Ui Mi.. - ey
GLACIER, FROM THE SEA.
From photographs by W. H. Averell, June, 1899.
several miles must either move in the opposite direction or take some independent route.
Columbia Bay, to which the glacier flows, is from four to five miles broad and is locally divided by a group of islands. ‘The western arm, two and a half miles broad, is comparatively simple in outline and is probably deep. It received the principal discharge from the glacier, which spanned it from side to side with a cliff about 300 feet high. The eastern arm, irregular in outline and judged from the configuration of its shores to be comparatively shallow, was bordered by the glacier for a mile and a quarter, but the ice cliff was less lofty, and a compari- son of its outline with other portions of the glacier showed
74 ALASKA GLACIERS
that the water controlled the form of the ice front to only a moderate extent. The principal island of the group, to which we gave the name Heather, is nearly three miles long and has an irregular surface, rising at one point to a height of 500 feet. It consists chiefly of rock. Several lower islands lie north of it, and the ice front rested against one of these for a space of 3,000 feet. The number of islands varies with the state of the tide, and it is pos- sible that all are united at lowest tide.
Opposite the great nunatak were two medial moraines, one passing within a half mile of its base, the other lying about one mile from the opposite edge of the glacier. A central tract two miles broad was practically drift-free. Toward the end of the glacier this central tract broadened, the medials swinging toward the sides, until finally the white belt was three miles wide. As the medials diverged they also broadened, and they eventually merged with flanking moraines, so that near the end, especially on the east side, the areas of drift-covered ice were very wide. The marginal belt on the west, instead of continuing north- ward parallel to the medial with which it was associated, was seen to curve about into the western embayment, as indicated on the map, and a belt seen from a distance near the north edge of the embayment was supposed to be its continuation, a loop being made within the embayment. As the ice in the embayment descended toward the west, it is evident that the morainic loop could not at that time represent a line of continuous flow, for we can not suppose the ice to flow into the embayment on a descending course and then return on a parallel ascending course. It is therefore probable that the moraine was formed as a com- paratively direct line of drift, following the course of the main ice current at a time when no current entered the embayment. The inference that a change has oc- curred naturally leads to enquiry as to the precise nature
74
Tuet tre erat: b@beseratc «x yeah, v | which we nw the name Heather, ia: rly Mong ar - at irregular surface, rising atone sailed fo a "g height ry 506 feet, It consists chiefly of tock, ‘Several. lower \siamets Tie north of it, and the ice! front rested — against one of these for a space Of 3,400 feet, The number of islands varies with the state-of Peeiserats it is at sible that.all are united at lowest tide... Opposite the great nunatak were two medial maonatniiny |
one passing within @ half mile of lee baer, the other lying’ F about one mile from the o opposite edge of the glacier. A
centr a}
plate x1. cane r poy ae nannies a ' tive Nt + pho raph 8 py de by ES. bee aia ge Meee !
ne oth edgr anf Fee. cmbey meet was Borin © en its continuation, Mp being made within the embayment. As the ice in it embayment descended toward the west, ic is evident that the morainic loop could not at that time represent a line of continuous flow, for we can not suppose the ice to flow into the embayment on a descending coursé and then return on a- paralle! asecnding course, I[t-is— therefore probable that the nae tere formed ms. a come iratively direct née oof dei, # 13 Rn Tage the ¢Ourse of ie main ice Gurréhf at a —_ ik: mo current.entered i@ embayment. The. inferwses: that a change has-oce _ | wel naturally leads to ers aigaetD the precise ee an
: =—s- an 4 -
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oad 32 08719 .
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COLUMBIA GLACIER 75
of the antecedent condition of the glacier. On the one hand, the embayment may have been so full of ice that the surface gradient was outward; or, on the other, the glacier of the main valley may have had so low a surface that there was no tendency to overflow to the comparatively shallow side valley.
The first case implies snow accumulation in the embay- ment a few decades ago at a rate not since maintained, and would correspond to a general expansion of glaciers followed in later decades by contraction; but the rela- tions of the ice to the forest, to be described presently, show that such contraction has not taken place. The second case implies a general expansion of the glacier as the important element of its later history.
Another medial moraine of the great ice field north of the nunatak passed just east of the nunatak and continued down the eastern arm of the glacier to its end, where it contributed toward the building of a great alluvial delta which was gradually obliterating one of the lakes.
At the western margin of its principal tidal cliff the glacier rested on a bank of drift at the level of low tide, and this bank extended eastward as a shoal, on which bergs were stranded, for several hundred yards from the shore. A bank also extended eastward from the island against which the ice front rested, constituting at low water a stony cape half a mile long near the foot of the ice cliff. These banks testify to a lingering, or linger- ings, of the ice front near the position of its modern maxi- mum, but it is not easy to estimate the duration of the lingering. The western bank is built in deep water, but may have been constructed rapidly, as the contig- uous portion of the glacier is heavily charged with drift. The eastern bank margins a part of the glacier front carrying little débris, but occupies an arm of the bay which
76 ALASKA GLACIERS
was probably originally shoal. They may have been formed recently, or at some earlier epoch.
The drainage of the ice included several streams flowing eastward to the chain of lakes, and we noted two important streams from the western ice cliff. One of them issued from a cave at the water’s edge near the western limit of the cliff, the other from a sub- merged and invisible tunnel near the middle of the cliff. The last mentioned was probably the largest of all the draining streams. It rose to the surface at the base of the ice cliff and flowed southward over the salt water, forming a broad lane of milky fresh water with a visible cur- rent and at times nearly free from floating ice.
At most points the forest of spruce and hem- lock approached close to the ice, its relation being similar to that ob- served at La Perouse Glacier. At the western
FIG. 38. WESTERN EDGE OF margin of the main ice COLUMBIA GLACIER. f : Shows barren zone and forest. From a cliff, where the glacier
rock slope, there was a belt of bare rock, from 200 to 300 feet broad, between the ice and the forest (fig. 38). This belt was strewn with fragments, not only of rock but also of wood, and trees were freshly overthrown at the margin of the forest. At the time of its attack on the forest the ice must have been 100 feet deeper than in the summer of 1899, and it also extended farther southward, as shown by a push-mo- raine of rock at the water margin, 800 feet from the
COLUMBIA GLACIER "7
ice front (fig. 39). A second push-moraine, less massive than the first, lay within it, being 160 feet from it at the water margin and elsewhere nearer to it than to the ice. On the island between the two ice cliffs
there were FRE SSN ee A also two push- FRRSO¢, SAAS a moraines of MASc Se Se oe
FIG. - PUSH-MORAINE, WEST SHORE OF COLUMBIA BAY. recent date, 39 ;
the nearer being about 100 feet from the ice front, the farther from 300 to 500 feet. The latter was associated with overthrown forest trees, and included with its rocky
FIG. 40. FLUTED MORAINE AT EDGE OF COLUMBIA GLACIER. Photographed in June, 1899.
débris not only tree trunks and branches but folds of peaty soil. The tract between the nearer push-mo- raine and the ice was in places occupied by an old mo-
78 ALASKA GLACIERS
raine surface over which the ice had advanced, and this surface was elaborately fluted in the direction of ice motion, the corrugations having a vertical magnitude of several feet (fig. 40). In one instance it was seen that a large bowlder in the underlying drift had im- pressed its form on the ice, preserving in its lee a train of drift of the same cross-section, which constituted a ridge, and it is probable that the other flutings were of the same character. As these details in the con- figuration of the drift surface would be quickly ob- literated by frost and rain, their exposure must have been very recent. Probably the advance creating the push-moraine and the subsequent melting which laid bare the ice-molded drift had taken place within one or two years.
On the mainland at the east the same phenomena were observed, with the exception of the fluted drift surfaces. There was an inner push-moraine, chiefly or wholly of drift and running parallel to the ice margin. There was an outer push-moraine, less regular in its distance and associated with disturbance of the forest and the meadow peat (fig. 41).’ In the tract between the two many prostrate trunks were seen, showing that in places the front of the forest had been crowded back several hun- dred feet. Many of the trees that were overturned but not overridden, retained their bark, branches, and even minor twigs, but the leaves had fallen. On disturbed forest soil Coville found three young spruces which had grown since the catastrophe. In each case the age, as shown by rings of growth, was seven years. The date of the ice maximum was therefore not later than 1892 and may have been that year.
1The view in fig. 41 is toward the northeast — along the front of the push- moraine. A little of the steep face of the glacier is seen at the left. At right is a tract of undisturbed bog.
79
COLUMBIA GLACIER
‘90d ANV LSHUOA NO UAIOVIO VIAWN'IOD AM MOVLLV ONIMUVW ANIVUOW ‘IF ‘OTA
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Y bas A EY # TI a
80 ALASKA GLACIERS
The overturned forest trees associated with the push- moraines on the eastern and western shores of the bay and on the island, exhibited the same general appearance of recency, and there can be little doubt that they were dis- turbed at the same time. ‘They demonstrate a temporary increase in the size of the glacier, not of precisely the same amount at all points, but of the same order of mag- nitude. Previous to that expansion the glacier had been smaller during a period at least sufficient for the growth of the overturned trees. The evidence from forests and push-moraines does not show whether the ice during this epoch stood continuously near to the forest or was sub- ject to wide oscillations in extent; but the bending of the moraine belt on the back of the glacier into the western embayment (page 73) gives strong support to the view that the recent maximum was preceded by an important minimum.
No attempt was made to estimate the age of the trees by counting rings of growth, but the forest had the char- acteristics of maturity, and the time required for its pro- duction could hardly have been less than two or three centuries. ‘The mountain side just west of the glacier, rising steeply to a height of 2,000 feet, is clothed with a luxuriant growth from the push-moraine up to about 1,500 feet. Many of the trunks are three or four feet in diam- eter, and among them lie prostrate logs in a state of de- cay. Upon the islands, and on the lowland near the east margin of the glacier, the trees are somewhat smaller, but the many dead trunks standing among them indicate that they are mature, and their term of life may be as long as that of their western neighbors.
A further item of information as to variation, albeit somewhat indefinite, may be derived from Vancouver’s map. It is not sufficiently precise to afford identification of any topographic detail of the bay except Heather Island
us Nesey are mately
oo ae
14 4 oA AKIVEA
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ee ee me
A ee ec ee ect
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aed forest trees, uae stern and Bi:
nit ude P evious 0 ee at expane rn Dh. smaller during a period at least su ees OV wotecto trees, The ev
sa h-moraines does not show wh s poch s poe con a neat t et re Pn Wa am So
An index 5 the sound, showing. pos sitions of Columbia Plc ased_ chiefly” on United § States Coast Su:
no wae 3%
idence from Z eee a . : 3
Bs as ne Base des ~ eh eal NO. 3091. he i tt) rae by te
“Lowen Fioune.—Skeren or
"Surveyed by. Henry Gannett, | bert , Details al
cher, and an mong hese “fie pros strate S toek in a ste de
cay. Upon the islands, and on-the lowland near. gfe 3 argin of ¢ the glacier, the trees are somewhat smaller, 4
many dead trunks standing amon ¢ them indicate. hal a re mature, and their tert. of i ide may be as. long |
2a~ Ail LAL “their western ndighbe ese *
rther item of information ss © variation; all t jj finite, may Be derived from Vancouy
ERR eo uficien nth iy precise to ; ifford identification :
T8744}? . i 5 Te ry EE a en ok mos to popra hte detailef the bay except H eather. - "F 7 » - . oll
-HLA.E. Vou Ill : PuaTe XIll Z —r ca ra
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bad 147 7
PRINCE WILLIAM SOUND
GLACIER | ah ied? iy a
5) CRESCENT GLACIER
NORTH
SKETCH OF PORT WELLS
AHOCEN &CO. BALTIMORE
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Pee ee wee wr pear geet teneeers
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PR, eh 4 ¥
COLLEGE FIORD 81
(see fig. 42), but the narrowness of the strait represented
between the island and that portion of the coast said to 2
consist of ice, in- dicates the impres- sion of the explorers that the ice wall stood not very far beyond the island; and this view is supported by the Sa statement already
FIG. 42. OUTLINES OF COLUMBIA BAY. quoted that the
A, enlarged from Vancouver’s map (1794), whichdoes jsland was in the not distinguish the glacier from other parts of the land. ‘“ 9 B, reduced to same scale from plate x1, showing relations northeast corner
of sea, glacier, and land in 1899. O f the bay. I t seems reasonable to infer that the glacier was not much smaller in 1794 than in 1899; and that if the features of the em- bayment prove a recent and important minimum, that minimum occurred in the nineteenth century.
COLLEGE FIORD
While our boat party was occupied with Columbia Glacier the main division of the Expedition visited the northwestern arm of the sound, called Port Wells, where important contributions were made to geographic knowl- edge. College Fiord, the right branch of Port Wells, was explored more thoroughly than ever before, and the left branch, Harriman Fiord, was discovered as well as ex- plored. The fiords were mapped by Gannett, and their beautiful and imposing series of glaciers were photographed by half a dozen cameras. After the ship had picked up my party in Columbia Bay, it returned to Harriman Fiord for Gannett and Muir, and I was thus enabled to sail past several of the Port Wells glaciers, but the following de- scription is chiefly at second hand. Many of the best
82 ALASKA GLACIERS
photographs of the Port Wells glaciers are reproduced by photogravure to illustrate the narrative of the Expedition, and, to avoid needless repetition, I have selected for my own use only the views most important in connection with my text, but I shall refer freely to the plates of volume 1.
College Fiord is from two to three miles broad and about twenty miles long, trending north-northeast and south-southwest. Near the south end, where it joins the main body of Port Wells, there is a bay on the east side overlooked by two non-tidal glaciers. The larger of these was called Amherst by the Expedition, the name being given in honor of an American college. Somewhat north of the middle the fiord sends an arm to the northeast, and this arm receives a large tidal glacier, the Yale. At the head of the main fiord is the Harvard, also a large tidal glacier. Several branches of the Harvard were visible from the ship, and that next to the ice front on the north- west was named Radcliffe. A series of glaciers on the northwest side of the fiord resembled the Radcliffe in general character, and four of these received names— Smith, Bryn Mawr, Vassar, and Wellesley.
Amherst Glacier was passed by the ship at some dis- tance, and its features are known chiefly through the pho- tographs secured by Merriam (pl. x1v). It is fed by névés in full view from the fiord, and approaches the sea in a short, broad stream which at first descends steeply — and afterwards more gently. The habit of the lowland lying between the glacier and the ocean indicates that it is built of morainic material. Near the sea is a belt of timber, but this is separated from the ice by a barren tract similar to that about Davidson Glacier. A barren zone several hundred yards broad is seen to flank the glacier on the southwest, and a similar zone borders its companion, Crescent Glacier. These features doubtless indicate shrink- age in modern times, the change having been of moderate
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ei
-
EXPLANATION OF PLATE XIV
AMHERST AND CRESCENT GLACIERS
The Amherst Glacier is at the left, in the view, the Crescent at the right. These glaciers are on the east side of College Fiord, at its junction with the main body of Port Wells. Their position is shown in plate xin. See pages 82-83.
From a photograph made by C. Hart Merriam, June 26, 1899. Negative No. 124 of the United States Biological Survey.
UMEIOVIH LNSOSHUO UBIOVIDH LSUBHNy
Oa Bzostgs
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YALE GLACIER 83
amount, although greater than in the case of La Perouse and Columbia glaciers. The Crescent is comparatively narrow, and approaches the sea with a higher grade. A curve in its trough conceals its upper course.
The Yale drains a larger area and receives a number of tributaries. The front of the cliff is wide, but of moderate height, and a blackening, west of the middle, by englacial drift suggests that a rock knob may lie near the surface, ready to develop into a nunatak or island if the glacier shall diminish. The trough in which it lies is forested along the water edge on both sides for the greater part of the distance from the main
fiord to the = glacier, but SSS * WY AS Soe
* Sf ne - eS é Wa Ss bet A ZA . barren in the "2" ars
i), i fiZ Wie rig ZZ
immediate vicinity of the glacier. ahere are straggling trees high on the valley wall at the
e nd of the FIG. 43. EAST PART OF FRONT OF YALE GLACIER.
° Shows position of front in 1899 in relation to a tributary from the east. glacier, but ™
they do not come down close to the ice. An excellent ' photograph of the glacier is reproduced at page 128 in volume i. It is enlarged from negative 113, U.S. Biolog- ical Survey. A nearer view of the eastern part of the front (fig. 43), although lacking detail at the critical point, may serve a purpose for comparison when the gla- cier shall be revisited. It shows a small tributary, cas- cading from a hanging valley near the end of the main glacier.
84 ALASKA GLACIERS
The Harvard Glacier is by far the greatest discharging to the fiord. Only a few miles of it are visible from the sea, as the main trunk, traced backwards, curves to the right and disappears. So far as visible it is of low grade, its slope being gentler than that of any other we saw ex- cept the Muir and Columbia; and this feature, taken in conjunction with the notable height of the cliff in which it terminates (350 feet), indicates great depth of the ice stream andaremote source. The large number of medial moraines tells us that it has many branches, and five are visible from the sea. One from the southeast joins within a mile or two of the end, and the other four come from the northwest and north. All have steep grades in ap- proaching the main trunk, but two at least show gentler grades at higher altitudes. The Radcliffe joins the Har- vard so close to the water front that it does not become fully merged with the greater stream, but merely coalesces at one edge on its way to the sea. A conspicuous medial moraine of the Radcliffe maintains its high declivity quite to the water’s edge, and the cliff where the Radcliffe ends is notably lower than the confluent cliff along the front of the Harvard. The next tributary is likewise characterized by a strong medial moraine, and the branch- ing from which this arises can be seen a short distance back from its junction with the Harvard. The photo- graphs show no trees in close proximity to the Harvard. . The point of land at the branch in the fiord five or six miles to the south is forested, and this forest follows the coast for some distance toward the glacier, but stops sev- eral miles from its front. The opposite coast is reported free from trees at the water’s edge for eight or ten miles, but at an altitude of several hundred feet the trees ap- proach the glacier. These relations, while they do not show whether the glacier is now waxing or waning, indi- cate that its length has been several miles greater at a
Ww ie 2) *}J9| PTUII} Xd 9} 3B ‘AYTOpeA JY} SIOMIVN B P2ATId9I SBT YIM ou ATMO dy} JIISIA SaTIVINGLI} INoy 94} JO ‘“STQISTA JOU St ‘3Y311 9Y} Je YUBISIP Ivy ‘IdTOvIS 9y} JO peoy oy, ‘“Ssaureioul [Blpeut ye913 3} Ye YSIy y9J OSE st pu ‘apIM SajIM OA} ULY} DION ST PINS [Vpl} SIT “Jofovl[s oy} Wol sojtw Ussvs pNogsB ‘19}eM JY} WO ST IoAIISqO OL,
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86 ALASKA GLACIERS
period so recent that the forest has not yet reoccupied the abandoned ground.
As the Harvard has recently retreated more than its neighbors, and as its velocity is presumptively high, its future changes will have special value as indices of the local variations in the conditions of glaciation, and the record of its magnitude in 1899 is therefore important. Unfortunately the party did not approach it closely, and the photographs are deficient in detail at critical points, but they will enable the future observer to recognize any change of important magnitude. The best available data for 1899 are contained in Curtis’s photograph No. 273, reproduced at page 72 in volume. The east end of the frontal cliff, as there shown, is not far (between 1,000 and 2,000 feet) from the apex of a delta, or alluvial fan, built by the stream from a small hanging glacier. It is also seen that the eastern part of the glacier cascades about a half mile from the front, dropping so low that its tidal cliff has only half the height of that of the central part. At the west the relation of the Harvard to the Radcliffe is manifestly sensitive to the influence of advance or re- treat. A moderate recession would separate the two glaciers; an advance would deflect the lower part of the Radcliffe medial moraine into parallelism with the Har- vard medials (see fig. 44).
Smith Glacier reaches the fiord three or four miles from | the Radcliffe, and is of the same order of magnitude. Fed by several tributaries among the crests of the range, it gathers in a high mountain valley and then descends in magnificent cascades down the mountain front to the sea. In the last part of its course it has scarcely any valley, the outer surface of the ice being practically flush with the face of the mountain; and there is no flattening of its profile as it reaches the water. Though its lower slope is so seamed by crevasses as to exhibit a mere congeries of
87
COLLEGE FIORD
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24} pus ‘sapeosvo d01 ayT]-dajs aq} ase SaIN}Vdy DSI}OVIVYD ‘plvarey 9y4 Sururof ‘agropeyY ay} usy} pues ‘yIUIS 9y} U9} ‘IaTOBIH IMB UAIG SI 7J2T PT}
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88 ALASKA GLACIERS
pinnacles, two lines of medial moraines are distinctly traceable, each partitioning off a fourth part of the ice stream at the side.
The Bryn Mawr, next south of the Smith, is somewhat larger. Its two main branches, gathering in mountain val- leys not well seen from the sea, become visible in twin cascades, and then, uniting their streams, make a second leap to the sea. As tide is reached, there is a tendency to flatten the profile, and the central portion of the stream becomes nearly or quite horizontal for a few hundred feet before breaking off in the terminal cliff.
Next in the series comes the Vassar, parallel to the Smith and Bryn Mawr and exhibiting a similar series of cascades, but of smaller size and less direct in its course. It is cumbered, especially in its lower part, by rock débris, and close inspection was necessary to determine the fact that it was actually tidal.
The Wellesley, last of the tidal series, flows with gentle grade through a mountain trough joining the fiord at right angles, and then cascades to the sea, into which it plunges without notable modification of profile. Beyond it are small glaciers occupying alcoves on the mountain front but ending far above the water.
The Bryn Mawr, Smith and Radcliffe are represented in fig. 45, the Bryn Mawr alone in the-frontispiece, and the Wellesley in a plate at page 122 of volume 1, from a pho- tograph by Merriam (No. 121, U.S. Biological Survey series). The Bryn Mawr was photographed at shorter range by Curtis (No. 276 A), but the view has not been reproduced.
In the intervals between the tidal glaciers just described there is no forest at the water’s edge, and the photographs reveal none at higher altitudes; but a little farther south the coast is forested, and the trees climb up a few hundred feet on the moraine heaps under the hanging glaciers.
HARRIMAN FIORD 89
They are separated from the ice, first by a broad belt of alders, and then by a barren zone. As the spruce forest in College Fiord nowhere stands close to the ice, but is separated by a barren zone, it seems fair to assume that the ice has occupied this zone so recently that the period since its shrinkage has not sufficed for reforesting; but no facts are recorded tending to show the nature of the changes immediately preceding our visit.
The four tidal glaciers on the northwest side of the fiord, and four branches of the Harvard reaching it from the same mountain range, show a remarkable agreement in certain general features of profile. Near their dé- bouchure they descend in one or more steep cascades through a vertical space of 1,700 to 3,000 feet, and back of these cascades their slopes are comparatively gentle. Their upper valleys are deeply incised, but their lower valleys are shallow, barely sufficing to hold the ice streams, so that the faces of the glaciers are nearly flush with the general face of the fiord wall. These features indicate that the principal work of ice sculpture was per- formed when the trunk glacier filled the fiord to a level somewhat above the line of cascades. It was then that the fiord wall received its smooth contours, and much of the general excavation of the fiord may have been per- formed at the same time. The tributary ice streams from the side carved shallower troughs, adjusted to their needs, and were prevented from excavating deeply at any point because the great trunk glacier gave them a high base- level of discharge. These tributary troughs will receive further consideration in the chapter on Pleistocene glacia-
tion. HARRIMAN FIORD
From the bend where it is joined by College Fiord Port Wells extends only three or four miles northward and is reduced in width. Its trough then swings quickly
go ALASKA GLACIERS
to the west and southwest and is continued twelve miles farther. At the apex of the turn a large glacier (the Barry) protrudes from the northern shore, reducing the waterway to a narrow strait. The portion above the strait, having been discovered by the Harriman Expedi- tion, was named Harriman Fiord. The general width of the fiord is from two to three miles. Considered as a mountain trough, it branches near the middle, but the western branch is almost wholly occupied by a gla- cier. Its walls are everywhere high, and it is in fact a secluded pocket among the mountains. All about are glaciers, of which four are of large size and six reach the sea.
Barry Glacier (fig. 46), at the entrance to the fiord, approaches from the north-northeast. Its low grade indi- cates a distant source, but the source was not seen, as its upper valley was concealed by mist. Unfor- tunately the map data se- cured do not afford an ac-
The glacier comes from behind the dark hill at the right. The visible tributary descends by two cascades. Doran Strait lies be- curate deter- tween the glacier front and the sloping point of land at the left. : : . ati mination of
the dimensions of its end, but it impressed the beholder as one of the largest ice rivers of Port Wells. Its peculiar relation to the fiord causes it to be swept by the passing tide and prevents the accumulation of icebergs about its front, but the same relation exposes it to exceptionally rapid melting by the sea, and the conflict of ice current
BARRY GLACIER gI
with tidal current must be active. The forward flow of the ice tends to narrow the strait, and this constriction, by increasing the speed of the tide, enhances the melting power of the water. The fact that the glacier was able to occupy two-thirds of the width of the fiord indicates that its forward movement was strong.
= NN gi
os Mit } f} fiegd ios Wy ys ot ve ip Ay “i ~ Oh EL
FIG. 47- PART OF FRONT OF BARRY GLACIER. Showing the relation of a medial moraine toa great oblique dirt band. Photographed by
E. H. Harriman from the ship, June, 1899.
Its moraines were of small relative importance, but a belt along the western margin was darkened by drift and there were two medials. One of the latter, exhibited in
section in _ ric. 48. CAVES IN FRONTAL CLIFF OF BARRY GLACIER. the face of From a photograph by W. R, Coe.
the cliff, was seen to be the surface outcrop of a sheet of drift-charged ice which extended obliquely down- ward, passing under the western portion of the stream (see fig. 47).
The cliff was further diversified by a number of caves at the water’s edge, supposed to be the mouths of englacial streams.
92 ALASKA GLACIERS
Connected with the eastern edge of the ice was a long, narrow tongue attached to the shore (fig. 49), evidently a remnant left by the glacier at some very recent date when its front was more extensive. As this strip was not pro- tected by gravel, it must have been wasting rapidly, and the period of its separation may have been only a few months. I was in doubt whether to ascribe it to a pro- gressive shrinkage of the glacier or to seasonal variation.
Gi : ey GZ
. %
FIG. 49. EAST PART OF FRONT OF BARRY GLACIER.
Showing associated remnant of stagnantice. From a photograph by D. G. Inverarity. On the same coast the forest did not approach the glacier closely at the water line, but passed above it, leaving a barren zone several hundred feet broad. The common boundary of the barren zone and forest was so well defined as to indicate that it represented a former limit of the ice, but there were no overturned trees. If the forest ever occupied the barren zone, and was there destroyed by an advance of the glacier, the occurrence was so long ago that the overturned tree trunks had disappeared through decay. The portions of the forest nearest the ice included no trees of large size, but as there were many standing dead trunks it is probable that the growth was mature and that the small size of the trees indicated merely conditions un-
SERPENTINE GLACIER 93
favorable to luxuriant growth. Translating these facts into terms of glacial history, it seems probable that the Barry had been, at some time within the century, somewhat larger than when we saw it, but that it had not for a series of centuries exceeded the limit marked out by the neigh- boring forest. If any change had occurred within the last year or two it was of diminution.
The opposite wall of the fiord is forested down to the water’s edge, and it is thus shown that no recent advance of the glacier has carried it completely across the channel.
Next west of the Barry is Serpentine Glacier, coming down to the fiord from the north. It is a broad stream, of low grade, fed by four or five tributaries de- scending steeply from amphithea- _ ters in the encir- cling mountains. Though it reaches the sea, it yields few bergs, but is building a mo- raine barrier along most of its front. Its medial and lateral moraines are conspicuous, especially the north- ern lateral. Like the Turner and Reid, it seems to rest on a valley floor considerably above the floor of the fiord to which it is tributary. Its most westerly branch (fig. 50) heads in a high valley not fully commanded from the fiord and falls to the main glacier in two fine cascades. At the level of the upper cascade, 3,000 to 4,000 feet above tide, are three hanging glaciers, perched in alcoves of the valley wall where it curves to join the wall of the fiord.
FIG. 50. SERPENTINE GLACIER. The main body of glacier lies behind the nearer hill at right.
94 ALASKA GLACIERS
The only observed fact bearing on its recent history of change is the absence of trees from the valley walls - near it.
Two of the hanging glaciers are shown, at the left, in figure 50. The cascading tributary and other branches of the sien appear at page 124 of volume I, in a
ae : | al iM | ee i oe so fst " a y H ‘ ig ass Nd io CDi BE ne SEO ; = < ee = , Ss <@ 3 c Ga j y Z Wj
plate repro- ducing photo- graph No. 292 of Curtis’s series. Surprise Glacier reach-
a £U
FIG. 51. SURPRISE AND CATARACT GLACIERS. es the fiord Surprise Glacier (at right) has its source in a valley system be- from the west,
yond Cataract Glacier. and occupies a deep and long branch valley. Its sources were not visible, being concealed by the curvature of its valley, but its moderate grade and the lofty ice cliff in which it ends, mark it as an important ice river.
Its near neighbor, Cataract Glacier, occupies a narrow and lofty mountain trough, from the end of which it sends a steep, tapering tongue down to the sea. It is interme- diate in type between the hanging glaciers of the Ser- pentine valley and the cascading glaciers of the west wall of College Fiord.
The valley containing Harriman Glacier is a continua- tion of the main trough of the fiord and holds the same general southwest trend. The glacier curves toward the west and then toward the south, disappearing from view at a distance of nearly ten miles. As the most distant portion seen has a gentle slope and lies far below the bordering mountains, it is probable that the sources are still several miles beyond. Its general width is about a mile and a half, but its high-grade tributaries are so thick-
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EXPLANATION OF PLATE XV
| HARRIMAN GLACIER
The Upper Figure shows the south end of the frontal cliff of the glacier and adjoining parts of the valley wall. The main part of the glacier lies outside the view at the right (see plate x1). At the left: a tributary glacier descends from the mountain, and there are glimpses of other tributaries farther to the right. The visible part of the Har- riman Glacier is probably a motionless remnant, left clinging to the valley side by a slight retreat of the central part of the frontal cliff. See pages 94—96.
From a photograph made by D. G. Inverarity, June 27, 1899. Negative No. 286 of the Curtis series.
The Lower Figure shows the north end of the frontal cliff and ad- joining parts of the northwest wall of the valley. High on the moun- tain are two hanging valleys, each with a small glacier. See pages 95 and 119.
From a photograph made by D. G. Inverarity, June 27, 1899. Negative No. 285a of the Curtis series.
H.A.E. VOL.I
= >
I
PLATE XV
HARRIMAN GLACIER
SOUTH END OF FRONTAL. CLIFF
7 a - @- . =a? oo a ™ a * - Sieh oak - Sie ea ent Pt te: =~he
PHOTOGRAPHS BY CURTIS
HARRIMAN GLACIER
NORTH END OF FRONTAL CLIFF
t { ’ he. DA . ' t ‘ an ‘
Bus Hut y tf LG AD le PY
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MEM TN Rel ' qs ti va i,
4 ‘ i j y 7 fat : Ces 5 f d & ny) 7 . q % yy tip Peary f fal rity ) Welt matt - bite SSE MeN UT eee ll Pal t ‘ ‘ v rae tha is n IN ‘ < 4 i h ” wy ‘ ‘A x Ay # Fay oe e* Poy hs ‘ N % i [2 var Fou { c ' é i A TOS ne 1 ‘ 23 ' . i eo 7 wit ay: { ‘ J te : i > uw J i i ‘ : \ ? 1) « ‘ ; oo f r° ae j : *) 2h 4 ‘A i ‘ ; t ee ee i : y buf - i
HARRIMAN GLACIER 95
set as practically to coalesce, especially on the south- east side, giving a broad expanse of nearly continuous ice and névé. This expanse, fully commanded from the water, makes the view of the glacier a most im- pressive spectacle.
The visible moraines are few and unimportant, but the presence of much embedded drift is suggested by a detrital bank on which the eastern edge of the ice is seen to rest at the front. Above this bank the frontal cliff is low and irregular, but elsewhere it is lofty, ranging in height from 200 to 300 feet. From such a cliff an active discharge of bergs might be assumed, but our parties encountered only a moderate quantity of floating ice near the head of the fiord.
The glacier is not closely approached by forest growth, but shrubs were seen on the shore of the fiord within a few hundred yards of the ice. If the ice is diminishing, the recent retreat of the glacier front would appear not to have been rapid. The condition of the front in June, 1899, is recorded in a series of photographs. Two of these, reproduced in plate xv, show the ends of the frontal cliff, where the ice adjoins the valley walls, and will be serviceable for future comparisons with reference to ad- vance or retreat. A third (Curtis negative No. 291), published in volume I at page 74, gives a distant view of the glacier and its southeastern tributaries; and a fourth (Harriman negative No. 98), appearing in volume 1 at page 262, gives the glacier and its surroundings from a somewhat nearer point.
Some of the minor glaciers associated with the Harri- man occupy elevated valleys far above the main trough, and these upland valleys probably constitute a system initiated at an earlier epoch, when the fiord was flooded with ice to a great depth. [Illustrative examples are afforded by two hanging glaciers overlooking the lower
96 ALASKA GLACIERS
part of the Harriman from the northwest (pl. xv). No measurements were made, but it is evident from an inspec- tion of photographs that the heights of such features in this neighborhood are approximately the same as in the vicinity of Serpentine and Surprise glaciers, and it is possible that a number of minor glaciers observed on both sides of the fiord constitute with these a general system. Roaring Glacier, between the Cataract and the Harriman, owes the peculiarity suggesting its name to an abrupt change of grade. From a comparatively gentle slope it © passes to one so steep that loose masses find no lodgment, and as its movement steadily projects its end beyond the point of inflection, fragments of ice break away and tumble down the steep incline, to gather in a heap far below, where they lie until melted.
The condition of extreme glaciation to which these phe- nomena point does not belong to the series of modern changes, and will be referred to again in the chapter on the Pleistocene history. Were it of comparatively recent date the fiord would now be destitute of trees, but such is not the fact. It is true that the slopes are bare in the immediate vicinity of the glaciers, and that the valley walls enclosing the greater glaciers—the Barry, Serpen- tine, Surprise and Harriman— support no trees, but the lower parts of the fiord walls are elsewhere covered by a hemlock forest. .
As to the proper interpretation of the peculiarities of forest distribution the case is not altogether clear. In other localities there has seemed good reason to ascribe absence of forest to recent occupation by ice, but here there is a sort of transition from forest to barren which suggests climatic limitation. In the zone of transition the trees are not young and vigorous, as when invading newly- acquired territory, but scrawny and ill-favored, as though struggling desperately against the attack of hostile condi-
GREWINGK GLACIER 97
tions. In the accompanying illustration, representing the edge of the forest nearest to Harriman Glacier, the rareness a
of branches on the side toward the water sug- gests that winter fogs driven land- ward over- whelm the wee : boughs with EE EE ee
loads of ice. FIG. 52. HEMLOCKS BORDERING HARRIMAN FIORD.
, oe
— ° [Esper tc
GREWINGK GLACIER
West of Prince William Sound we saw glaciers in abundance —on Kenai and Alaska peninsulas and on Unimak and Unalaska islands — but only one was visited or approached so closely as to permit the making of ob- servations worthy of record.
The Grewingk Glacier is one of a series descending the northwest slope of the mountainous Kenai Peninsula. It was mapped by Dall in 1880, and revisited in 1895, when he made accurate note of the position of the ice front with reference to an object on the southern wall of the valley. In 1899 he accompanied me to the edge of the glacier for the purpose of pointing out this object, and I made a few photographs and other observations to aid in the recog- nition of future changes.
The glacier descends with moderate grade from a high névé, and maintains in its lower part a width of one and one-third miles. Its front is three miles from the sea, the interval being occupied by a gravel plain. For half the
98 ALASKA GLACIERS
distance the plain is bounded at the sides by rock walls, continuous with those containing the glacier, but these end at the general line of coast, and the plain flares beyond them as a low, broad cape. It is in fact a delta of glacial detritus, filling the lower part of the glacier trough and encroaching on the bay. The building of the plain is rapid. Its upper part was almost barren, as we saw it, only supporting enough scattered young spruces to show that their spread was not absolutely prohibited by soil or climate. Lower down were plantations of vigorous young cottonwoods, but no mature groves were seen. Border- ing lands of earlier origin are covered by spruce forest, and in places the growing gravel deposit was evidently invading the forest, overwhelming the undergrowth and burying the roots of large trees so that they languished and died. I was impressed with the fact that the quantity of rock waste discharged by the glacier was much greater than would normally be discharged by a stream of water draining a similar area.
The glacier bore no large moraines, and its generous output of rock waste must have been supplied chiefly by the englacial drift. The visible belt of this drift was broad at one or two points, but in general so narrow as to give the impression that the base of the ice lay consider- ably below the level of the gravel plain. The ice front was steep, probably ranging from 20° to 30°, and im- pressed Dall as much steeper than in 1895. It was de- cidedly steeper than the front of Hidden Glacier and the north front of the Hugh Miller, observed a month earlier, but less steep than non-tidal portions of the Columbia. If the correlation of high and low frontal slopes with ad- vance and retreat is well founded, the Columbia and Grewingk glaciers were advancing in 1899 and the Hid- den and Hugh Miller were retreating. If the slopes are related to the direction of the sun, those toward the south
GREWINGK GLACIER
4
eo Aa
at t?
aq
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net Wats
GREWINGK GLACIER, GENERAL VIEW FROM THE WEST IN 1899.
FIG. 53.
The north edge of the ice (at left) is seen to be separated from the forest by a belt of bare rock. The corresponding feature on the south is shown in figure 54.
\o \o
I0O ALASKA GLACIERS
are steeper than those toward the north. Close to the ice front the plain was interrupted by a low ridge of gravel (see fig. 54), a push-moraine associated with some small
ns fetes. Pee
bas eae Ne ie ae = " rr Me. RNR Rag SA 2 § MEER gS + a Ss
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FIG. 54. SOUTH WALL OF VALLEY AT FRONT OF GREWINGK GLACIER.
and recent advance of the glacier, and possibly a phenom- enon of the annual oscillation of the front. Farther out on the plain the course of a much larger moraine was marked by a crescentic line of mounds and short ridges, remnants of a once continuous morainic rampart that had been breached at many points by streams from the gla- ciers. I judged that this also was a pushed-up ridge, resulting from a plowing of the gravel deposit during a rapid advance of the glacier. It was not strictly parallel to the ice front in 1899, nor to its outline as mapped in 1880, but was more convex downstream. Its middle part was 2,600 feet from the glacier in 1899, and its most southerly remnant 800 feet. In 1880 Dall observed a considerable amount of ice under the sand and gravel of these mounds, and I noted many kettle-holes resulting from recent melting of ice remnants under the gravel
GREWINGK GLACIER IOI
plain inside the crescent. It is therefore probable that the advance occurred only a few decades ago.
Between 1880 and 1895 the ice retreated through a space estimated by Dall at 250 feet. Between 1895 and 1899 the portion of the front adjacent to the south wall of the valley retreated 350 feet. It happened that all of the observations were made in the same month, so that the re- corded changes were independent of seasonal fluctuations.
Figure 54, representing the south wall of the valley at the front of the glacier, shows the position of the ice on July 21, 1899. The gravel plain and the inner push-mo- raine occupy the foreground. At the extreme right a low boss of rock juts from the valley wall into the gravel plain, and just to the left of it is a large boulder resting on a drift terrace. On July 29, 1895, Dall found barely space to pass between the glacier and this boulder.
The same view shows the barren zone of the valley side and the lower limit of the forest, and the correspond- ing features for the north side of the glacier are seen at the left in the general view of the glacier, figure 53. At the south the line of forest was about 200 feet above the edge (1899) and descended westward to the gravel plain in 800 feet. For some distance below the line scat- tering young spruces and other bushes were seen, and even within the tract uncovered since 1895 a few alders had started. Nevertheless, the line of forest was clearly defined, being the lower limit of mature trees, dead trees, and accumulated humus. Though the line was unques- tionably caused by an advance of the ice, it was not marked by heaps of overturned trees, as at the La Pe- rouse and Columbia glaciers.
From these various phenomena a number of inferences may be drawn: (1) For several centuries — the age of the forest, including its dead trees—the glacier has not ex- tended beyond the lower limit of the forest; that is, it
102 ALASKA GLACIERS
has not very greatly exceeded its present size. During that period it may or may not have been much smaller than now. (2) During the latter part of that period the glacier advanced to the forest line and then retreated. This maximum probably occurred as much as fifty years ago—to allow for the disappearance of the overturned trees— but could hardly have been so early as the begin- ning of the nineteenth century, else there would be larger spruces below the forest line. (3) Several decades ago there was a maximum, affecting especially the central part of the glacier, and retreat from this was still in progress to the close of the century.
There was little difference in the extent of the two maxima, and although their separateness was not doubted during my visit, it now seems to me possible that the two were identical. One was inferred wholly from the fea- tures of the valley wall, and the other wholly from the frontal moraine. The straggling of young spruces below the forest line afforded so strong a contrast to the absolute barrenness of the morainic mounds that the possibility of connecting the two groups of phenomena with the same event did not occur to me; but Dall’s observation of ice remnants in the moraine in 1880 suggests a local cause for the sterility of the gravel mounds and leaves the matter in doubt.
SUMMARY OF MODERN CHANGES
During the last twenty years much attention has been given to the variations of glaciers, and a large body of facts has been collected, especially with reference to European examples. In attempts to generalize these facts serious difficulties have been encountered, and their discussion has not yet resulted in a satisfactory theory of the causes of change. All students of the subject feel the need of more extended observation, and from the point of
MODERN CHANGES 103
view of the theorist there is special interest in the history of changes in regions remote from those which have here- tofore received chief attention. Comparatively little is known of the history of American glaciers, but the avail- able data have been carefully collated by Russell’ and Reid,’ and an important contribution has recently been made by Klotz.®
The local descriptions of the preceding pages contain the additional observations made by the Harriman Ex- pedition, together with inferences as to modern changes; but as the paragraphs on variations are somewhat scat- tered, the principal inferences are here assembled in ré- sumé. The geographic order, from east to west, is re- tained.
In Glacier Bay the observations pertain to a large area, containing at the present time a considerable number of separate trunk glaciers. The data concerning variations are not equally full in all parts, but so far as comparable they are harmonious. It is probable that the history of the whole district centering in the bay is a unit. The history begins with an epoch when the glaciers were smaller than now. During this epoch a forest grew to maturity and then was overwhelmed by gravelly waste from the ice; the epoch was therefore measured by centuries. The glaciers then advanced many miles, attaining a maximum one hundred or one hundred and fifty years ago, and they have since retreated. Measured to the Muir Glacier, the total retreat to 1899 was more than fifteen miles; meas- ured to the Grand Pacific, it was more than thirty-five
1 Climatic Changes indicated by the Glaciers of North America: Am. Geol., vol. 1x, pp. 322-336, 1892. Reprinted, with little change, as chapter vim of Glaciers of North America.
2 Variations of Glaciers: Jour. Geol., vol. 111, pp. 278-288, 1895; vol. v, pp. 378-383, 1897; vol. vi, pp. 473-476, 1898; vol. vir, pp. 217-225, 1899; vol. VIII, pp. 154-159, 1900; vol. Ix, pp. 250-254, 1901; vol. x, pp. 313-317, 1902.
8 Notes on Glaciers of southeastern Alaska and adjoining territory. By Otto J. Klotz. Geog. Jour., vol. xIv, pp. 523-534, 1899.
104 ALASKA GLACIERS
miles. The retreat was interrupted by a temporary ad- vance between 1890 and 1892. |
La Perouse Glacier is practically at maximum now. It has not been greater for centuries, except that it was a little longer a few years ago, when it invaded a mature forest. As its neighbors at the east and west were much smaller a century ago, analogy suggests that the present maximum was preceded by an important minimum.
In Disenchantment Bay and its dependencies a great retreat, amounting to at least five miles along one channel of outlet and thirty miles along another, has been in prog- ress for more than a hundred years. There is evidence of other changes, but their order and dates are unknown.
Columbia Glacier is practically at maximum now, and was nearly as large in 1794, but an important minimum probably occurred within the nineteenth century. It has not been greater than now for centuries, except that it was a little larger about the year 1892, when it invaded a mature forest.
The numerous glaciers of Port Wells, including College and Harriman fiords, may have a harmonious recent his- tory, but the data are too meager to warrant a definite state- ment. They are somewhat smaller than at a maximum which may have occurred fifty to one hundred years ago.
Grewingk Glacier has not for centuries been much larger than now. It was somewhat larger between fifty — and one hundred years ago, and may have had a subse- quent maximum of nearly the same extent.
The most conspicuous fact brought out by the compari- son of local histories is that they are dissimilar. Never- theless, there are limited resemblances. The Glacier Bay and Disenchantment Bay histories agree in including a great retreat, occupying more than a century. The Port Wells and Grewingk histories agree in a moderate retreat occupying something less thanacentury. The La Perouse
MODERN CHANGES 105
and Columbia histories agree in a present condition of maximum glaciation probably preceded by an important minimum.
As glaciers grouped together (about Glacier Bay, Dis- enchantment Bay, etc.) have seemed to vary in harmony, it is natural to look for a systematic geographic arrange- ment of the diverse histories; but such arrangement is not apparent. Port Wells and the Grewingk Glacier, inter- mediate in type of variation, are the most westerly of the localities (see nies fig. 55): Between Glacier nie and Disenchant- f= <== a ment Bay, rep- resenting one extreme of variation, flow La Perouse Glacier and its neighbors rep- resenting the opposite ex- treme. La Perouse and Columbia gla- ciers, agreeing Sota in phenomena FIG. 55. DISTRIBUTION OF GLACIER LOCALITIES.
Scale $9 O S80 100 60 200 250MILES SS eee ee
of variation, are separated by the contrasted phenomena of Disenchantment Bay.
Glacier Bay adjoins Lynn Canal, being separated only by a mountain range, and some of the high névé fields of this range feed glaciers of both slopes. On both sides the glaciers are believed to be retreating, but the front of the Davidson of Lynn Canal is less than half a mile from the forest on its old moraine, and the Muir of Glacier Bay is nearly twenty miles from the equivalent forest. The great Fairweather Range, separating Glacier Bay from the Gulf
106 ALASKA GLACIERS
of Alaska, nourishes many glaciers. Of these the Johns Hopkins, descending northeastward, has shared the great retreat of Glacier Bay; but the Brady, flowing south, and the La Perouse and Crillon and their neighbors, flowing southwest, have advanced during the same period.
Close to Disenchantment Bay lies the Malaspina, a pied- mont glacier fed by alpine glaciers of the St. Elias Range. From other slopes of the same range come the principal feeders of the Hubbard, the main glacier of Disenchant- ment Bay. Inacentury or two the Hubbard has retreated five miles up Disenchantment Bay, but the Malaspina is bordered in places by a mature forest from which it has retired only a short distance, and at one point it has even advanced against the forest within a few years.’
The general fact appears to be that mere proximity does not ensure parallelism of glacial history; on opposite sides of a mountain range the sequences of change may be not only different but antithetic.
THEORIES
In the discussion of the causes of the advance and retreat of European glaciers the phenomenon occasioning greatest difficulty is the lack of parallelism between the variations of different glaciers and different groups of gla- ciers. The histories of glaciers of the Alps exhibit dis- parities similar to those of Alaska, with the apparent . difference that the Alaskan disparities are of larger scale, just as the Alaskan glaciation has a larger pattern; and the arctic and boreal glaciers of Europe probably exhibit equal irregularity, although Rabot, who has recently assembled the evidence, finds a number of partial corre- spondences.’
1]. C. Russell. Amer. Geol., vol. rx, p. 329, 1892.
2 Les variations de longueur des glaciers dans les régions artiques et boréales. Arch. des Sci. Phys. et Nat., 4me periode, vols. 3, 7, 8, 9, Geneva, 1897-1900.
CAUSE OF VARIATIONS 107
For the explanation of irregularity there are two promi- nent hypotheses. The first, regarding oscillation of long period as climatic, ascribes minor oscillations to the rhythmic gorging and disgorging of the névé reservoir. The rhythmic period, being connected with topographic conditions, is different in different glaciers.
The second, which has been more fully developed, ap- _ peals to the principle of lag. The chief cause of variation of the wasting end of the glacier is believed to reside in variation of snow accumulation on the névé fields, but con- siderable time is required for the transmission of the effect from end to end of the glacier. For average Alpine glaciers this time is believed to amount to several decades, but it varies with the length, slope, and other peculiarities of the individual ice streams, and the general result of its variation is that ice streams of the same mountain slope, or streams flowing from the same névé, initiate a period of advance or retreat in different years or even different decades.
It is impossible to compare the first hypothesis with the behavior of Alaska glaciers, on account of the meagerness of observational data. As yet we know nothing of perio- dicity of variation. The comparison of the second is ob- structed by the lack of meteorologic records for the glacier region, and by the fact that very few of the determinations of variations are associated with definite dates; no com- parison with climatic variation is possible, and the com- parison of individual histories of variation, one with another, is approximate only. Nevertheless, some judg- ment may be formed of the general competence of the second theory; and it seems to me not fully adequate for the explanation of Alaskan disparities.
Consider, for example, the contrasted histories on oppo- site sides of Fairweather Range. On the northeast slope a great advance culminated not less than one hundred
108 ALASKA GLACIERS
years ago, and a great retreat has been in progress ever since. On the south and southwest slopes the same period of one hundred years has witnessed a general advance. The century’s variation for one side of the range, in a general way and so far as known, is the reverse of the va- riation for the other side. ‘To apply the principle of lag to the phenomena it is necessary to suppose that the glaciers of one slope are very far behind those of the other in some phase of variation. If the southwestern group are con- sidered the slower to respond to variations of névé supply, the inference is that they are now at or near a culmination corresponding to the culmination of the northeastern group a century or more ago. If the northeastern group are considered the slower to respond, the inference is that though now at very low ebb, they have not yet felt the impulse which has carried the southwestern group to a maximum; and many decades, if not a full century, will be required to bring them to the same phase. It is not clear to me which horn of the dilemma should be taken, but in either case the time interval between corresponding phases is greater than can reasonably be ascribed to lag.
Associated with the theory of lag as applied to the variations of European glaciers is a generalization that glacial variation is rhythmic, with a period of about thirty- five years, each recurrent cycle of variation being brought about by a corresponding cycle of climatic change. In this respect also the Alaskan phenomena are discordant. It is not credible that the great advance and retreat which occurred in Glacier Bay, involving the extension of glaciers along the main trough for thirty-five miles, or more, and their subsequent melting, could be accomplished in so short a period as thirty-five years; for, though direct ob- servation has covered but a small part of the great oscil- lation, it has shown that in the half of thirty-five years the retreat of the ice front was less than five miles.
CAUSE OF VARIATIONS 10g
Reid has suggested a local subsidence of the land as a possible explanation of the retreat of the glaciers of Glacier Bay.’ Stumps of trees that grew in Muir Inlet before the great advance of the glacier, now stand at low- tide level, and demonstrate a submergence of at least twenty feet. The submergence may have been greater; and he points out that any lowering of the surrounding land with reference to the sea would make the conditions less favorable for the accumulation of snow and tend to reduce glaciers. ‘To extend this explanation so as to cover the diversity of local histories it would be necessary to assume that the Fairweather Range was not lowered in company with the adjacent tract about Glacier Bay; and it would be logical also to assume that the great ex- pansion of Glacier Bay ice which preceded its shrinkage was associated with a rise of the surrounding land. As there is independent ground for believing that the region is one of active mountain growth, the occurrence of such differential and diverse movements is quite conceivable, and their possibility should be kept in view in the study of each locality. But as glaciers are highly sensitive to climatic changes, as climates are subject to continual and rapid variation, and as earth movements are comparatively slow and moderate in their influence, the central theory of glacier variation is necessarily climatic rather than diastrophic.
With reference to the climatic explanation of the Alaskan phenomena I have a suggestion to contribute —a sugges- tion of a somewhat vague character, not yet reduced to the form of a definite hypothesis. It is, that the combi- nation of a climatic change of a general character with local conditions of varied character, may result in local glacier variations which are not only unequal but op- posite.
1Nat. Geog. Mag., vol. Iv, p. 40, 1892.
IIo ALASKA GLACIERS
The general drift of the suggestion may be illustrated by considering some of the more evident consequences of an assumed change in the temperature of the water of the Gulf of Alaska. Let us assume that the water becomes warmer, and that all other factors affecting glaciation remain unchanged. ‘The consequences would include:
1. A higher temperature for the air currents flowing from the gulf to the land.
2. A greater contrast in temperature between the coastal belt and the interior of Alaska, especially in winter.
3. Greater evaporation from the ocean and a higher humidity for the landward-flowing air — resulting from 1.
4. Greater precipitation on the mountains, especially in winter — resulting from 2 and 3. :
5. A shorter annual period in which precipitation takes the form of snow—resulting from 1.
6. A (probably) lower ratio of snow to rain — resulting from 5, qualified by 4.
7. A higher snow-line.
8. More rapid waste of ice and snow by evaporation and melting —resulting from 1, 5 and 7.
Of these consequences, the increase of precipitation would tend to enlarge glaciers, while the lessened ratio of snow precipitation and the enhanced wasting would tend to reduce them.
Evidently a lowering of the temperature of the gulf water would be followed by the reverse consequences.
If the hypothetic rise of ocean temperature were carried to an extreme, the snow-line would be driven above the mountain tops and the glaciers would disappear. If the hypothetic fall of ocean temperature were carried to an extreme, so as to abolish the contrast between sea and land temperatures, the southern coast of Alaska would be reduced to the condition of the western coast, and glaciers would disappear from all but the highest mountains.
CAUSE OF VARIATIONS II!
There is, therefore, a temperature of ocean water which is more favorable for the development of glaciers in the coastal mountains than a higher or lower temperature. But this temperature is not the same for all parts of the coastal belt; it must vary with local topographic charac- ters. The glaciers of a low range may be more sensitive to variations of the snow-line than those of a high range. Glaciers facing the sea may be more sensitive to the variations of wastage dependent on the tempera- ture of the incoming winds than are glaciers facing the in- terior. Glaciers fed from cirques, where snow is concen- trated by wind and avalanche, may respond to variations of precipitation in a very different way from glaciers fed by open névé fields, where much of the annual snowfall is dissipated by dry evaporation. The laws of variation for high-grade glaciers may be quite different from those for glaciers of gentle slope. And so, when the ocean tem- perature approximates the value most favorable for the development of glaciers in the district as a whole, it will be too warm for the highest development of certain gla- ciers and glacier systems and too cool for others. And whenever such a condition obtains, a change in ocean temperature will cause some glaciers to enlarge and others to contract.
It is of course impossible that one of the meteorologic conditions determining Alaskan glaciation should vary by itself while all other conditions remain constant, and the case assumed for the sake of illustration is therefore purely ideal. It has served its purpose if it has given plausibility to the suggestion that a change in some meteorologic factor or factors may result in simultaneous modifications of glaciers which differ not only in amount but in algebraic sign.
Whatever may be the causes of the variations of gla- ciers, Alaska affords an inviting field for their investiga-
I1Iz2 ALASKA GLACIERS
tion. Intermediate in accessibility between the glacial districts of Europe and Greenland, it is more comprehen- sive than either in variety of local circumstance. The complexity of interacting conditions may for a long time baffle attempts at analysis, but when the complexity has been resolved, the resulting theory should have wider application than one founded on simpler phenomena.
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CHAPTER II PLEISTOCENE GLACIATION
ALL geologists who have studied the region we tra- versed are agreed that the glaciers were much more ex- tensive in Pleistocene time than now; but opinions dif- fer widely as to the actual magnitude of the ancient ice fields, and also as to the extent to which they modified the topography of the country. As the nature of my journey rendered my view somewhat cursory and superficial, and as nearly all parts of my route had been covered, with better opportunity, by one or more of my predecessors, I can not expect to settle any of the vexed questions, but it still seems best to make rather full record of my obser- vations and impressions. When an observer views a complex phenomenon his attention is naturally directed to the particular features which his previous training en- ables him to appreciate — he “sees what he has eyes to see”; and the difference of eyes makes the work of independently trained observers. more or less comple- mentary.
( 113 )
114 ALASKA GLACIERS
HANGING VALLEYS
Of the various classes of evidence from which the his- tory of Pleistocene glaciation is inferred, the physiographic is most available to observers who see the land chiefly from the deck of a vessel. Ice-scoured surfaces referable to the ancient glaciers were occasionally discovered during our journey, and a few drift deposits were closely exam- ined; but such observations served chiefly as checks on inferences from topographic form.
The general characters of the physiographic data which may be used in such studies are familiar and need not be recited here, but a special sculpture feature — the hanging valley — may need introduction to some of my readers. Its utility in the interpretation, discrimination and estima- tion of the work of Pleistocene glaciers has been little appreciated until quite recently,’ but in the study of the Alaska field it was found extremely useful.
A hanging valley is a small U-valley tributary to a larger valley, the floor of the smaller being considerably higher at the junction than the floor of the larger. Many of them are short, high-grade troughs, heading in cirques; some are mere cirques, without troughs — spoon-bowl hol- lows, high on the walls of main valleys. They are asso- ciated with other evidences of glacial sculpture, and the _elevation of their floors is believed to result, as a rule,
1 Lake Chelan, by Henry Gannett: Nat. Geog. Mag., vol. rx, pp. 417-428, 1897. Glacial erosion in the valley of the Ticino, by W. M. Davis: Appalachia, vol. IX, pp. 136-156, 1900. Glacial erosion in France, Switzerland and Norway, by
W. M. Davis: Proc. Boston Soc. Nat. Hist., vol. xxix, pp. 273-322, 1900. Review of the last by T. C. Chamberlin: Jour. Geol., vol. vin, pp. 568-573, 1900.
Davis’s second paper reviews the literature, points out that McGee, De Lap- parent and Richter had advanced somewhat similar ideas as to the origin of hanging valleys before the appearance of Gannett’s paper, and mentions an unpublished address by Penck. The glacial explanation of the hanging valleys of the Alps is opposed by Bonney and Garwood in Quart. Jour. Geol. Soc. London, vol. Lviu, pp. 690-718, 1902.
HANGING VALLEYS II5
from the unequal erosion of valleys by glaciers of un- equal size.
Where a trunk glacier of alpine type receives a rela- tively small lateral tributary the main ice stream gives base-level to the tributary. Their relation in this respect is homologous with the relation of main and tributary streams of water. If the magnitude of trunk and tribu- tary have remained constant long enough for erosion to bring about an adjustment of grades, the surface of the tributary at the point of junction has the same level as the adjacent surface of the trunk. But the bottoms of the two channels do not have the same level. The trunk stream is normally deeper than the tributary, and at their junction its bottom lies at a lower level. If the streams (of ice or water) be removed, the bottom of the tributary channel is found to end high up on the side of the main channel.
The ideal case, diagram- matically illustrated in figures 56 and 57, is also il- lustrated in the actual topo- graphy of couaaaes § regions FIGS. 56 AND 57. DIAGRAMS ILLUSTRA-
sculptured by Pleistocene TING ORIGIN OF HANGING VALLEYS.
laciers 56. A terrestrial block containing a trunk & ‘ glacier and tributary with well adjusted chan-
The hanging valley is es- els.
r - ? < 57. The same block without the ice, show- pecially significant in two _ ing the adjusted glacier channels, The trunk
li f h ° hi ° channel is deeper than the tributary; the trib- ines Of physiograpNic 1M gtary channel isa hanging valley on the side
terpretation. It is-a con- ‘he ‘unk channel.
spicuous earmark of the former presence of glaciers; and it helps to a conception of the magnitude of Pleistocene glacial erosion.
116 ALASKA GLACIERS
Its value as an earmark depends on the principle of exclusion; glaciation is the only physiographic process known to produce such forms. It is true that discordance of level between trunk and tributary valleys is not by itself — diagnostic of glaciation, for it often occurs as a temporary condition in systems of stream-made valleys, especially when fresh uplift stimulates down-cutting by -trunk streams; but in such cases discordance is associated with the narrow trenches of youthful or rejuvenated topog- raphy. It is true also that the glacial U-trough is some- times (though rarely) simulated by products of stream erosion, and that a hollow closely resembling the glacial cirque is occasionally produced by aqueous process; but these imitative forms belong to the middle life of a stream, when down-cutting has so slackened as to permit valleys to broaden, and they imply a harmonious grading of stream beds, inconsistent with discordance of level at the junc- tion of tributary and trunk. But the combination of dis- cordance of level with U-shaped cross-profiles constitutes a physiographic type peculiar to the work of glaciers.
The significance of the hanging valley for the valuation of glacial erosion depends largely on the assumption that
», the discordance of level was mae po produced by the glacial exca-
Soe vation of the main trough, and
3 this assumption requires qual- | ification. If ABC in the dia- FIG. 58, DIAGRAM ILLUSTRATING gram (fig. 58) be the cross- DISCORDANCE OF HANGINGVALLEYS. profile of a main glacial trough, DE the longitudinal profile of a tributary trough, and EF the produced floor of the tributary, the ‘discordance’ is rep- resented by the height of / above #. If the preglacial stream valleys were accordant in grade, their junction was at /, or some point above /; and FB is the meas- ure either of the deepening of the main trough by the
0) PRS
~
y
ead Wa TT y A a y « % iM i Paes o
me
4
1714
‘es walue as an earmark is on Rhe principle of ¢ exclusion; glaciation is the only. 1D ee * tic ro ess known to produce such forms. itis ty i pdliscordance ‘of level between trunk and tributary oe at by itse diagnostic of glaciation, for it often | fe . condition im systems of sreameamade 7 when fresh uplift stimulates © et streams; but.in such cases discordenay Weis the narrow trenches of youthful. or rep an ated topo raphy. It is true also that the glacial U-trough is some- ~ times (though rarely) simulated by products. ete ream erosion, and that a hollow closely renee hy: ried acial cirque is occasionally produced by aqueous f 58 3 mut 3 these imitative «forms belong t the middle ico a ream,
vy) oe
ie! a ae age” ee
~— rtm,
ficaGiort. + If aBCw ae | “ie ot | FIG. §8. canst iE: grasa. (6g 58) be the Sat DISCORDANCE OF MANGINGOVALLEYS. profite of a main glacial tr rough, eo DE the longitudinal profile of a tributary trough, an ¥ E, aie : the produced feor of the tributary, the ‘discordance’ is rep> - resented by the height of # above #. If the preiheail 4 stream valleys’ witre accordant in gradé, their junction —
sat &, or some point above 7; and #P is the meas= a eithe: of the deepening of- the main yee by the
H.A.E. VOLLIII PLATE XVI
eo |
A "HANGING VALLEY, FRASER REACH.
HANGING VALLEYS 117
glacier, or of the difference between that deepening and the deepening of the tributary. If the preglacial val- leys were discordant, the main valley must have been young, and was probably so narrow that its conversion into a U-trough involved much excavation at the sides. In either case, therefore, the occurrence of high hanging valleys is indicative of great erosion by ice.
Yet another qualification is necessary, for there is a special condition under which a relatively young stream valley may have the width of a glacial U-valley. When the activity of streams is revived by uplift, the general degradation may be outstripped not only by trunk streams but by strike streams following outcrops of weak rocks; and if the contrasts of rock resistance are great, a broad belt of weak rock may induce the development of an open valley or wide trough, while neighboring uplands of re- sistant rock are still little modified. ‘Thus may arise a topographic condition susceptible of conversion by only a moderate amount of subsequent ice work into a typical glacier trough with hanging valleys.
Theoretically, then, there are at least three cases to be borne in mind in inferring the quantity of glacial erosion from the existence of hanging valleys. First, the grades of preglacial streams may have been accordant, in which case the discordance of hanging valleys with trunk valleys yields a rough measure of the depth and amount of glacial erosion. Second, the grades of preglacial streams may have been discordant, and without dominant control of contrasted rock texture, in which case the erosive work of ice may have consisted chiefly in the enlargement of V-gorges to U-troughs. Third, the discordance of pre- glacial grades may have been associated with the rapid opening of valleys in weak rocks, in which case the erosive work of ice may have been small. The criteria for dis- criminating the three cases have not been worked out,
118 ALASKA GLACIERS
but a few general propositions may be advanced. In the first case a study of the district should discover independ- ent evidence of the maturity of the preglacial topography. In the second and third there should be independent evi- dence of rejuvenation of preglacial streams. The third could not arise unless the main troughs follow the strike.
The practical problem is further complicated by the fact that the type of initial topography, when determined, leads to only a limiting value for the total erosion, and also by the complexity of glacial history as dependent on climatic variation. A glacier which begins erosive work by broadening and rounding the cross-profile of a stream gorge does not cease activity when that result is attained. One which falls heir to a weak-rock strike valley, fairly adjusted to its conditions of flow, may carry the work of excavation far beyond the grade limit of the ancestral stream, and hollow out a lake basin or fiord trough. And the coordinated system of grades and channel forms toward which the erosive work of grouped glaciers tends, is itself modified by every change of the general volume of ice.
But despite all qualifications the hanging valley is the most important witness yet discovered to the magnitude of the work accomplished by the alpine glaciers of the Pleistocene.
The hanging valleys of Alaska are illustrated by many of the figures and plates of this volume. The mouth of one overlooking Hidden Glacier is imperfectly shown in plate v and figure 28, and an alpine valley truncated below by erosive action of the glacier appears in plate vi. Figure 30 shows the mouth of a hanging valley above Nunatak Fiord; a glacier issuing from a hanging valley north of Nunatak Glacier is shown in figure 31; and a glacier cas- cading from a hanging valley of the south side of the same trough in figure 32. Figure 43 shows a tributary to Yale Glacier issuing from a hanging valley, and figures 44
INLAND PASSAGES 1 fe)
and 45 a series of similar valleys and glaciers bordering College Fiord and Harvard Glacier. In figure 46 two hanging valleys are shown, the one empty, the other fur- nishing a tributary to Barry Glacier; in figure 50 are two high valleys with small glaciers overhanging Serpentine Glacier; and figure 51 represents Cataract Glacier, issuing from a high valley and cascading to Harriman Fiord. All . these examples, occurring in the preceding portion of this report, are incidentally included in views selected to illus- trate other features. In the following portion are a num- ber of views chosen wholly or partly with reference to hanging valleys; and the remark applies especially to plate xvi and to figures 62, 66, 69, 70, 71, 72, 74, 76, 77, 81, 88 and 93. THE DISTRICT OF INLAND PASSAGES
From Puget Sound, Washington, at the south, to Lynn Canal and Glacier Bay, Alaska, at the north, a space of goo miles, the coast of North America has a peculiar and significant facies. It is divided into a fringe of rugged peninsulas by deep, narrow inlets, and guarded from the surges of the open ocean by a great number of rocky islands and islets. In this respect it resembles the coast of Maine and the western coast of the Scandinavian pen- insula, and, like them, its peculiar characters are associ- ated with evidences of extensive glaciation. It differs from those coasts in the fact that some of its islands are of great extent, so as to include or be constituted by mountain ranges, and in this respect it is paralleled by a single district only, the western coast of the southern ex- tremity of South America.
The map of the district, figure 59, though drawn to so small a scale as to show only the larger islands and prin- cipal fiords, serves to illustrate the intricate penetration of the land by the sea. It is reduced from the large chart (3689) of the U. S. Coast Survey.
120 ALASKA GLACIERS
MAP
OF PART OF
\ THE WESTERN COAST ‘ or | NORTH AMERICA
: 8 HOWING ISLANDS.AND FIORDS
‘ Scale
o 80 100 iL En
sae ee “Be in ia) % A :
Bo
FIG. 59. FIORDS OF THE INLAND PASSAGE DISTRICT.
INLAND PASSAGES I2I
The general trend of the coast of the mainland is north- west to north-northwest, and this trend is shared by the longer axes of the principal islands. There are thirty-two islands exceeding twenty miles in their greater dimensions, the maps show more than 400 islands above one mile in extent, and the islets are uncounted.
With minor exception, the peninsulas and islands are mountainous, descending steeply to the water, and the passages between them are deep. Most of the inlets of the mainland and many of the passages dividing islands are of approxi- mately uniform width for long distances, and the parallel
shores of such linear water- 16-60. AN ALASKA FIORD; TRACY ARM, HOLKHAM BAY.
ways are usually steep and somewhat simple in contour. Repeating thus the characteristic features of the Norwe- gian coast, they fall within the physiographic class to which the name fiord is applied. The northwesterly trend char- acteristic of the islands affects also the passages between them, and has enabled navigation to select for its use a route close to the mainland, where deep waters are almost wholly protected by the islands from waves and storms of the open ocean. This route is commonly known as the‘ inside pas- sage.’ Our steamer followed it on both the outward and return voyages, our principal deviation from it being made by a visit to Sitka, which lies on the southwest or oceanic side of Baranof, one of the outer line of islands. Parts of the journey were made at night, but the outward and inward courses, taken together, showed us much the
I22 ALASKA GLACIERS
greater part of the inside passage, and our examinations about Sitka occupied several days. An excursion to White Pass gave a view of a canyon at the head of a fiord, and of uplands at 2,000 to 2,500 feet altitude, but the higher summits were seen only from stations at~-or near sea-level.
Direct observation of the uplands was afterward supple- mented by the study of photographs. The U. S. Coast and Geodetic Survey and the Canadian International Boundary Commission have used the camera freely in con- nection with topographic surveying, and I was so fortu- nate as to have access to their series of pictures. The latter organization spread a web of triangulation over all the mainland portion of southeastern Alaska, and from each of the mountain peaks occupied as stations photographed the entire horizon, using the views afterward for the con- struction of contour maps. Their album thus represents the upland in a systematic and thorough way and is emi- nently adapted to physiographic study. (See page 6.)
In this, as in other districts of Pleistocene glaciation, it is evident that the Pleistocene sculpture is superposed on an earlier sculpture, chiefly aqueous; and in the discus- sion of the work of Pleistocene glaciers it is necessary to consider the pre-Pleistocene condition. I find it conve- nient to begin with that consideration.
Pre-Pleistocene Topography
So far as we saw the indurated rocks, and so far as we know them from the descriptions of others, they are either igneous or metamorphic. The igneous rocks are almost wholly intrusive. The metamorphic exhibit various de- grees of alteration, but all are so folded or squeezed that the planes of structure make large angles with the hori- zon. ‘The general strike is believed to be parallel to the coast, but there are few direct observations of strike. In-
HIGH PENEPLAIN 123
ference rests partly on the trends of structure lines deter- mined by the Canadian Geological Survey in neighboring parts of the continent, partly on the trends of the straighter valleys and channels of the region itself.
From this complex the pre-Pleistocene topography was developed by erosion. The only constructional forms we saw which might have antedated the Ice Age were a few volcanic cones. The system of relief was related to three known base-levels. The plane of the first is now high in air, above some of the mountains and among the peaks of others. The second is not far from present sea-level, and the third is below sea-level.
The fligh Peneplain.— 'The uplands of the mainland are remarkably uniform in general height over large areas, not indeed presenting plain surfaces, but either exhibiting harmony of crest lines, despite profound and general dis- section, or else occupied by numerous small shallow val- leys, which are strongly contrasted with the deep steep- walled trenches of a less complete dissection. These features can be most readily presented in connection with some of the accompanying illustrations. Figures 3, 61, 62, 63, 75, and 77 were drawn from photographs by the Canadian Boundary Commission.
Figure 61 shows the upland topography north of the western end of Cross Sound. (The reader can identify the locality on the map, page 120, as the third cape west of the mouth of Glacier Bay.) We stand on a summit above Cape Spencer, and look northwest. At the left is the Pacific Ocean; in the center distance, the end of Fairweather Range (the nearest high peak being La Pe- rouse, 10,750 feet); at the right, Brady Glacier, its foot separated from Taylor Bay by a gravel strand. Between us and the base of the mountains, 18 miles away, are a series of hills somewhat uniform in height. The higher points (as we learn from the Commission’s contour map)
‘
124 ALASKA GLACIERS
range from 2,000 to 2,500 feet above tide, and near the mountain rise above 3,000 feet.
Viewing these hills collectively, one can hardly fail to be impressed with the appearance of system in their crest lines. Some of the hills have broad and flattish, or gently arched, backs; and all the higher parts of their profiles seem to belong to a single gently sloping plane. ~Should the valleys between them be filled up even with the crest lines, the group would become a plateau with undulating surface. It is natural for the geologist, when he sees such a harmonious arrangement of hill tops, to seek an explanation in the structure of the rocks, but in this case a structural explanation can not be found. The rock layers are not horizontal but nearly vertical, and they have been cut across in the shaping of the land. The local elements of the upland forms are due purely to erosion. The most probable explanation of the phenom- ena is that the area was first worn down to a plain at or near sea-level, afterward raised so as to be a plateau, and then dissected into a group of hills. The habit of the hills indicates that the principal work of dissection was by streams, but there was also glacial sculpture. They were overrun by the ice-sheet, and the glacial rounding of summit angles helped to obscure, though it failed to destroy, the evidence of the old base-level plain.
Yet other evidence of the geologic history is connected with the trends. The rock structure strikes northwest, or from the foreground toward the mountains, and this is also the trend of the upland as a whole. But the crests of individual hills trend east of north, making angles of 50° to 60° with the strike; and the separating valleys have the same trend. The valleys do not head against high summits among the hills, but traverse the plateau from side to side. They seem to be the work of a system of streams whose courses across the plateau were deter-
HIGH PENEPLAIN
UPLAND TOPOGRAPHY NEAR CAPE SPENCER.
FIG. 61.
A chain of hills carved from an original plateau. See page 123.
125
mined by some cause other than the rock struc- ture. As their direction coin- cides with that of the local in- clination of the old peneplain, it is highly proba- ble that they were super- posed on the rock structure at the time of the uplifting of the plateau. The great valley holding Brady Glacier and Tay- lor Bay, on the other hand, runs parallel to the strike of rocks exposed in the hills, and may fairly be as- sumed to occupy the outcrop of a belt of compara- tively weak rocks.
If now we project the sum- mit plane of the
126 ALASKA GLACIERS
hills backward across the Brady-Taylor valley, we find that it passes among the highest peaks of another and higher upland, an upland lacking the broad summits of the Cape Spencer hills, but characterized instead by notable uniformity in the height of numerous acute summits. A suggestion of this character may be seen at the right in figure 61.
Before leaving this view, note should be made of the fact that the peneplain of the Cape Spencer hills ends northward at the base of Fairweather Range. The range is distinct in physiographic type and in geologic history.
The reader is now asked to turn back to figure 3, drawn to give a bird’s-eye view of Davidson Glacier, but show- ing also the east wall of Lynn Canal. The point of view is not quite so high as the crest of the opposite wall, but is high enough to show that the upland bounded by that wall has plateau characters. There are none of the smooth crest lines seen in figure 61, but angular peaks and crests standing close to the mural face combine with angular peaks and crests farther back to give an even sky-line. All the valleys visible are upland valleys, and it is not hard to believe that these have been carved out of an uplifted block, the plane of whose original flat top runs among or above the phalanx of sharp summits.
This upland stands about 3,000 feet higher than the hills of Cape Spencer, and is eighty miles northeast of them. ‘The intervening uplands are parted by two great fiords, Lynn Canal and Glacier Bay, and are considerably dissected in detail, but where most massive they have the plateau habit shown in figure 3; and they are intermediate in height between the plateaus at east and west.
In figure 62 we have the view commanded from a peak like one of those against the sky in figure 3. The locality is twenty-five miles farther south, and we are looking eastward from a point about five miles east of Lynn Canal.
HIGH PENEPLAIN 127
The higher summits have a general altitude of 5,200 feet. It is now evident that the sculpture is that characteristic of the work of local glaciers. The sharp peaks overlook cirques, many of them still filled with ice; below the cirques are short glacier troughs; and between the troughs are narrow crests. These glacier troughs are not insig- nificant features—the beds of those in the field of view lie 1,000 to 2,500 feet below the plane of the high peaks — but they are so small in comparison with the great earth block from which they have been hewn that they do not prevent the imagination from restoring its original outlines.
4, 44 0)
je fy Ly Jif. Za if, / kg
oy MG , Wf fl! “Wy i / a) | Ws
i ah Mpa f ie
FIG. 62. UPLAND TOPOGRAPHY NEAR BERNER BAY.
A deep long glacier trough traverses the view from dis- tance to foreground. It is occupied in part by a glacier, in part by a filling of glacial waste; and its rock bed is far below sea-level. It is related to the fiords and must be considered in another connection. In the present con- nection it need be thought of only as a trench dividing the upland, and helping, through contrast, to exhibit the upland’s plateau character.
Other illustrations of the plateau dissected by Lynn Canal and its branches are to be seen in figures 75 and
128 ALASKA GLACIERS
77. In each case the point of view is so low that the up- land peaks do not unite in an even sky-line, but other plateau features are brought out.
The correlation of the Cape Spencer peneplain with the Lynn Canal plateaus brings together very different topo- graphic types, but they are not essentially incongruous. The greater height of the inland district has caused it to be occupied by local glaciers, which have scooped out a system of cirques and rounded valleys, leaving the inter- vening crests angular. The cape district is and has been too low to initiate glaciers, but has been overflowed by
Uh, f ht 2 tle Y he > = SS hy AN Rath, UC SSNs : Wein. Poe a eae 5 c? AS Wh mS SS poares el Se LLG ser 2 a cha, La ae aad \ Zs, Lae seine
a ieee
ee ta —— =P 2 ae ae) ee eed mS ¥) ayy Sonny — = pe, ia SS a
FIG. 63. UPLAND TOPOGRAPHY NEAR WALKER BAY, BEHM CANAL.
an ice-sheet originating outside it. It therefore lacks cirques and the sharp crests developed by cirque erosion, but has suffered a somewhat equable reduction of its flat- tish summits.
In turning attention now to figure 63, we leave the region of Lynn Canal and pass three hundred miles south- ward to the Walker Bay region near Behm Canal. The general height of crests is here 4,000 feet. The even sky- line includes a few sharp peaks, suggesting the cirque sculpture of the northern area, but most of the distant summits and all of the nearer are rounded, as by an over-
HIGH PENEPLAIN 129
riding ice-sheet. The deep dissection indicates a subse- quent history different from that at the north, but the evidence of an initial peneplain is at least equally clear. The approximation of the summit heights to uniformity is too close to be accounted for without the hypothesis of an uplifted plain; but the departures from uniformity indicate that little if any of the original plain survives.
The general interpretation of these upland features ap- pears to be as follows: After the folding and squeezing of the metamorphic rocks, there was a long period of erosion, in which broad tracts of the land were worn down nearly to sea-level. Then came uplift, producing a plateau from 3,000 to 6,000 feet high, and erosion has followed. In some places, at least, this plateau sloped gently toward the sea, and its plane may have remained everywhere continuous, diversified only by moderate flexures; but there is also possibility that it was inter- rupted here and there by faults. The period of subsequent erosion has been long enough for the development of local peneplains at a lower level, and in that time the plateau has been greatly modified. Not only has it been dis- sected by the eating out of gorges and valleys, but its back has been worn and fretted, largely by local glaciers, until all the original surface and much of the original form have disappeared. What remains is chiefly a tendency to uniformity of crest height in the ridges and peaks of certain districts.
It is probably true also that vestiges of the high pene- plain are conspicuous only where the rocks are com- paratively durable. Our best examples are along the mainland east of the archipelago, and that region, accord- ing to Dawson, is largely granitic. The dominant rocks of the archipelago are metamorphic, and we saw little from the ship’s deck to suggest that the uplands of the islands have a plateau habit. The mountains next the
130 ALASKA GLACIERS
water do not in general rise very nearly to the plateau plane, and we were frequently able to see that those farther back are higher. Even where the channels between islands are most sharply incised it is probable that they are excavated in the bottoms of broader hollows.
My general conception of the configuration at the date of the lower peneplain—a conception necessarily vague, as well as provisional — is that it included all phases of the topographic cycle, being infantile to adolescent where the rocks are most resistant, adolescent to mature in the greater part of the Alexander Archipelago, and senile where the rocks are weakest. In the granites were nar- row gorges, set far apart, and reduced to low grade only where draining large tracts. Between them were tabular uplands with mild relief, except for occasional unreduced peaks, or monadnocks. In the stronger metamorphics a system of graded waterways divided the upland into mountain ridges, with scattered remnants of the summit plain. The master streams were largely consequent to the seaward slope of the old plain, but were in part diverted to lines of strike; and minor streams were ad- justed to rock structure.
Low Peneplains.—Along the passages and channels we traversed, bold coasts are the rule and forelands of any character the rare exception, but at two localities we saw unmistakable traces of a peneplain between mountain base and the descent to deep water, and in the light of their evidence it seemed proper to give a similar interpre- tation to various features of obscurer character.
Annette and Gravina islands lie next to the mainland in the southern part of the Alexander Archipelago. Out- side them on the west is the great Prince of Wales Island, from which they are separated by a broad channel, 1,500 to 1,700 feet deep. Each island contains a mountain mass bordered on the west by a low foreland, the foreland being
LOW PENEPLAINS ee
related to the mountain as peneplain to monadnock. On Annette Island, where we landed, the foreland is not continuous, being divided by a bay, but its parts, together with several low islands, appear to be remnants of a more extensive plain. The rock is slate and mica schist, and _ that of the adjacent portion of the mountain quartzite. In detail the surface is somewhat uneven, low moutonnée bosses alternating with hollows that hold pools and bogs, but there is a general and gradual ascent from the sea front to the mountain base, where the altitude may be three or four hundred feet. Figure 64 presents one rem-
FIG. 64. PART OF ANNETTE ISLAND.
Showing relation of foreland (peneplain) to mountain, as seen from New Metlakatla.
nant of foreland in profile, as seen from the other, and in- cludes also rocky islets.
As this whole region was deeply buried by Pleistocene ice, the unevenness of the foreland is readily understood as the result of glacial erosion subsequent to the original planation. Probably none of the original surface remains, but the glacial degradation must have been locally quite moderate, or the general plain character would not have survived. The phenomena do not yield a close determi- nation of the pre-glacial relation of sea-level to land, but it could not have differed greatly from the present.
The second locality is Sitka Sound, 175 miles to the northwest, and on the ocean front of the archipelago. Back of Sitka the mountains of Baranof Island rise abruptly to a height of several thousand feet, and they are penetrated by inlets and lake valleys exhibiting a moderate development of fiord characters. But the town
132 ALASKA GLACIERS
itself stands on a foreland carved from the rock, and this foreland slopes gradually under the water of the sound or bay. In detail the foreland is even more rugged than that of Annette Island, and where it passes beneath the water its eminences give rise to a great number of islets, which stud the sound and form the natural breakwater of Sitka Harbor. ‘The relations of mountain, foreland and islands are well shown in plate xvi (lower view) and figure 65, which represent Cape Baranof, a few miles south of Sitka. Here also the in- dicated base- level has ap- proximately the height of modern
== pepe. sea-level.
— —=
; Ve About FIG. 65. OLD PENEPLAIN NEAR SITKA. ° Wrangell Seen from the timber line on Mount Verstovia.
and Wran-
gell Strait, a region on the landward side of the archi- pelago, we saw more extensive tracts which probably pertain to the same base-level. They stand somewhat higher, averaging several hundred feet in altitude; and the parts we saw best have been so modified by glacial erosion that original base-leveling might not have been inferred without the aid of the Annette and Sitka exam- ples. They are illustrated by the upper view in plate XVII.
Near the south end of Lynn Canal, Douglas Island is separated from the mainland by a narrow fiord, the Gas- tineau Channel. Facing the channel, the island is flanked by the ruins of a high rock terrace (fig. 66). A dozen short valleys of the island join the fiord at the level of the terrace, which descends southeastward from an estimated
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EXPLANATION OF PLATE XVII
Upper Figure. — LOWLANDS NEAR WRANGELL
Standing south of the main town the observer looks southwestward across the harbor. The narrow foreland on which the town stands, and the peninsula beyond the harbor, are composed of metamorphic rocks, and are probably remnants of a dissected and greatly worn pene- plain. -: The rounded crests of the mountains beyond suggest that they were overridden. by the Pleistocene ice-sheet. See page 132.
From a photograph made by E. S. Curtis, June 5, 1899. Negative
NO. 195.
Lower FicurE.— FORELAND AND ISLANDS NEAR SITKA
The view looks south and southwest from the hillside back of Sitka. The islands of the harbor, and the foreland beyond, Cape Baranof, are believed to be parts of a peneplain subsequently worn by a glacier. See page 131, and compare figure 65, which gives a bird’s-eye view of the same features.
From a, photograph made by E. S. Curtis, June 16, 1899. Nega- tive No. 236.
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133
LOW PENEPLAINS
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134 ALASKA GLACIERS
period that the chief pre-glacial erosion of the plateau was accomplished. While the granite tables were being dissected and the harder metamorphics worn into varied and rugged mountains, flat valleys and plains were devel- oped from the broader bodies of weak rocks.
A Lower Base-level. —'The degradation of the troughs in which lie the channels, passages and straits among the islands, and the fiords of the mainland, has been carried far below the horizon of the lower peneplains. Close to the Annette Island peneplain Clarence Strait has a depth of 1,675 feet, and 50 miles farther north, where the strait is narrowed by Cleveland Peninsula, a depth of 2,100 feet is recorded. Thirty miles inland from Annette Island Behm Canal is 1,800 feet deep; and 60 miles in- land, toward the head of Portland Canal, is a depth of 1,250 feet. The greatest recorded depth of Chatham Strait, 60 miles from either end and 25 miles inland from the Sitka peneplain, is 2,900 feet; and its northward prolongation, Lynn Canal, has one sounding of 2,475 feet. These fig- ures are selected from charted soundings which indicate great irregularity of bottom configuration; they are maxima, and not averages; but the averages also are im- pressive. Inthe main part of Lynn Canal (55 miles long) the average sounding along the line of greatest depth is 1,300 feet. The similar average for the surveyed part (60 miles) of Chatham Strait is 2,000 feet; for Stevens Passage 1,000 feet, Frederick Sound goo feet, Summer Strait 1,100 feet, Clarence Strait 1,500 feet, Behm Canal 1,400 feet, Portland Canal 1,000 feet. These are all in the region of the Alexander Archipelago. ‘The broad sound east of Queen Charlotte Islands, called Hecate Strait, ranges from 150 to 600 feet, and the narrow passages east of it are somewhat deeper. Queen Charlotte Sound, northeast of Vancouver Island, has a general depth of 600 feet and a maximum of 1,140; the Gulf of Georgia a
LOW BASE-LEVEL 135
rough average of goo feet and a maximum of 1,470; the narrow passage joining the sound and gulf an average of 600 feet, with a greatest depth of 1,000. At the extreme south Puget Sound has an average depth of 500 feet and a maximum of 925.
With the possible exception of Hecate Strait, these water-filled valleys are clearly products of erosion; and it is probable, though not proved, that they are younger than the low peneplains. Whatever the extent to which they were hollowed out by rivers, they were afterward greatly modified by glaciers; and the glaciers are respon- sible for the conspicuous unevenness of their floors. The demonstration of ice work is found in the thorough glaci- ation of all bordering lands, to be presently described, and in the sculpture of rocky islets, which have characteristic moutonnée forms. Much of the unevenness, and espe- cially the deeper basins, must be ascribed to glacial erosion, but a share may also be referred to glacial depo- sition.
Whatever the extent to which the hollows were deep- ened and enlarged by glaciers, it is probable not only that they were initiated by rivers, but that some of the rivers sunk their beds considerably below present tide- level. The most satisfactory evidence on this point was found at the extreme south. In the Puget Sound region, as shown by Willis, the ice movement was southward, a lobe of the ice-sheet ascending the broad valley of western Washington. This lobe made extensive modification of the face of the country, but chiefly by deposition and only secondarily by erosion. The system of troughs it left behind are regarded as preexistent stream valleys, only moderately scoured and straightened by the ice which overran and occupied them.’
1Drift Phenomena of Puget Sound. By Bailey Willis. Bull. Geol. Soc. Amer., vol. rx, pp. 111-162, 1898.
136 ALASKA GLACIERS
This interpretation by Willis seems to me reasonable. The glacial deposits in the southern part of the Puget Sound region are voluminous, and much of their material is of distant origin. This is the place where the ice lobe discharged its load, and it is not probable that in the field of deposition the ice also developed by erosion a system of narrow deep troughs. Regarded as stream valleys, the channels of the sound tell of a pre-glacial base-level at least 500 feet, and probably 1,000 feet or more, below the present sea surface.
A few features seen at the north might be regarded as confirmatory, but their interpretation is subject to con- siderable doubt. They are apparent exceptions to the general rule that at all low levels the sculpture forms of trough walls are glacial.
But while the existence of a pre-glacial low base-level is on the whole probable, its precise relation to present base-level and the period of its duration are altogether conjectural. To bring all parts of the deep channels within reach of stream erosion it would need to be 3,000 feet below present sea-level in the region of the Alexander Archipelago. Under present climatic conditions, such a change would carry a very large area above snow-line, and would so promote the alimentation of glaciers as to flood the whole district with ice and abolish stream ero- sion. Stream erosion, therefore, could not have been carried, by lowering of base-level, to the lowest parts of the channel system without the aid of important climatic variation. Without doubting the possibility of wide range in independent climatic factors, it seems easier to assume that the lowering of base-level was comparatively mod- erate, and that a considerable part of the down-cutting of the channels was accomplished by Pleistocene glaciers.
There is equal doubt as to the duration of the low base-level, or the extent of the erosive work it enabled
LOW BASE-LEVEL 137
the streams to accomplish. The questions whether the broader channels of the archipelago were merely outlined by river gorges or were widely opened, whether the low peneplain was only trenched or was largely replaced by a peneplain at a level now submerged, whether the grading of river beds was restricted to the coastal district or was carried far into the interior, are not answered by any facts in my possession.
To escape the confusion arising from the glacial re- modeling of water-wrought topography, it is natural to turn to the region just outside the glacial district. This region may be assumed to have shared the same oscilla- tions of base-level, so that whatever history may be derived from it can be transferred to at least the neighboring parts of the glacial district. The glaciation of what may be called the inner coast has its southern limit in Puget Sound. As the Olympic Mountains, separating the sound from the outer coast, contained Pleistocene glaciers, the outer coast also may have been modified by ice in that latitude. But farther south the coast was not directly affected by glacial ice. Between the Olympics and the mouth of Columbia River are two shallow bays, partitioned from the ocean by sand spits. The more northerly, Gray Harbor, receives the Chehalis River, a stream of moderate size, but the map gives no indication of a delta. Willapa Bay receives two small streams, Willapa and Nasal rivers, and these also are without deltas. It is evident that the bays are estuaries, or submerged portions of the river valleys, and they indicate a recent change in the relation of sea and land, the sea rising or the land sinking.
Columbia River also ends in an estuary, its banks grad- ually separating, until near the sea they are ten miles apart. The estuary is shoal, and it is a matter of observa- tion that the parts protected from the current are being rapidly filled by the abundant silt of the river. The banks
138 ALASKA GLACIERS
are in part low, but include also hills and bluffs. While this estuary is much larger than those of Chehalis and Willapa rivers, it is small in relation to the Columbia River, which carries a great volume of water, and the val- ley whose submergence it records was of very moderate dimensions. This valley was of course formed while the river ran at a lower level, but the erosive work accom- plished at that level was surprisingly small. As the con- tinental shelf is narrow along this part of the coast, the river may be supposed to have promptly graded its chan- nel to harmony with the depressed base-level, and the conditions would seem to have been favorable for the development of a broad and branching valley like that submerged in Chesapeake Bay. The fact that no such development took place seems to indicate either that the lowering of base-level was small or that the period of low base-level was short. Despite the great volume of the river, the valley developed by the discharge at lower level was quite insignificant in comparison with the fiords and channels of the neighboring glaciated coast.
These features would have an important bearing on the question of low base-level in the district of the inside passages if we could be sure that the history of the Columbia estuary was really pre-Pleistocene; but there is | reason to suspect that the Columbia has somewhat re- cently come into possession of the lower part of its valley. After passing the Cascade Mountains it turns northward in the great structural valley which farther south contains Willamette River and farther north holds Puget Sound. Then at the mouth of the Cowlitz it again turns westward, and traverses a low range of mountains or hills in a some- what narrow passage. Close to the river these mountains have a height of 1,000 feet or more. From the mouth of the Cowlitz northward to Puget Sound the country is comparatively low, and the summits are occupied by
GLACIATION 139
Pleistocene gravels. These features, while not demon- strative without further study, clearly suggest that the Columbia may formerly have followed the structural val- ley northward to and through Puget Sound, reaching the ocean by way of Fuca Strait. The occupation of the strait and sound by the great Pleistocene glacier would have compelled the river to find some different course, and when it had once carved a channel through the coastal hills the filling of its previous channel by glacial gravels would prevent its return to the earlier course.
In view of the possibility that the lower course of the Columbia dates only from the Pleistocene, it is evident that the character of its estuary has no decisive bearing on the problem of pre-Pleistocene base-level.
Summary.— Before the great glaciers of the Pleistocene began their work the district included a varied topography. The larger part was mountainous in the ordinary sense, with crests at various heights and a complicated system of steep-sided ridges, spurs and gorges. There were exten- sive remnants of a high-lifted peneplain, its plateaus mark- ing the areas of most resistant rock, and above these plateaus rose summits of the nature of monadnocks. There were remnants of a low peneplain—a peneplain which is now near sea-level—and these occupied areas of relatively weak rock. There was a system of river valleys or master lines of drainage, narrow where the rocks were most resistant and more open among weak rocks. The bottoms of these valleys were in part below tide-level.
Glaciation
Rounding of Angles.— Turning now to the results of Pleistocene ice erosion, one of the most evident is the rounding of salient features. Where the slopes of moun- tain spurs have an average inclination as steep or steeper than that which permits the resting of talus, the inter-
140 ALASKA GLACIERS
mediate crest line is normally acute and serrate. The association of steep slopes with rounded summits is an abnormal condition requiring special explanation, and in glaciated districts there is a strong presumption that the rounding has resulted from the removal by ice of the salient parts of the spurs. ‘The rounding, therefore, serves to show the extent of the district which has been subjected to glaciation. It also affords a rough measure of the depth to which the erosion has locally extended, for the imagi- nation restores, more or less truthfully, the original sharp- crested form, and thus realizes the difference between that and the rounded form presented to the eye.
In the district under consideration the work of round- ing has been extensive. Below certain levels the crests and profiles of hills, mountains and mountain spurs are devoid of crags and sharp angles and have curved outlines. From this general rule there are no deviations within the range of our observation, except where it is evident that the forms of glacial sculpture have been modified by later work of torrents or breakers. The rounding is more thorough at low levels than at high. Near its upper limit it often amounts only to the removal of pinnacles and the blunting of angles which would otherwise be sharp; farther down it has not infrequently been carried so far that no suggestion remains of the pre-glacial forms. In many places the depth of rock pared away in the mere smoothing of a rough topography must have amounted to several hundred feet.
The upper limit of rounding was estimated to range from 3,000 to 5,000 feet in the region of the inside pas- sage, and these estimates are in substantial agreement with data given by the maps and photographs of the Canadian Boundary Commission. From the latter I esti- mate the height at 4,500 feet near Behm Canal (fig. 63) 4,000 feet near Berner Bay (fig. 62), 5,000 feet above
GLACIATION I4I
Chilkoot Lake (fig. 77), and 3,500 to 4,000 feet near Brady Glacier (fig. 61). In the neighborhood of Sitka it is about 2,000 feet.
In a general way this limit records the extreme height locally attained by the confluent ice of the Pleistocene. As the line often runs among modern névés and glaciers, where glacial erosion has been in progress ever since the maximum ice flood, there is possibility that the later development of cirques has, in places, carved out sharp blades and pinnacles from summits that had been rounded by the earlier flood, but this qualification is not believed to be important. The upward diminution of the paring of salient angles is such as would naturally obtain near the upper limit of ice action.
My observations of the limit of rounding are not so dis- tributed as to give a comprehensive picture of the extent of the maximum ice-sheet, but they agree fully with Dawson’s conclusion that the whole district was oc- cupied. Where now are sounds and channels the ice depth was _ probably
from 3,000 to 6,000 feet, FIG. 67. A FIORD OF THE INSIDE PASSAGE. but many summits were ‘he tops of distant mountains were smoothed
ice-free. Some of the un- and blunted by overriding ice. covered peaks were nunataks, about which ice currents parted to unite again. Others were the culminating points of mountain masses which served as centers of glaciation. : Cirques. — Other features due to ice sculpture are cir- ques. These occur at all altitudes above 1,000 feet, being most abundant in the higher regions. ‘Those above 3,000 to 3,500 feet now contain névés, and it is probable that they have been occupied not only since the last maximum of
142 ALASKA GLACIERS
glaciation, but in interglacial epochs and during a part of pre-glacial time. ‘Therefore, only a part of the erosion they represent can be ascribed to Pleistocene ice. Those at lower levels were made under Pleistocene conditions and belong strictly to that epoch. It is noteworthy that they occur considerably below the upper limit of ice sculpture; on Kupreanof Island and in Glacier Bay they were seen on the flanks of mountains whose summits are well rounded. Though these lower-lying examples are less fully developed than those about the higher summits, they represent a notable amount of ice work, and that ice work was performed during stages of glacier development intermediate in extent between the modern and the maxi- mum.
Fiords and Hanging Valleys. —'The fiords admit of a partial classification as longitudinal, or strike, and trans-
by Ry Pa mya EZ 2) Uy phi} YY intel ne ZL “a9 ZZ sy a) yy i}
es igs Zee
oN 2
FIG. 68. A FIORD OF THE INSIDE PASSAGE. Ice-rounded mountains in the distance.
verse. Where the courses are direct and accord with the general trend of the coast, and especially where two or more fiords or channels are parallel, it is fair to assume that their positions were determined by structural factors. Where the courses make wide angles with the trend of
FIORDS AND HANGING VALLEYS 143
the coast, and are in detail characterized by short turns, it may be assumed that they are independent of strike. In the case of strike fiords, erosion may have been favored by the presence of weak rocks, but the erosion of trans- verse fiords had no such aid. Our best opportunities for direct observation were of fiords that either probably or possibly follow the strike, and the discrimination of aqueous and glacial erosion, or the problem of the amount of glacial excavation, is thus complicated by a factor in- volving much uncertainty.
Discovery Passage and Johnstone Strait, separating
FIG. 69. HANGING VALLEY ON VANCOUVER ISLAND. Photographed from Johnstone Strait. In the distance, an ice-rounded summit.
part of Vancouver Island from various minor islands and the mainland, constitute a well recognized fiord for 70 miles. With little exception, its walls of rock are steep at the water’s edge and for some distance above and be- low. The central depth of water ranges from less than
144 ALASKA GLACIERS
200 to more than 1,000 feet. The immediate walls are 1,000 to 2,000 feet high, curving back to rounded sum- mits. On the mainland side the fiord is joined by many troughs of similar depth and character, and by a few hanging valleys. From Vancouver Island it is joined by many hanging valleys. The sills of the hanging valleys best seen lie from 200 to 500 feet above tide and are evi- dently carved from the rock. Below each sill the con- tours of the main trough are continuous, without any de- flection toward the side valley, and the draining stream has only begun the work of grading its channel. A shallow trench is cut on the edge of the sill, and escaping from this, the water tumbles down the open face of the fiord wall. Other valleys hang so high that from our low point of view we could not look into them. At a moderate estimate the highest seen are 1,000 feet above the water, and as these occur opposite the deeper part of the chan- nel it is probable that the maximum discordance of valley floors is not less than 2,000 feet. All the hanging valleys appeared to be steep-sided glacial troughs, and those we saw best are at least several miles in length, with moun- tains behind them. :
For this complicated system of troughs I have not been able to suggest an origin that does not involve an immense amount of excavation by ice. The hypothesis demanding least of the ice is one which assumes the main fiord to follow a belt of weak rock,in which pre-glacial streams had sunk their beds rapidly, outstripping such small trib- utaries as had strong rocks to contend with. Under such conditions, all pre-glacial valleys, with the possible exception of those in the weak rock, would have been narrow gorges, and the work of the ice in enlarging them to existing dimensions would be at least as great as the preceding work of the streams. While this work was be- ing done by the tributary glaciers, the trunk glacier may
FIORDS AND HANGING VALLEYS T45
readily have carved from the weaker rock all that part of the fiord trough lying below tide-level.
The hanging valleys seen on Vancouver Island were evidently shaped by ice currents originating on the island and directed toward the mainland. During their existence the island contained a center of ice distribution. The general condition of the district at this time has been worked out by Dawson from studies of the strie and other features of ice sculpture, made along the coasts of Vancouver Island, of the neighboring mainland, and of various smaller islands in the intervening sound. The principal flow of ice was from the mountains of the main- land, taking the form either of wide individual streams or of a great confluent sheet; and this flood, banking against Vancouver Island, was divided and deflected. One great division, the ‘ Queen-Charlotte-Sound Glacier,’ moved northwestward to the ocean, spreading over the north end of the island. nee Theother great ‘Wf division, the ‘Strait-of-Geor- gia Glacier,’ moved south- eastward and then turned westward to the Strait of i= == = Fuca Itis ny aie
- 70. H. I ALL probable, also, FIG. 7 ANGING VALLEY ON PRINCESS ROYAL ISLAND,
B. C., SEEN FROM FRAZER REACH. that a branch of
this stream, reinforced by tributaries from the Cascade Range in northern Washington, flowed southward as the Puget Sound Glacier.
- 1 Additional observations on the Superficial Geology of British Columbia and adjacent regions. By George M. Dawson. Quart. Jour. Geol. Soc. London, vol, XXXVI, p. 278, 1881.
= nm)
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146 ALASKA GLACIERS
The thorough rounding of crests on Vancouver Island extends so far above the floors of the observed hanging valleys as to indicate that their glaciers were not features of the stage of maximum glaciation. It is quite possible that the greatest flood from the mainland turned back the feebler streams originating on the island and sent currents, here and there, through mountain passes to the southwest- ern coast.
Along the narrow passages separating Princess Royal and Pitt islands from the mainland, hanging valleys are
| : equally abun- ; dant, and the illustrations of the physio- graphic type are even more striking. The
greater tribu- FIG. 71. HANGING VALLEY, FRAZER REACH. tar y va 1 1 e y S Ice-rounded summits in the distance.
approach the fiords from the mainland and have sills near water-level, some of them lying so low as to contain shallow bays. All of the sills on the side of the islands are above tide, and the valleys back of them are surprisingly broad when considered as the channels of glaciers originating on is- lands only fifteen to twenty miles wide. The change of gerade from the floor of the hanging valley to the side wall of the main valley is so abrupt as to give the impres- sion that the sill is really a parapet, and that the alcove in the fiord wall contains a basin. At one point (fig. 70) we climbed to a sill with the half expectation of discover- ing a lake beyond, but found only the uneven, and in places marshy, floor of an ordinary U-trough. The high- est sills seen are about 1,000 feet above tide.
As Grenville Channel, the passage separating Pitt Is-
FIORDS AND HANGING VALLEYS 147
land from the mainland, is straight, and as it has a parallel on the opposite side of the island, it is confidently classed with the strike valleys. At each end it connects with much wider fiords of the mainland, having the crooked courses of transverse valleys. From these relations I infer that the pre-glacial master drainage was transverse, and that the Grenville valley was not followed from end to end by a pre-glacial stream, but contained two streams, flow- ing in opposite ways from a medial sum- mit. The pas- sage about. Princess Royal Island is not clearly marked as a strike valley, but its narrowness as compared with the trans- verse valleys in which it ends indicates that it origi- nally contained two minor streams, with a summit be- tween. No trace of either summit has survived the glacial remodeling. As in other fiords, the bottoms are irregular, but some of the lowest points lie midway be- tween the ends. In fact, the deepest soundings reported in the two passages (severally 800 and goo feet) are near their middles, and are not exceeded by recorded sound- ings in neighboring waters. When it is considered that these fiords, being parallel to the coast, run athwart the general movement of the ice from land to sea, the fact that their depth is comparable with that of troughs lying in the direction of general movement is certainly remark- able. It probably depends in part on the presence of a belt of easily eroded rock, but after all allowance for such favorable condition, one is impressed by the ability of ice
——“- y
FIG. 72. HANGING VALLEY, FRAZER REACH.
148 ALASKA GLACIERS
to cut down its bed far below the profile which limits the action of running water.
The essence of the explanation is contained in Gan- nett’s theorem that the glacier- fon Pee rag made valley is
Soe! teem AY ,{/ homologous, not < ; ‘aS Ae Vas with the river- yy See g'| made valley, but a oi gi) with the chan- YAY, nel made by the eet river. The bot- " tom of a river channel is not evenly graded like its flood plain, but it abounds in hol- lows and hills, and the bottom ofa glacier chan- nel has irregu- larities that are similar but on a larger scale.
A phase of the Pleistocene con- dition of these passages is illus- trated along the The inlet occupies a glacial trough entering Grenville Channel base of the Fair-
from the east. weather Range from Icy Cape to Cape Fairweather. A foothill ridge, 35 miles long, is separated from the range by a nearly con- tinuous groove. <A dozen alpine glaciers descend to the
‘ Lr rave - - : - < ot oat
FIG. 73. NORTH WALL OF LOWE INLET.
149
FIORDS AND HANGING VALLEYS
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150 ALASKA GLACIERS
groove and are there gathered into trunks which follow the groove lengthwise till escape is found through some break in the ridge. The surfaces of trunks and tributaries are mutually adjusted where they join, but it is easy to imagine that the progressive erosion of their beds is: re- lated to the volumes of the glaciers, and that the greater ice streams have the deeper channels. It is interesting to note in this connection that the bottom of this trough is below present tide-level— at least in part—in spite of the fact that there has here been a post-Pleistocene eleva- tion of land. Figure 74 shows a portion of the trough where it is occupied partly by glaciers and partly by an arm of the sea. The observer stands on the foothill ridge. Lituya Bay has the form of a letter T, the cross-bar ap- pearing inthe view, and the shaft running through the foot- hills at the right. ‘The large glaciers in the distance and foreground reach the longitudinal groove from deep mountain gorges. A small glacier, whose end barely touches the water, cascades over a sill that may be 800 feet above tide. A hanging glacier at 2,000 feet or more sends a tongue down a shallow groove in the steep wall of the fiord. And, at the extreme left, a pocket glacier occupies a hanging valley at an altitude of 3,000 feet.
The depth of the glacial excavation in the passages by Pitt and Princess Royal islands was probably about as great as in the passage by Vancouver Island. ‘The scale of the topography is not far different, the evidence from hanging valleys is equally cogent, and the case is strength- ened by the presumption in favor of pre-glacial summit levels. Even with a low base-level it is not at all prob- able that pre-Pleistocene streams carried the erosion of any considerable part of these troughs below present sea- level, and the water partings within them may well have been a thousand feet higher.
One of the more important passages of the Alexander
STRIKE FIORDS I51
Archipelago is so direct in its course that a straight line 190 miles in length could be laid out upon it without touching either shore. It heads in the mainland at the extreme north and, trending a little east of south, termi- nates in the Pacific coast. The southern three-fifths, which bears the name Chatham Strait, has an average width of about seven miles; the northern two-fifths, known as - Lynn Canal, averages five miles. Our direct observation -was restricted to the northern part.
This straightest of all the passages is also deepest. No soundings have yet been charted for the southern third, but those of the northern part indicate that a continuous channel can be traced with 7oo feet as its minimum depth, and the maximum depth, as already mentioned, is 2,900 feet. The bounding mountains, so far as we saw them, are 4,000 to 5,000 feet high, and the full depth of the trough is in the neighborhood of 6,000 feet. At its head the trough divides into four parts, which penetrate the upland, first as fiords or inlets and then as river val- leys. These parts diverge from their point of junction like the ribs of a fan, their directions ranging from north to northwest; and their courses are remarkably straight, especially in the lower parts.
The unusual straightness of this great trough naturally suggests that its course was determined by some struc- tural feature, such as a fault or the outcrop of an easily eroded rock. Its breadth is in better accord with the second of these tentative explanations; but the matter is not free from doubt. If the trough is a strike valley, we should naturally expect to find parallel valleys associated with it, but the number of such is limited. A short parallel trough lies fifteen miles west of Lynn Canal and contains Excursion Inlet. East of Chatham Strait are Seymour Canal and Stevens Passage, which are approximately parallel. But a number of other features
ALASKA GLACIERS
152
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STRIKE FIORDS 153
in close association exhibit a systematic northwest trend; these are Icy Strait, Freshwater Bay, the main part of Tenakee Inlet, and Peril Strait with its prolongation in Hoonah Sound. The divergence of the branching fiords at the head of Lynn Canal is also perplexing; for, while each of these is so straight as to suggest an origin con- nected with strike, they are not parallel, but diverge fan- wise from a common point.
The walls of Lynn Canal are well-defined features. At the water’s edge and for some distance above, their con- tours aresimple. There are few bays and no jutting prom- ontories. The slope of the walls is not so steep as in some fiords; it rarely exceeds 45°, and in places is as low as 30°. Near the head of the canal the walls are well defined up to an altitude of about 2,000 feet, the height increasing toward the north and decreasing toward the south. Higher up, the mountains exhibit a varied topog- raphy: There are U-shaped troughs end- ing as hang- ing valleys at many differ- ent heights; there are V- shaped gorges modified at bottom by
glaciers and The sill of the hanging valley is 3,500 feet above sea-level. For separated by more than 1,000 feet below the glacier the fiord wall is kept bare by
narrow ten ti- falling fragments of ice.
form spurs. These troughs, gorges and spurs approach the canal wall at all angles and there end. Some- times they end abruptly, sometimes with a certain amount of prolongation down the steep wall; but this prolon-
FIG. "6. HANGING GLACIER, TAIYA INLET.
154 ALASKA GLACIERS
gation never extends to the water, and usually does not affect the slope within one or two thousand feet of the water. Their relation is such as might arise if the topog- raphy of the upland had formerly extended farther in the direction of the main trough and afterward been truncated by the development of the trough.
The branch troughs which unite to form the canal have similar walls, which rise higher before meeting the varied topography of the upland. They are also narrower, and at least two of them contract in their upper parts so
~~ Lf, ALE VI oy tf): ¥ A
\ ¢ Mi fe
Wz. WY PD Yl LLEEZ Le ZZ Zi y —Yy yy,
oy 4
FIG. 77. NORTHEAST WALL OF THE CHILKOOT TROUGH.
Below is Chilkoot Lake, and beyond are Chilkoot Inlet and Lynn Canal. The lower part’ of the mountain was shaped bya great Pleistocene glacier, the upper by small tributaries, which survive. The summits are ice-rounded nearly or quite to 5,000 feet. The floors of hang- ing valleys are at 3,500 to 4,000 feet.
that the cross-profile is more nearlya V thana U. Skag- way Canyon, a tributary to the Taiya trough, is narrow at bottom, except where occupied by alluvium. Glaciation has smoothed its walls on a grand scale, and has degraded its bottom enough to render the floor of a tributary dis- cordant to the extent of 50 or 100 feet, but the type of cross-section acquired from pre-glacial stream erosion has not been destroyed. Photographs show that the upper
STRIKE FIORDS 155
part of Taiya Valley has a similar character, and it seems to me probable that these gorges have been only moderately deepened by glaciers. The pre-glacial stream grades which they suggest would pass below present tide- level before reaching the head of Lynn Canal, and would be adjusted to a quite low base-level at the south end of Chatham Strait.
The bottom of the main trough is characterized by much
WH YVAVVVWJJJC=/-
FIG. 78. PROFILE FROM TAIYA PASS SOUTHWARD.
The profile follows the lowest line through Taiya Valley, Taiya Inlet, Lynn Canal and part of Chatham Strait. Whole distance 165 miles. Vertical scale about ten times the hori- zontal. Base line 3,000 feet below sea-level. The approximate height of mountains east of the trough is indicated.
irregularity. The line of deepest water is sinuous and often wanders far from the middle, and along this line the depth varies irregularly (fig. 78). The soundings are
Preis Pp VPr=: Y/7 ys
CTX.
OEP VME EEL.
FIG. 79. CROSS-PROFILES ABOUT HEAD OF LYNN CANAL.
Based on contour map by Canadian Boundary Commission and soundings by U. S. Coast Survey. The positions are indicated by corresponding letters in figure 78. Profile A crosses Chilkoot Lake (fig. 75), Ferebee Inlet and Taiya Inlet. Profile B crosses Chilkat Inlet, near Davidson Glacier, and Lynn Canal. Profile C crosses Lynn Canal below Sullivan Island. S. L., sea-level. Base line 3,000 feet below sea-level. Vertical scale same as horizontal.
too far apart to give expression to details of configuration, and we do not know to what extent the irregularities may
156 ALASKA GLACIERS
be ascribed to unequal deposition of drift, but there is reason to believe that much of the inequality pertains to the rock floor and is to be ascribed to glacial erosion as conditioned by varying resistance of the terrane. A number of islands and one long peninsula are so placed that they may properly be regarded as portions of the trough bottom which rise too high to be covered by the sea. They are of rock, are thoroughly glaciated, and their axes, as well as all flutings and other lines of sculpture, are parallel to the fiord walls. Ice erosion has gone so far as to destroy all semblance to the forms characteristic of aqueous sculpture. Several islands and the southern part of the peninsula are shown in figure 3, and the view in figure 75 was made from the summit of the penin- sula, 1,750 feet above sea-level.
From these various facts, as well as from general im- pressions to which it is not easy to give definite expres- sion, I would draw the following tentative inferences: The V-gorges at the heads of branches of Lynn Canal and in the uplands bordering the canal, were made chiefly by pre-glacial streams, and they have been but moderately deepened by glaciers. There was a pre-glacial, com- paratively narrow, valley through Lynn Canal, the floor of the valley being below present sea-level and related to a low base-level. Lateral V-gorges were tributary to this and were largely adjusted to it in grade. The Pleis- tocene glacier broadened the river valley, truncated the side spurs and the tributary gorges, and at the same time materially deepened the valley for the whole breadth of the trough. The glacial degradation is conceived as averaging hundreds of feet and possibly more than one thousand.
The lateral valleys so situated as to carry glaciers under other than Pleistocene conditions, are thoroughly shaped in characteristic U forms, and they now contain glaciers.
STRIKE FIORDS 157
There are also valleys which are now free, or nearly free, from ice, and which were filled with ice only in the presence of the great glacier, and these have less charac- teristic glacial forms. It would seem that the presence of the great glacier in Lynn Canal gave them so high a base-level that their ice streams were sluggish and had little power of erosion.
The valley of Davidson Glacier deserves special men- tion as an illustration of the broad contrast which may exist between the systems of currents associated with different stages of glaciation in the same district. The névés supplying the glacier are not in sight from Lynn Canal, but lie back of the first line of summits, and the ice river flows eastward through a lateral or transverse valley, entering the great fiord approximately at right angles. During the great ice flood the general direction of move- ment was toward the south, and Davidson Glacier did not exist; its valley was not only filled with ice but over- ridden. It results that the upland bordering the Davidson trough in the vicinity of the Lynn trough, is planed and fluted with lines trending southward, while the Davidson trough, being shaped wholly by the Davidson Glacier dur- ing epochs of moderate ice supply, has an entirely inde- pendent sculpture, the lines of which are transverse to those of the overlooking upland. The Davidson trough is a fine example of its type. So far as visible from the sea, it is of uniform width; its parallel walls sweep ina simple curve of large radius and are steep. Although the topography just above and back of them is varied, they themselves have neither salient nor reentrant angles. The glacier has evidently adjusted its channel quite com- pletely to the conditions of its flow, and has at the same time sunk itself deeply into the mountain it traverses (see fig. 2).
The transverse troughs of the mainland we did not
158 | ALASKA GLACIERS
visit; they are known to me only through photographs, the contour maps of the Canadian Boundary Commission, and the soundings of the United States Coast Survey. As already mentioned, they are judged to be transverse to the strike, because they make wide angles with the general trend of the coast and because they are charac- terized by manyshort turns (fig. 80). Be- ing independent of strike, their courses are also independent of variations in rock texture, and this character makes them specially avail- able for the study of glacial erosion. “Sie, | ‘Theirwalls are steep; -—WIE | photographs give the f, | impression that they are decidedly steeper than those of Lynn Canal’ and 18 branches, but this
FIG. 80. MOUTH OF SPEEL RIVER. impression is pos-
The river is rapidly filling its deep trough withalluvium. «j e to th e ten d- Glacial rounding extends above the base of clouds, which sibly du
cut off the view at about 3,000 feet. ency of photo graph- ers to select localities exhibiting bold scenery. The walls stand well apart, after the habit of glacial troughs, and exhibit notable parallelism (fig. 62). Hanging valleys abound, ranging in height up to 3,000 feet or more and being more numerous at the greater altitudes. Some, like the Stikine and Whiting, are occupied by rivers; others, like the Taku, Speel, Unuk and Skeena, contain rivers in their upper parts and admit the sea below; others, like Tracy
TRANSVERSE FIORDS 159
Arm, Behm Canal and Portland Canal, have the character of fiords through their whole extent. Where rivers flow through them, the whole width from wall to wall is occupied by alluvium, and a lace-work of channels indi- cates rapid deposition. The open water has the depth, and the irregularity of depth, characteristic of fiords. In Tracy Arm, which has a breadth of one mile and a length of twenty, the soundings range from 850 to 1,150 feet. ~The main part of Behm Canal, with a width of two to three miles, has a depth ranging from 1,100 to 1,850 feet. In Portland Canal, which for eighty miles has an average width of two miles, the range of soundings is from 300 to 2,100 feet, and a depth of 1,200 feet occurs near the head. It is scarcely to be doubted that all these long troughs were initiated by pre-glacial rivers; but the rivers could not have opened their valleys to the present width with- out giving time for the breaking down of the walls. If the river valleys were deep, they were also narrow, and their widening was the work of the Pleistocene glaciers. In the work of widening, the more obstructive projections were removed and the contours of the walls were simpli- fied. The amount of erosion necessary to convert the assumed V-gorges into the observed U-troughs is large, and the ice streams by which it was done could not have failed to wear down the floors of their channels at the same time. While it is quite possible that the down- stream parts of the river gorges had been sunk below present sea-level, the greater part of the excavation below sea-level was probably performed by the glaciers. Inequality of Glacial Erosion.— The great work which it has seemed reasonable to ascribe to ice in the deepening and widening of fiords and other troughs stands in striking contrast to the feebleness of ice erosion in other places, which permitted, for example, the preserva- tion of the low peneplains of Annette Island and the
160 ALASKA GLACIERS
vicinity of Sitka. In the one case the depth of the ero- sion is measured by hundreds of feet, in the other by tens. To a certain extent inequalities of erosion were determined by inequalities of resistance, but as the rock of the low peneplain is not of notably resistant character, and the rock traversed by the transverse troughs is in part of highly resistant character, it is evident that this is not the dominant factor. To an important extent also differences of erosion were determined by differences in the depth and consequent pressure of the flowing ice. But I conceive that the most important of the variable factors was the velocity of the ice currents. At the height of the Pleistocene flood the snow-fields were on high pla- teaus and mountain masses, from which the ice crept in broad sluggish streams to the preexisting channels of drainage. In these channels it assumed the character of rivers, and the lines of pre-glacial water drainage became, in the main, the lines of Pleistocene glacial drainage. Along the deeper waterways the ice could flow more rapidly because its depth was greater, and its ability to erode was correspondingly increased. ‘Thus it was that the old river gorges, being adopted as lines of flow by the ice, were widened, straightened and deepened, while the adjacent uplands received comparatively little modifi- cation. The remnants of low peneplain were preserved, despite the softness of their rocks, because they lay out- side the lines of flow of the strong currents. ‘The remark- able deepening of the fiords of the mainland is probably connected in part also with the fact that they were longer occupied by glaciers than were the channels of the archi- pelago. Many of them still have glaciers at their heads; others are flanked by glaciers which would descend and fill them should the climate swing but slightly toward the Pleistocene condition.
The more thorough rounding of salient angles at low
GLACIAL DEPOSITS 161
levels than at high is probably due to the concurrence of several causes rather than to a single one. First may be mentioned the difference in pressure. The rate of abra- sion, and of other forms of erosion, is probably enhanced by pressure, and during the height of the glacial flood all low-lying surfaces were subjected to greater pressure than those at higher levels. A second cause is connected with duration. The coming on and the passing of each Pleisto- cene epoch of glaciation was probably gradual, and there were doubtless glacial epochs of less intensity than the maximum. ‘Thus the crests of low hills were subjected to glacial wear for longer periods than those of high spurs, and the difference may have been very great. Some al- lowance may also be made for subsequent modification at high levels. Ever since the last great ice flood began to wane, the valleys-between high spurs have been occupied by small glaciers, and these have tended, by the develop- ment of their valleys, to reduce the width of the separat- ing ridges. Thus, while the rounding at low levels was still in progress, a work had been begun which tended to reduce the effect of the rounding at high levels.
Glactal Deposits. — In the narrower parts of the inside passages we saw no accumulation of glacial drift. It is possible that drift masses were concealed here and there by the dense forest, but usually the spaces between cliffs and other visible outcroppings of rock were not large. It is probable that drift masses are concealed by the water, _ and have share in the production of the irregularity of the bottom; and a few bars and dams which are known to interrupt the continuity of other fiords are presumably morainic. As it is natural that the routes of travel should avoid such obstructions, it would be rash to infer the ab- sence of local moraines from our failure to observe them. The only important bodies of Pleistocene drift which we saw are on the shores of the Gulf of Georgia, where
162 ALASKA GLACIERS
several extensive banks of waterlaid material constitute terraces, both on the mainland and on the shore of Van- couver Island. These banks are flat-topped, and esti- mated to rise from 100 to 200 feet above the water. One of them was seen to overlap hills with distinctly glacial sculpture, and as they are from 50 to too miles within the limit of the glaciated district they must have been accumulated after the last ice maximum.
The glacial deposits we encountered are of trivial mag- nitude collectively, in comparison with the glacial erosion of which we saw evidence, and it was therefore inferred that the principal regions of glacial deposition lay outside the field of our observation. This inference agrees with the conclusion of Dawson that the ice-sheet embraced the entire Alexander Archipelago, together with all other is- lands of the coast except the Queen Charlotte, and that its outer margin was beyond the present line of coasts.
Associated Sea-Levels.— The question of the relations of sea and land at the time of the great Pleistocene glacia- tion is of much interest, and some considerations bearing on the question will be mentioned, although the evidence at present available is either indirect or negative. As gla- ciers are chiefly phenomena of the land, and as glacial erosion in this district has been carried far below the present sea-level, it is natural to assume that the sea- level associated with that erosion was much lower. A little consideration, however, will show that such a con- . clusion does not necessarily follow. ‘The deepest known hollow ascribable to ice work is in Chatham Strait, and lies 2,900 feet below sea-level. At that point the total depth of the great glacier was probably 6,000 feet. It is commonly assumed that where a glacier enters a sea not deep enough to float it, a part of the ice, equal in weight to the displaced water, is upheld by the water, and the pres- sure of the glacier on its bed is correspondingly dimin-
PLEISTOCENE SEA-LEVEL 163
ished. While I do not regard this assumption as valid, I entertain it for the moment because it gives a minimum estimate of the pressure of the Chatham Strait glacier. If the then sea plane had the same height as the present, the pressure of the glacier would be modified, by assump- tion, by the sustaining power of 2,900 feet of sea water. This sustaining power is equivalent to about 3,300 feet of the total ice thickness, leaving 2,700 feet of ice to press upon the bottom of the strait; and such a pressure would manifestly be ample for the work of erosion. So far as our numerical data go, this locality affords an extreme case; and as the hypothesis of glacial erosion below present sea-level is not barred for this locality, it is prob- ably not barred for the whole district.
Another consideration is connected with the. reaction of the ocean on the front of the glacier. My own obser- vations, though comparatively limited, are so accordant with Dawson’s generalization that I accept with confi- dence his conclusion that the Pleistocene ice front lay outside the present coast line throughout practically the whole district. If the ocean had then its present level, it washed the ice front for hundreds of miles. The power of the ocean to waste a glacier by melting is ordinarily greater than the power of atmospheric agents, and along the present coast of Alaska is much greater. As the fac- tors are complex, it would be difficult to give an analytic demonstration of this proposition, but it is easy to illus- trate by anexample. The great confluent glacier which filled Glacier Bay in the eighteenth century had a general depth of 1,000 to 2,000 feet along the axis of the bay, and rested with less depth on adjacent tracts of land. All through the nineteenth century it was depleted, its wast- ing being brought about partly by the sea and partly by atmospheric agencies. The sea not only melted back the
1See discussion in chapter 111.
164. ALASKA GLACIERS
front for 35 miles, but disposed of a continuous accession of ice from the Muir, Grand Pacific, and other glaciers. Of that portion of the confluent glacier which lay upon the land, a part slid into the sea and was there melted, but another part, which happened to rest on comparatively flat surfaces, remained on the land and has been subjected to only atmospheric agencies of waste. These agencies have not yet completed its destruction, so that extensive patches of stagnant ice, receiving no accessions from névés, remain to testify to the comparative feebleness of the atmospheric attack. I think there can be no exag- geration in the estimate that the melting by the sea has exceeded by ten times the melting from direct insolation and the contact of warm air and warm rain. It is further to be noted that this work of the sea was performed in a land-locked bay, where water cooled by the ice tends to accumulate and is but slowly exchanged for the warmer water of the open ocean. On the outer coast, where the supply of warm water would be constantly renewed by currents, the melting power would be still greater.’
The warmth of the Pacific Ocean in this region depends chiefly on the great circling current of the North Pacific, a part of the planetary system of oceanic circulation which might be modified but would not be stopped by any causes ‘we may suppose to have existed in Pleistocene time. All through the Pleistocene the melting power of the ocean along this coast must have been great, and it is not prob- able that glaciers could so far have withstood it as to ad- vance in deep water. The features of another part of the Alaska coast, to be presently described, render it probable that the glaciers were checked by the oceanic melting somewhere in the belt of shallow water, and were com-
1 Muir Inlet near the glacier is 7,000 feet broad and 500 feet deep. Here Reid found a general temperature, at all depths, of 38° F. The oceanic temperature in the Gulf of Alaska is 58° F. The water of the inlet is 6 degrees warmer than melting ice, that of the neighboring ocean 26 degrees.
PLEISTOCENE SEA-LEVEL 165
pelled there to yield up their load of rock waste. We know, from the extent of Pleistocene erosion in this dis- trict, that the burden of rock waste was large, and wher- ever the moraines were built they made an important de- posit. Ifthe Pleistocene base-level had been the same as the present I should expect to find that deposit as a con- tinuous bar, or string of linear islands, along.the outer coast of the Alexander Archipelago and at various points farther south, but no such features have been described, and the coast seems to have an entirely different character. This consideration, though connected at present with only negative evidence, distinctly favors the theory that the sea- level associated with the greatest Pleistocene ice floods was considerably below the modern sea surface.
There is some evidence, on the other hand, of a com- paratively high sea plane after the glacial maximum. Dawson describes an extensive marine deposit, reaching a height of 200 feet, on the east side of Graham Island, the most northerly of the Queen Charlotte group, and infers from its relations that it was contemporaneous with a development of local glaciers. At Nanaimo, on the inner coast of Vancouver Island, he found shell-bearing marine clays, resting on glaciated rocks, at a height of 70 feet above the sea”. In Gastineau Channel is a narrow shore terrace at a height of 200 feet, and in an associated clay Dall found marine shells. At two, at least, of the localities the shells are of species indicating cold water, and each locality is on the border of a sound or channel which would be filled with icebergs by a moderate devel- opment of glaciers. Ifthe phenomena all belong to the same chapter of Pleistocene history, they record an episode similar to that of the Champlain clays of the At- lantic seaboard.
1 Quart. Jour. Geol. Soc. London, vol. xxxvu, p. 281, 1881. 2 Quart. Jour. Geol. Soc. London, vol. xxxvul, p. 279, 1881.
166 ALASKA GLACIERS
The terrace about Gastineau Channel is rather con- spicuous at Douglas, where the forest has been removed, and was detected at several points where the forest still stands, but I searched in vain for its continuation about the shores of Lynn Canal and Cross Sound.
HIGH MOUNTAIN DISTRICT
Between Cross Sound and Prince William Sound are > high mountains visible from the sea. They are much loftier than those of the Inland Passage district, and probably comprise a number of distinguishable ranges, though their system is not yet known. A mass cul- minating in Mount St. Elias (18,100 feet), west of Yak- utat Bay, has been called the St. Elias Alps, and this name is sometimes made to include the whole chain. A more easterly portion, culminating in Mount Fairweather (15,000 feet), is sometimes distinguished as the Fair- weather Range. Opposite these mountains the coast line is comparatively simple, being interrupted by fiords at a few points only and having no important islands. From Icy Cape westward the mountain base is bordered by a low foreland, narrow at first, but broadening to ten miles at Alsek River and fifteen miles at Yakutat Bay and beyond.
Many alpine glaciers now creep down the face of the range and unite in plateau masses on the foreland, a few of them spreading to the sea. The foreland bears also a system of ridges, of peculiar type, which are be- lieved to be morainic and of Pleistocene age. Mention has already been made of one of these in describing the La Perouse Glacier. The ridge against which that glacier crowds, at the point of our visit, runs parallel to the coast for about seven miles and has an actual height of 1,000 feet, as indicated on the map of the Canadian Boundary Commission. It is nearly straight, is steeper toward the
HIGH MOUNTAIN DISTRICT 167
land than toward the sea, and is contoured on the sea- ward side by a terrace, which probably lies 200 to 300 feet above tide. At the single point of examination this terrace contains marine beds overlain by glacial gravel, and the ridge back of it appears to consist of unsorted drift. ‘The clays, where seen in section, are in part level -and in part disturbed (page 41). The completion of the moraine ridge was subsequent to the deposition of the clays. The undisturbed clays imply, by their posi- tion, a higher stage of the ocean, and the overlying gravels are more readily explained by assuming that the sea-level was still high at the time of their deposition. It seems to me probable that the moraine ridge was depos- ited when the sea stood several hundred feet higher than now against the land.
Toward the southeast the ridge ends against the side of the La Perouse Glacier, and the relations indicate that the glacier is wearing it away. At one time it probably extended considerably farther in that direction, but was so low as to be overridden by the modern glacier and thus subjected to erosion by it.
Lituya Bay, a few miles up the coast toward the north- west, penetrates the land for seven miles, dividing not only the foreland but a low outer range of mountains. Within the mountains its trough has fiord characters, and from the walls of the mountain gateway run two morainic ridges, parallel at first, but curving toward each other and de- scending so as to unite under water at the entrance to the bay. These were seen only from the ship’s deck, but their character is unmistakable. They are steeper within than without, and their inner contours continue those of the passage through the mountain ridge. They extend some- what beyond the general line of the foreland, making a pair of capes which embrace the outer part of the bay. Close to the mountains they have an extreme height of
168 ALASKA GLACIERS
1,000 feet above the sea, as indicated by the contours of the Canadian Boundary Commission’s map.
Between Lituya Bay and the mouth of Alsek River are several other morainic ridges, more or less crescentic in form, and so related to modern glaciers as to indicate that they were formed by them at some earlier epoch, when the ice streams were greater than now. In some cases the modern ice seems to extend to the base of the mo- rainic rampart, and in one instance ice projects through a gap in the rampart; but the height of the old moraines forbids the idea that they were adjusted to glacial condi- tions closely resembling the present. From a distant view some were judged to be as high as 1,500 feet, and the modern glaciers seemed merely to touch their bases, instead of pressing against their inner faces. Asso- ciated with them, and extending along the coast beyond them, are a system of terraces, the highest of which was estimated to be 500 feet above tide; and these suggest that the sea surface stood comparatively high when the moraines were built.
The fact that the old moraines rise far above the modern glaciers but yet inclose areas only a little larger than the modern ice is able to occupy, is notable, and doubtless has an important significance if rightly interpreted. The ex- planation which occurred to me is, that the extent of the old glaciers was restricted by contact with sea water. As already pointed out, a warm ocean, like the Pacific in the Gulf of Alaska, is a most efficient agent for the wasting of glaciers. The high specific heat of water, the freedom of the circulation by which warm water is brought to re- place the water which has parted with its heat, and the great depth of the body of warm water on which this cir- culation can draw, all contribute to this efficiency. It seems to me entirely possible that if the greater glaciers descending from Fairweather Range in earlier times en-
HIGH MOUNTAIN DISTRICT 169
countered the sea soon after reaching the basal plain, they may have been wasted so rapidly along the line of contact as to determine there a principal line of morainic accumulation, and the ramparts of the coast may constitute the record of a successful resistance by the sea to glacial invasion.
If this explanation is correct, the Pleistocene submer- gence of the coast probably extended considerably above the zone of terraces. The oceanic resistance determining the deposition of drift would not be effective after the moraine ridge had been built so high as to become a partition between ice and water, and the theoretic posi- tion of the old sea plane is therefore along or above the highest crests of the moraine.
The hypothetic conditions are similar to those at the foot of Davidson Glacier. If that glacier should shrink, and the sea-level should be lowered in Lynn Canal, the Davidson moraine, if composed wholly of rock débris, would survive as a crescentic rampart with a flat top; and if the ramparts of the Fairweather region are strictly homologous they should have broad and level crests. If, however, the Davidson moraine is not wholly built of rock débris, but consists rather of an apron of débris resting against a concealed ice slope, the resulting ram- part, when ice and water are withdrawn, would have an acute crest, with uneven sky-line; but the crest, instead of representing the plane of the present water-level, would stand somewhat below it. In viewing the old moraines of the Fairweather coast I recognized a few local flat | summits, but the general character of the crest line is acute and its height is not uniform. If, therefore, the re- lation of the old glaciers to the sea was like the present relation of the Davidson Glacier, the sea then stood much higher against the land than now — or else the land then stood lower.
170 ALASKA GLACIERS
Whether these old ramparts represent the limit of Pleistocene ice at the time of maximum glaciation is a question as to which there may be doubt, but I incline to the view that the affirmative answer is the true one. So far as I could judge from distant views, the rounding of rock ridges and crests, characteristic of flooding by ice, extends but a moderate distance above the surfaces of modern glaciers on this part of the coast, and indicates glaciers of about the same magnitude as are indicated by the rampart moraines.
On the northwest side of Dry Bay, which receives Alsek River, a single fragment of a high rampart was seen, and in association with it a terrace; but thence to Yakutat Bay the broad foreland is low, its flatness being relieved only by ridges of moderate height. About Yak- utat Village and Ocean Cape, at the mouth of Yakutat Bay, some of these ridges were seen to be morainic, and it is supposed that the whole foreland is constituted of glacial waste, chiefly of waterlaid gravel. If high ram- parts were formed along this portion of the coast they were afterward destroyed and the material carried sea- ward by later advances of the ice.
On the mountains near the head of Yakutat Bay are fragmentary terraces at various heights ranging up to 1,200 or 1,500 feet, but as they face the bay rather than the ocean, it is entirely possible that they are of glacial rather than marine origin. Hanging valleys occur on the eastern wall of Yakutat Bay and on the walls of Russell and Nunatak fiords. One of these, near Nunatak Fiord, is now occupied by a glacier which cascades for 1,000 feet down the steep wall of the fiord. The sills of these valleys range from tide-level to a height of 1,500 feet or more, and they tell of great erosion by the trunk glaciers. The associated rounding of topographic angles is carried higher above surfaces of modern glaciers than in the
HIGH MOUNTAIN DISTRICT I7I
vicinity of Mount Fairweather, and this character seems naturally related to the gentler declivity of the mountain front. The enhanced alimentation of Pleistocene glaciers would tend everywhere to increase their thickness and their rate of flow, but it is easy to understand that the greater resistance to flow encountered on a gentle slope would cause
the thicken- WM CLUE
: Gif SN VG ALN (6g
ing there to | (S85 LL vs Gi Os SD g FEM 4 ig a
be more nota- ble than ona steep slope. So far as may be judged by the gradi- ents of the neighboring Malaspina
. FIG. 81. HANGING VALLEY ON THE SOUTH SIDE OF Glacier, the NUNATAK FIORD.
ice flood as- sociated with the hanging valleys and rounded crests of the Yakutat region should have extended farther seaward than the line of the present coast, and it is probable that the outer morainic deposit is not visible. ‘The submerged moraine ridges within the bay and across its mouth (page 49) pertain to quite moderate expansions of the Malaspina Glacier. |
The inference that the sea-level associated with the moraine ramparts coincided with their highest summits may be interpreted in terms of land change or sea change. The local phenomena would be explained by assuming that the land has risen about 1,500 feet since the building of the moraines, or by assuming that the sea has subsided that amount, and it is, of course, possible that there have been changes of both land and sea, and that the discord-
172 ALASKA GLACIERS
ance of levels represents their sum or difference. While the question thus raised is not susceptible at present of a complete answer, it is nevertheless possible to make some progress in that direction.
In studying the Alexander Archipelago, which adjoins the Fairweather coast on the southeast, no evidence was found of a high sea-level in association with the greatest Pleistocene glaciers; but it seemed probable, on the con- trary, that the mid-Pleistocene sea-level was considerably lower than the modern sea-level. Beyond the St. Elias Mountains, in the opposite direction, lies the district of Prince William Sound, and the Pleistocene history of that region appears to resemble closely that of the Alexander Archipelago. The Pleistocene history of the Fairweather- St. Elias coast thus appears to be exceptional and to be con- trasted with the histories of neighboring coasts on both sides. ‘This contrast is associated with a contrast in gen- eral geologic history, as revealed in the physiography. The district of the Alexander Archipelago is genetically a plateau, from which mountains and valleys have been developed by erosion. The district about Prince William Sound has been found by Schrader and Spencer? to have the same character and history. In each case a region of complex structure was reduced to a condition of low peneplain by long-continued erosion and then uplifted bodily though somewhat unequally. The original altitude of one plateau ranged from 3,000 to 7,000 feet, that of the other averaged 6,000 feet. The intervening tract has been lifted to a much greater height, so that its culminat- ing peaks have altitudes of 15,000 to 19,000 feet, and it is probable that crustal deformation here produced mountain ranges directly, instead of creating a plateau from which they were developed by erosion.
1 Geology and Mineral Resources of a portion of the Copper River district, Alaska. U.S. Geol. Survey, pp. 62-76, 1901.
PRINCE WILLIAM SOUND 173
Two facts indicate that these mountains are geologically young. The first is paleontologic. Russell found, in one of the lower spurs of Mount St. Elias, a fossil marine fauna composed wholly of forms which still inhabit the coastal waters of Alaska.’ These show that the last great elevation of the mountain range is recent, as measured in terms of biologic evolution. The other evidence of youth is found in the great height of the mountains. As pointed out by Powell, the degradation of mountains is so rapid that only young mountains can be lofty. The St. Elias Range is not only lofty but steep, and its rate of waste must be rapid. The fact that it is lofty despite rapid waste indicates that its waste is compensated by growth.
In view of the differences in general geologic history, there need be no surprise if the Pleistocene history of the district of high mountains should differ from the Pleisto- cene history of the districts of Alexander Archipelago and Prince William Sound. In view of the loftiness of the mountains, it is rather probable than otherwise that uplift has occurred since the epoch of chief Pleistocene glaciation. It is therefore inferred with some confidence that the discordance between the sea-level indicated by the rampart moraines and the present sea-level has been brought about chiefly by local uplift of the land.
If this view is correct, the disturbed marine clays ob- served near La Perouse Glacier (fig.22) may be con- nected with a fault zone of Pleistocene or post-Pleistocene date.
PRINCE WILLIAM SOUND Prince William Sound is a very irregular bay, opening southward (pl. x1). All about it are mountains, the higher being massed at the north, and others encroaching on its area as promontories and islands. The largest islands,
1 National Geographic Mag., vol. 3, pp. 171-172, 1891.
174 ALASKA GLACIERS
Montague and Hinchinbrook, lie at the south, separating the sound from the open ocean. The inlets of the north- ern coast, some of which we visited, are fiords, abounding in evidence of glacial sculpture, and the lower slopes of the as-
FIG. 82. PENINSULA NEAR ORCA, PRINCE WILLIAM SOUND.
Shows the glacial rounding of mountain crests, fifteen miles from the ocean.
sociated peninsulas and islands are well rounded. On the east side of the sound the rounding extends to an estimated height of 3,000 feet, in Columbia Bay, at the north, to about
* FIG. 83. HINCHINBROOK ISLAND, FROM THE SEA. Shows a serrate crest line, little, if at all, modified by overriding ice.
4,000 feet, and to the same or greater height in Port Wells. Seaward the height diminishes and the higher crests of the outer islands are comparatively angular and serrate.
PRINCE WILLIAM SOUND 175
It is probable that Pleistocene ice occupied the whole sound, but nothing is known of its seaward limit.
In College Fiord, a branch of Port Wells already de- scribed (page 81), there is a magnificent system of hanging valleys, the larger being still occupied by glaciers, which enter the fiord with ice cascades. These side glaciers have accomplished something in the way of erosion since the disappearance of the trunk glacier to which they were once tributary, so that they do not rest upon the un- modified face of the fiord wall, but occupy shallow chan- nels. In a general way the surfaces of the glaciers, in their lower courses, are flush with the adjoining portions of the fiord wall.
My attention has been directed by Gannett to the fact that several of the cascading glaciers make two leaps, and that there is a certain amount of harmony in the spacing of the falls. When the region shall have been thoroughly studied it is possible that the interpretation of these corre- spondences may develop a special chapter in the history of the ice retreat.
With the aid of a series of photographs made by Mer- riam, I have computed the approximate heights of the more important cascades, as follows: Wellesley, 1,700 feet; Vassar, 2,200; Bryn Mawr, (trunk) 1,300, (left branch) 2,700, (right branch) 2,500; Smith, 1,250, 1,700
Well Vas. BM. Smith Red
FIG. 84. DIAGRAM OF NORTHWEST WALL OF COLLEGE FIORD.
Short horizontal lines show the relative positions of the cascades of Wellesley, Vassar, Bryn Mawr, Smith and Radcliffe glaciers. S.L. sea-level. Scale, 14,000 feet =1 inch. Com- pare figures 44 and 45.
and 2,600; Radcliffe, 1,800 and 3,500. When these are platted to scale in their proper vertical and horizontal re- lations (fig. 84) they fall into two series, descending south- ward from the head of the fiord. Making some allowance
176 _ ALASKA GLACIERS
for the greater volume of the side glaciers when the trunk glacier filled the fiord, I have indicated the profile of the trunk glacier by a dotted line (as). The inclination of this line from the horizontal is about 2°, or one in twenty- five. Its height above tide ranges from 2,800 to 4,800 feet, and it indicates a thickness of ice exceeding these figures by the depth of the fiord, whatever that may be. In the line of Gannett’s suggestion, a second tentative profile (cp) is drawn in similar relation to the crests of the lower series of cascades.
The depth of ice indicated by the hanging valleys is somewhat less than that which would be inferred from the rounding of projections, and it seems probable that the epoch during which the hanging valleys received their principal sculpture was not the epoch of maximum glaciation.
A cordon of high hanging valleys surrounds Harriman Fiord. Above Barry, Serpentine and Surprise glaciers they contain hanging glaciers at a general height of about 4,000 feet, and east of Harriman Glacier their ice banks coalesce in a continuous terrace along the valley wall (page 95). ‘The surface of the trunk glacier to which they are adjusted probably lay 5,000 feet above present sea-level.
On the north side of Montague Island and at various points on the peninsulas of the east and west sides of the sound, a horizontal terrace was observed, at an estimated height of 50 to 75 feet above tide. No near view was obtained, and I did not learn its character.
As the Pleistocene glaciers extended at least to the outer coast line, as their work of erosion was great, and as their limit is not indicated by conspicuous moraines, the provisional inference is made, as in the discussion of the Alexander Archipelago, that the ocean surface was com- paratively low at the time of their greatest expansion and that their outer moraines are now submerged.
KADIAK ISLAND 177
KENAI PENINSULA
My observation of the Kenai Peninsula was restricted to the northwest side of its more southerly arm. It is there constituted by a lofty upland partially dissected by large trenches, some of which now contain glaciers. Its upper parts have a comparatively mature topography, and seem to constitute remnants of an ancient pene- plain, which has been bodily uplifted, with some disturb- ance of original horizontality. The plateau resulting from this uplift was deeply trenched along the main lines of drainage, and the valleys thus opened were modified in characteristic manner by Pleistocene glaciers. They are now U-troughs, and some are partly submerged, so as to constitute fiords. On the side facing Kachemak Bay and Cook Inlet, it was evident that the old glaciers extended beyond the position of the modern coast line, but nothing was seen to indicate their outer limits.
KADIAK ISLAND
Kadiak Island is 100 miles long and 50 miles broad. Its longer axis, trending northeast, is parallel to the neigh- boring coast of the Alaska Peninsula, from which the is- land is separated by Shelikof Strait, 30 miles wide. Afog- nak Island, a close companion of Kadiak, continues its northeasterly trend; and the Barren Islands serve as physiographic stepping stones to connect the group with the axis of uplift following the oceanic side of Kenai Peninsula.
The island is mountainous throughout, but contains no lofty range. As on the Kenai Peninsula, the summits tend toward uniformity and an even sky-line, and there are remnants of an ancient uplifted peneplain. Such lowlands as we saw are of moderate extent and uneven surface. The coast line is sinuous, and some of the nar-
178 ALASKA GLACIERS
row bays may properly be designated fiords, although _ less strongly characterized than those of southern Alaska.
Opportunities for personal observation included near views of the northern coast, a brief landing near the west- ern extremity, and a longer stay near the eastern extremity, with Kadiak Harbor as a base of operations.
Our landing at the west was on a part of the coast fa- cing Shelikof Strait, west of Sturgeon River. The view was limited by a fog, but I was able to recognize two narrow U-troughs with simple contours. The ridge be- tween them, composed of granite rock, was seen to have a narrow, straight crest; and a parallel ridge, less clearly revealed, appeared to be of the same character. The troughs were evidently shaped by glacial ice, and the nar- rowness of the intervening crest indicates that the chief work was done by valley glaciers, rather than by an over- riding ice-sheet.
Thirty miles farther east we entered the mouth of Uyak Bay, a long inlet heading south of the middle of the island but opening northward. The mouth lies among hills or low mountains, whose thorough rounding indicates com- plete flooding by Pleistocene ice. ‘Toward the interior I could see mountains, several thousand feet high, whose blunt summits told of ice-scoring, and beyond them loftier peaks with angular crests. ‘The slopes bordering the bay descend steeply to the water, and there is no foreland, but the sweeping curves characteristic of the typical fiord are wanting. No accumulations of drift were seen.
Steaming north from Uyak Bay and then eastward, we passed two large projections of the coast, one a peninsula (Ugat) and the other an island (Uganuk), and the extrem- ities of these were thought not to be glaciated. On the peninsula are hills with ragged summits, apparently crested - by outcropping igneous dikes.
Straits separate the north end of the island from three
KADIAK ISLAND 179
smaller islands, all mountainous. Traversing the straits, we found familiar signs of ice work: on Raspberry Island a straight wall with hanging valleys; on the Kadiak side a general rounding of all summits up to the clouds, which hung at about 2,000 or 2,500 feet. Here, too, the water is bordered in places by a lowland or terrace (fig. 85), carved, for the most part, from vertical slates. In detail the lowland is uneven, and it is locally broken into islands, but its general plane is easily traced and, as already noted by Dall,* inclines from east to west. The height ranges from about 100 feet to sea-level.
At the extreme east lies Chiniak Bay, a broad opening, invaded on one side by mountain promontories, and partly
FIG. 85. TERRACE ON SPRUCE ISLAND, OPPOSITE KADIAK ISLAND.
sheltered from the ocean by a group of low islands. Close to the islands is the village of Kadiak. The general trend of promontories and islands is northeast-southwest. The islands are shredded remnants of a plain carved from ver- tical slates, probably a base-level plain contemporaneous with the terraces along the straits (fig. 86). Their uneven surfaces include rounded hills about 100 feet high, but the plane of the original peneplain must pass above these. All surfaces about the bay are glaciated. The island topography is moutonnée, with a large pattern, individual bosses being sometimes half a mile or more in length. A few patches of glacial polish and striz were found, though such records have been generally obliterated by weather-
1 Seventeenth Ann. Rept. U. S. Geol. Survey, part 1, p. 863, 1896.
ALASKA GLACIERS
ISLANDS OFF KADIAK.
FIG. 86. The observer stands on a promontory of Kadiak Island at a height of 1,000 feet and looks eastward. At the left is the village of Kadiak, built on a slo-
ping foreland. Islands and foreland are remnants ofa peneplain. See page 179.
ing. The valleys be- tween promontories of the mainland are U-troughs. The steep hill back of the village, a mass of slate, is smoothed and fluted on a grand scale, its original topography being so completely remodeled that its drainage seeks new routes and is engrav- ing narrow canyons across the rounded slopes (fig. 87). Northwest of this hill stands a higher ridge, where the upper limit of ice-rounding is seen to be about 3,000 feet above tide, and where several hanging val- leys overlook a finely sculptured trough (fig. 88). It is evident that a confluent ice-sheet, enveloping all but the highest summits, here flowed to the north- east, with a thickness, along the present coast line, of 2,000 to 3,000 feet. No important masses of drift were seen.
KADIAK ISLAND 181
While these observations cover but a small part of the island, they are so distributed as to throw considerable light on Pleis- tocene con- ditions. The glaciation of the eastern, northern and western ex- tremities of the island, and the notable
A h e i g h t.ta FIG. 87. HILL BEHIND KADIAK VILLAGE. Showing glacial sculpture and subsequent erosion by a stream.
which ice sculpture extends at the east and north, indicate a practi- cally continuous glacial envelope, from which scattered peaks pro- jected as nunataks. Afognak and the other im- portant is- SN lands of the = ¥. ih 7 i a group were
2 wr probably in- NC SSE] cluded in the 4 same envel- : | ope, and the “ice extended in many di- rections be- yond the po- sition of the present coast line. The apparent absence of glaciation from salient features of the northwestern coast indicates
FIG. 88. HANGING VALLEY NEAR KADIAK VILLAGE. The lower ground was shaped by . large glacier moving from left to right.
182 ALASKA GLACIERS
that the ice-sheet of the island was not an overflow from the mainland, for mainland ice could not have crossed the island without burying deeply the whole northwest coast. And the same interpretation may be given to the narrow-crested ridge observed between glacial troughs at the west, for a strong overriding current would have flat- tened the crest. The relation of land to sea in Pleistocene | time is not shown, but remnants of a low base-level plain indicate a pre-Pleistocene period of stability, during which the attitude of thé land was slightly different from the present, the eastern side of the island being somewhat lower than now.
The reasoning tending to show that Pleistocene glacia- tion was associated with a low sea-level applies to the south coast of Kadiak with even more force than to the district of Prince William Sound, for the island, standing forward beyond the general line of the Alaska coast, is specially exposed to the influence of the great ocean current.
REGION OF THE GULF COAST
Fragmentary as were our observations in the districts we have already described, they were still more fragmen- tary in those touched farther west and north, and the pres- ent is therefore a convenient point for retrospect and summary. The district of the Alexander Archipelago, the district of high mountains, the district of Prince Wil- liam Sound, Kenai Peninsula, and Kadiak Island, circle about the Gulf of Alaska. A curved line passing through them is more than 1,000 miles in length, and its extremities are goo miles apart.
In the high mountain region the Pleistocene glacial system seems to have included alpine glaciers similar to those of the present time but larger; and these united ina system of piedmont glaciers, or possibly in a confluent piedmont glacier, which everywhere reached the sea. In
REGION OF THE GULF COAST 183
the other districts the Pleistocene glaciers were confluent, extended beyond the line of the present coast, and prob- ably reached the sea, although their limit is undetermined. In the high mountain region there has been post-glacial uplift of the mountains, and in connection with that uplift great moraines, which were probably formed at the water’s edge, have become part of the land. In the other districts the apparent absence of similar great moraines is pro- visionally explained by the hypothesis that the sea surface then lay lower with reference to the land and that the subsequent submergence of a portion of the land has con- cealed the zone of morainic deposit.
Assuming that a change has transpired in the relation of land and sea since the epoch of maximum glaciation, it is of interest to inquire whether that change was a sinking of the land or a rising of the sea. The general theory of the subject has not yet reached such a condition as to afford a satisfactory answer, but, on the contrary, is so unsettled as to find advantage in every local determina- tion of the nature of the change which may be made on independent grounds. In the case of the high mountain district, the geologic recency of orogenic movement is indicated in other ways, and the post-Pleistocene emerg- ence of land is therefore referred with confidence to land change rather than water change. In the other districts we have no evidence of recent orogenic change, and the mountains appear to have been produced by the dissec- tion of broad plateaus. The uplands about the Alexander Archipelago and Prince William Sound, and those of Kenai Peninsula and Kadiak Island, all contain traces of uplifted peneplains, the uplift having occurred so long ago that the resulting plateaus were profoundly sculptured before the advent of Pleistocene glaciers. The districts of the Alexander Archipelago and Kadiak Island are also characterized by peneplains near present sea-level; and
184 ALASKA GLACIERS
low terraces observed in Prince William Sound are pos- sibly of the same order. It is, furthermore, probable that the pre-Pleistocene dissection of each area was continued in association with a comparatively low base-level. In view of the large number of common elements, the whole region, with the exception of the high mountain district, may be provisionally regarded as a unit in its later geo- logic history. The uplifted peneplains do not all stand at the same height, and there are important differences of altitude within individual plateaus. ‘These local differ- ences suffice to show that not all changes can be ascribed to the sea, and make it probable that the plateaus were created by changes originating within the earth’s crust. The low peneplains also show minor discordances, and while these also must be ascribed to crustal movement, the fact that they are of moderate amount is, on the whole, indicative of general crustal stability. It is a note- worthy, and probably significant, fact that the oceanic base-level of the region, after resting for a long time at the height indicated by these low peneplains, dropped below them at the time of the excavation of the fiords and then returned to approximately the same position. If this oscillation was an oscillation of the land, it was of the broad or epeirogenic type, and the association of wide extent with approximate uniformity of position after the completion of the cycle is most remarkable. It would seem probable that so great a general movement of the earth’s crust would afford opportunity for the relief of local strains, and thus be accompanied by important differential movements. On the other hand, sensible uni- formity for any region of the magnitude here considered would theoretically be a characteristic of an oscillation of the sea. The local evidence, therefore, seems to me more favorable to the hypothesis that the sea was low during the fluvial and glacial erosion of the fiords and has
UNALASKA ISLAND 185
since risen, than to the hypothesis that the land was then high and has since subsided.
UNALASKA ISLAND
On two occasions we spent a few hours at Dutch Har- bor, making short excursions in the immediate neighbor- hood, and we also sailed along the north coast on a foggy day. The opportunities for observation thus afforded were much more limited than those enjoyed by Russell,’ and my notes are chiefly of service as affording verifica- tion of his description. The north coast, west of Cape Cheerful, is faced by a high sea cliff which testifies to rapid aggression by waves. The cliff shows in cross- section a number of U-shaped valleys, and these, so far as the fog permitted us to see them, have the simple contours characteristic of complete adjustment to the conditions of ice flow. Several of them end hundreds of feet above the sea, this condition being manifestly due to truncation by the receding shore cliff. One of them reaches the shore at tide-level, and the walls of that one seemed to be sheathed with a layer of drift in which post-glacial rills and brooklets have cut narrow gashes. The shore cliff also truncates, at rather high levels, a few V-shaped gorges, and the association of these with the glacial troughs gave the impression that the Pleistocene glaciers were of alpine type and not confluent. As the mountains were concealed by fog, I was unable to observe the cirques of which Russell makes mention.
The forms of the hills about Unalaska Bay are not typi- cally glacial, but, on the other hand, they are not con- structional (with a single exception), and if products of atmospheric waste, they are of unusual type. The single constructional form is a young volcanic cone near Cape Cheerful. The other hills are also of volcanic rock, but
1 Bull. Geol. Soc. Amer., vol. 1, pp. 138-140, 1890.
186 ALASKA GLACIERS
give little suggestion of the original mountain forms from which they were derived. They are irregular alike in their larger and smaller features.
If the forms of land in this part of Unalaska Island were constructional, the sinuosity of the coast might be ascribed to irregularities of volcanic eruption; but as they are ero- sional, the deep embayments between steep-sided points and islands, and the dearth of plains near sea-level, point toward a somewhat recent subsidence of the land or rising of the sea.
Spurr describes a series of terraces near Unalaska Bay, ranging up to a height of 1,500 feet, ascribes them to marine action, and infers a gradual rising of the land in late Pleistocene time.’ He notes also that the village of Iliu- liuk stands ona spit which is evidently of recent formation but is shown by its vegetation to be above the reach of storm waves, and infers that elevation of the land is now in progress. The last mentioned observation I was able to verify, but I was not satisfied that any higher terrace I saw had been formed by the sea.
BERING SEA
The most extreme and contrasted opinions have been advanced with reference to the Pleistocene condition of Bering Sea. It has been stated by one high authority* that the western coast of Alaska, the eastern coast of Siberia, and various islands of Bering Sea, are all glaciated in such a way as to indicate the occupation of the eastern part of the sea by an ice-sheet; and it has been asserted
1Kighteenth Ann. Rept. U. S. Geol. Survey, Part 11, pp. 266-267, 273, 276, 1898. 2John Muir. On the Glaciation of the Arctic and Subarctic Regions visited
by the U. S. S. Corwin in the year 1881. Rept. Cruise of the Corwin, 1881, Washington, 1885. .
BERING SEA 187
by another high authority’ that there are no evidences of glaciation, either general or local, on these various coasts and islands. A third investigator,’ also of high rank, ascribes the fiords of the Siberian coast to glaciers, but finds no evidence of glaciation on the neighboring coast of Alaska about Port Clarence. My own opportunities for observation were limited to a few hours each on St. Paul, St. Matthew and Hall islands, a few hours sailing past the Siberian coast, with a brief landing in Plover Bay, a distant view of Cape York, a point southeast of Cape Prince of Wales, and a few hours on the tundra near Port Clarence. The scanty facts thus gathered can not be expected to settle the vexed question; but, in view of the wide diversity of existing opinion, it appears worth while to make record of even hasty observations and first im- pressions.
Of St. Paul Island we saw the southern peninsula. The land is there composed of remnants of volcanic cones
FIG. 89. CRATER RIM ON ST. PAUL ISLAND. Shows projections which would not survive glaciation. Photograph by U. S. Coast Survey.
whose softened profiles indicate long-continued weather- ing. The forms are smooth, except where cut by the sea
1W.H. Dall. Bull. 84 U.S. Geol. Survey, p. 258, 1892. Alaska and its Re- sources, pp. 461-464, 1870.
2A.E. Nordenskiold. The Voyage of the Vega. New York ed., pp. 569, 583-585, 1882.
188 ALASKA GLACIERS
or varied by traveling dunes of lapilli. To my eye they conveyed no impression of ice sculpture; I saw neither the long parallel grooves and ridges which glaciers some- times carve from homogeneous rocks, nor the groups of moutonnée bosses which they usually develop where rocks are of varied texture. On the main part of the island are younger cones with well-preserved craters, and photo- graphs show that with these are associated crags such as an overriding glacier would not spare (fig. 89). Neither is it to be supposed that the craters themselves would survive the erosive action of a great ice-sheet. It may be affirmed with confidence that if the island was ever traversed by a glacier the crater-bearing cones are of later origin. >
St. Matthew and Hall islands are also volcanic, but without constructional forms. The period of eruption was so remote as to give time for the complete subsequent re- modeling of the surface by weathering and erosion. The coast shows a succession of cliffs, with rare bays and spits, and is evidently retreating rapidly before the attack of the waves. The higher slopes, though sometimes steep, are in general mature, and well adjusted to the con- ditions of erosion in a climate which obstructs the flow of water by clothing all surfaces with a sponge-like mantle of mossy and herbaceous vegetation. I saw nothing of the peculiar forms characteristic of glacial sculpture, but noted, on the contrary, a few blunt pinnacles projecting from the general surface and exhibiting such ragged de- tails as one does not find in glaciated regions. Figure go represents one of these which happened to come within the field of a photograph.
The ordinary landing at Port Clarence is upon a long spit, but we visited the mainland also, going ashore at a point where a gently undulating surface rises within a few miles to hills several hundred feet high. The rock is
BERING SEA 189
a highly inclined slate, and the shaping of the surface has been wholly by erosion. Except at the coast, the rocks are concealed by tundra. This spongy growth obstructs the flow of water, so that streams are rare; but we landed at one of these rare streams and had a view of its valley (fig.91). The valley is evidently one of mature de- velopment, and _ its profiles are perfectly adjusted to the associated lines of drainage. The divides are broadly rounded, but the rounding is that characteristic of inter-stream summits where the vegetal mat is close, and is distinctively non-glacial. The bed-rock here has the same physical character as that in the Kadiak region, but the topographic aspect is altogether different. About
FIG. 90. UNGLACIATED KNOB ON ST. MATTHEW ISLAND.
an ee SES ae Sane Sa: &: ft
FIG. 91. STREAM-GRADED VALLEY NEAR PORT CLARENCE.
Kadiak the hills have moutonnée forms, the hills and hol- lows have a dominant trend, and the drainage is youthful. At the Port Clarence locality the topography does not
Igo ALASKA GLACIERS
exhibit a dominant trend and all slopes are fully adjusted in harmony with the drainage.
The southeastern part of the Siberian peninsula is char- acterized by low mountains with spurs projecting seaward as promontories and alternating with fiord-like bays. The topographic details near the coast fall into three categories: (1) A system of relatively gentle slopes chiefly occupying uplands; (2) a system of relatively steep slopes chiefly exhibited in the walls of the fiords (at points of junction these are sharply contrasted with the slopes of the first system); (3) coastal features, especially shore cliffs and
FIG. 92. EAST WALL OF PLOVER BAY, SIBERIA. The sky-line follows the boundary between the steep fiord wall and the smooth topography
of the upland. A spit projecting from the end of the wave-wrought shore cliff protects the more distant part of the wall.
spits, the product of wave action under present conditions, The smoother and older topography is not altogether de- void of steep slopes, but gives an impression of close ad- justment between processes of subaerial erosion and the unequal resistances of rock masses. I saw nothing in its profiles and contours to indicate glaciation. The newer and steeper slopes are associated with the troughs con- taining the bays in such way as to suggest glacial action, but those that we passed near betrayed no smoothing, grooving, or other minor feature of glacial abrasion. The shore walls of Plover Bay are precipitous rock cliffs at top and consist of talus at base, one phase passing into the other in a manner suggesting that the original rock pro- file was somewhat similar to the one brought about by
BERING SEA IgI
partial disintegration. They run straight for long dis- tances. The chief agencies competent to produce such features are faulting and glacial sculpture, and in this case glacial sculpture appears to me the more probable agent, although subsequent weathering seems to have de- stroyed those minor details of configuration which one naturally seeks as confirmatory evidence.
There are two accessory features which lend support to the hypothesis of glaciation. In the far dis- tance, at the head of the bay, we could } see that its a7 trough is con- F=- nected with two or more
land valleys, andit was evi- F!G-93- HANGING VALLEY ON WALL OF PLOVER BAY. dent that the Figure 92 gives an oblique view of the same wall.
valley most nearly in the direct line of prolongation is dis- tinctly U-form in cross-profile and has walls of simple con- tour. The other feature is a niche, high on the wall of the fiord, having the form of a cirque or hanging valley (fig. 93). In this case I attach little weight to the testimony of the hanging valley, because it has no companion on the long line of cliffs, and therefore may possibly be a simulative form, determined by local peculiarities of rock texture; but the distant valley is distinctively glacial in habit.
It seems to me onthe whole probable that the fiords of this coast contained Pleistocene glaciers of large size, which extended farther seaward than the general line of the present coast, but that the spaces between the fiords were not covered by ice.
192 ALASKA GLACIERS
My observations on the coasts of Bering Sea may be summed in the statement that Plover Bay and neighbor- ing Siberian fiords have features indicating local glaciers of considerable magnitude, that evidence of glaciation was seen at no other points, and that certain crags and pin- nacles on St. Matthew and St. Paul islands seemed incon- sistent with the theory of a continental glacier in the Bering Sea region. My interpretations at the north agree substantially with those of Nordenskiold; at the south with those of Russell.
So far as the Port Clarence region is concerned, what I have said above has become ancient history before reach- ing the press. A delay of four years between observation and publication is fatal to novelty, if one’s theme concerns a region developing under the stimulus of the discovery of gold. Near where we landed on the shore of Port Clarence the town of Bering now stands, and all Seward Peninsula has been explored by the prospector. To aid him the U. S. Geological Survey has sent active parties of geologists and topographers; and as the proof sheets of these pages pass through my hands, I am able to examine contour maps of a large part of the peninsula, and study three comprehensive reports of geologic recon- naissance. ‘These reports are by Brooks, Mendenhall and Collier, and tell of explorations and surveys made in the seasons of 1900 and 1go1.’
They cover the general question of Pleistocene glacia- tion in a demonstrative and altogether satisfactory way. The Kigluaik Mountains, between Port Clarence and Cape Nome— mountains with an extreme height of about
1A Reconnaissance of the Cape Nome and adjacent Gold Fields of Seward Peninsula, Alaska, in 1900. By Alfred Hulse Brooks. 1901. See pp. 42-53.
A Reconnaissance in the Norton Bay Region, Alaska, in 1900. By Walter Curran Mendenhall. 1901. See p. 208.
A Reconnaissance of the Northwestern Portion of the Seward Peninsula, Alaska. By Arthur J. Collier. In press. See pp. 24-29 and 34-42.
SEWARD PENINSULA 193
4,700 feet — nourished in Pleistocene time local glaciers of some magnitude. These are attested by U-troughs, cirques, moraines, and moraine lakes. One of them passed southwestward beyond the foothills of the range, and may have reached the sea. Another approached or reached sea-level at the north. The Bendeleben Moun- tains, farther inland, also contained glaciers, but too small to push beyond the foothills. Among the York Moun- tains, which stand between Port Clarence and Cape Prince of Wales, and have an extreme height of about 2,900 feet, were probably small glaciers, but, if so, they were wholly contained in the mountain valleys. Except for these local developments, the surveyed parts of Seward Peninsula—namely, the southern and western parts— were not occupied by Pleistocene ice. Over large areas the mantle of residuary waste lies undisturbed on the rock from which it was derived; and in these areas are angular and slender crags, as well as perched boulders of disintegration, lying in their original positions. Other large areas bear rolled gravels, associated with a series of marine terraces.
One of the marine terraces described by Collier and Brooks was seen by us along the southern base of York Mountains. It is there a conspicuous bench, ending sea- ward in a steep bluff, and has a height of about 600 feet. According to Collier, its uplift has been unequal, so that the old marine plane is now a warped surface. The fact of warping also accords with my observation, for such parts of the neighboring Siberian coast as I was able to study from the ship seemed altogether free from marine terracing.
An observation of progressive modern change of level was made on St. Matthew Island. A small bay on the east shore, near Glory of Russia Cape, has been cut off from the sea by a series of shore bars. After the first bar
194 ALASKA GLACIERS
or spit was completed, another was built outside it, and so on to the number of six or more. The one next the sea has a crest considerably above high-tide, at the extreme limit reached by storm waves, and the top of it is covered by drift-wood, to which annual additions are doubtless made. The next bar, lying back of this and parallel to it, is six feet lower. It also is covered by drift-wood, but the wood is decayed, so that no sound logs were found. Two others are successively lower and have no drift- wood, and the innermost are so low as to be covered by the water of the bay. It is evident that each of these ridges of shingle was formed bystorm waves at the shore, and we may assume that its crest height was originally as far above high-tide as the crest of the outer ridge is now. The existing differences in height have resulted from the gradual sinking of the land, and a rude indication of the rate of sinking is given by the drift-wood. The inner ridges were made so long ago that the drift-wood they originally bore has rotted away and disappeared. The age of the second ridge has given time for only the partial decay of the timber upon it, and the inference is that the island has sunk to the extent of six feet in a period less than that necessary for the complete destruction of logs through the processes of decay.
CHAPTER III GENERAL CONSIDERATIONS AS TO GLACIERS
SoME of the field observations recorded in the preced- ing chapters have more than local interest in that they open theoretic questions and lead to suggestions bearing on the general subject of glaciers and their work. Certain of the suggestions have already been noted, as they seemed to belong to the discussion of the associated observations, but others may more appropriately be considered by them- selves and have been reserved for the present chapter. The general considerations already set forth refer to an annual cycle in the distal extent of tidal glaciers (p. 22), the production of features of shore topography by waves generated by the calving of icebergs (p. 69), anomalies in the variations of glaciers (p. 106), the origin of pitted plains (p. 54), and the origin and interpretation of hanging valleys (p. 114). The considerations to be presented in the following paragraphs pertain (1) to the broader char- acters of the surface of a glacier, (2) to the conditions af- fecting types of glacial sculpture, (3) to the conditions
(195)
196 ALASKA GLACIERS
of wear below sea-level, and (4) to the parallelism of gla- ciers and rivers.
THE SURFACE OF A GLACIER
Evenness as Compared to Rock Floor.— The parts of glaciers which came under my observation were the lower or distal portions, with surfaces usually less than 1,000 feet above sea-level. In these lower parts the master characters of the surface are a forward slope in the direc- tion of flow and horizontality in the direction normal to the flow, the direction of flow being inferred from the courses of medial moraines.
The configuration of the rock floors beneath the glaciers could not be directly observed, but it was possible to infer their general characters, with high probability, from what could be seen of the rock floors in front of the glaciers. Such rock floors are in all cases abandoned glacier beds, having been covered by the ice not only in Pleistocene times but, in many instances, in historic time also. As a rule these bared portions of the glacier troughs exhibit much irregularity. The fiords vary rapidly in depth; in places they are diversified by islands. ‘The land troughs have hills and hollows; and other hills jut through the glaciers as nunataks. It is therefore believed that the bottoms of the glacier channels have in general consider- able inequalities.
These irregularities are only slightly represented in the configuration of the glacier surface. The greater inequali- ties of the longitudinal profile of the bed are shown by cascades of the glacier, but inequalities of the cross-pro- file are rarely indicated by visible shapes of the ice, and bosses or hills hundreds (perhaps thousands) of feet high may fail to influence the surface. If the summit of a boss approaches the surface it produces crevasses, but the broader features of the surface contours are not changed.
THE SURFACE OF A GLACIER 197
This leveling of the surface is of course ultimately caused by gravity, and it is immediately brought about by variations in the flow of the ice, the directions and veloci- ties of the flow of different parts being so modified as to permit the ice to pass around and over obstructions with- out lifting the glacier bodily. The existence of internal variations in direction, being attested by the arrangement of striz on lands that have been glaciated, is a well-recog- nized fact, but variations of direction alone are not sufhfi- cient to explain the coexistence of an approximately even glacier surface with a very uneven glacier bed. The con- dition of continuity can not be satisfied without variations of velocity also within the mass. The adjustment of an ice stream to an irregular channel through the formation of differential currents is thus quite analogous to the ad- justment observed in water streams, although the greater viscosity of the ice may be assumed to prevent the occur- rence of reversed currents or eddies.
Another factor in the leveling of the ice surface is prob- ably connected with ablation, or the process of wasting by melting and evaporation. Portions of the Muir and Hugh Miller glaciers which were demonstrably stagnant, never- theless exhibited to the general view a conspicuous even- ness, and the same remark applies to glacier remnants stranded, like Reid’s ‘ Dying Glacier,’ on saddles, or trough summits. These motionless and wasting ice bodies, though not tabular but curved downward toward their edges, were bounded by simple symmetric contours, in- dicative of equable reduction by the wasting agents and a general interdependence of process for the whole surface.
Lateral Cliff.— Coexistent with the general tendency toward evenness are several kinds of unevenness, each determined by some evident special condition. Wherever the side of an ice stream was observed adjacent to a rock wall, it was found to present a cliff toward the rock, the
198 ALASKA GLACIERS
ice cliff and rock wall constituting the sides of a narrow valley or fosse, usually 50 to 100 feet deep. A stream of water sometimes followed the valley. This feature, fa- miliar in all glacier districts, has been explained as due to the heat acquired by the rock through insolation and then conveyed by radiation to the adjacent ice; and the stream of water, when present, would help to account for the valley, for so much of its volume as came from the sun- heated rock would be warmer than the water of ablation and have some power to melt ice.
Crevasse Cycle.— Wherever the work of the sun is not complicated by the presence of rock débris, the inequali- ties initiated by crevassing are carried by ablation through a regular cycle of change, ending in their complete re-
3 na Sh
fe!
eee BSS ty Rhee. yi mis * +m. ra « at Ps Nu, Ee fer “ec ny OPA Fag ag . 4 cea ee
1800,
FIG. 94. DOWNWARD LIMIT OF CREVASSES IN MUIR GLACIER. The lower part of the ice is undivided; the upper is split into slabs and columns. The dark hill in foreground is of ice with a cover of gravel, a remnant of the retreating glacier.
moval. In the crevassing which begins abruptly at the head of a cascade, the cracks divide the ice into flat- topped, elongated blocks, usually tapering toward the ends and more or less connected at the surface by slender masses analogous to the slivers of half-broken timber. Whatever the distance downward to which the cracks may originally extend, the resulting permanent crevasses have
CREVASSE CYCLE 199
only moderate depth, the ice being welded into a practi- cally continuous mass beneath. Wherever a crevassed tract was exhibited in section in a tidal cliff, the crevasses were seen to terminate uniformly along a definite zone, which was usually nearer the top of the cliff than its base. The depth of this zone was estimated in different instances at from 50 to 125 feet, but this did not represent the full original depth of the crevasses, as something had in every case been lost by ablation (fig. 94).
AAs soon as the cracks are opened, melting begins on
FIG. 95. CREVASSES AND SERACS, MUIR GLACIER.
their faces, the rate being greatest above, and the flat tops of the ice blocks, the sevacs of alpinists (fig. 95), are converted into roof-like crests and pinnacles. In this condition the surface is nearly or quite impassable (fig. 96). With continuance of ablation the height of the seracs is reduced, their slopes become less steep, and many connecting cross ridges become available to the wayfarer, so that with the exercise of care and patience one can make his way safely in any direction. Figure 97 shows a characteristic field of this sort, crossed by some of our party on their way to the great nunatak of the Columbia Glacier. A continuance of the same reduction by ablation eventually obliterates the ice waves alto-
200 ALASKA GLACIERS
gether, leaving a plain surface over which progress is absolutely unimpeded (fig. 98).
FIG. 96. PINNACLES ON COLUMBIA GLACIER.
Thus the cycle of ice degradation by ablation is strictly analogous to the cycle of land degrada-
EZ ig tion by erosion; Ziggy YL LZL SE an original
plain is rapidly
=
Liye eine ‘ ‘Up == —-.-> converted into
=
$56 a region of highly acci- dented topog- raphy, which slowly returns to the plain condition through the removal of its promi- nences. If the cycle is interrupted by the formation
of a new system of crevasses, the analogy still holds,
FIG. 97. BACK OF COLUMBIA GLACIER. Illustrating gradual smoothing of surface.
CREVASSE CYCLE 201
for the features of the new cycle thus instituted at first combine with those of the old and eventually supplant them.
As my excursions on glaciers were all short, it hap- pened that I never saw a complete illustration of the ablation cycle on one gla- cier, but such examples should be readily discover- able. Where the even bed of a glacier increases its grade, where it is interrupted PEPER by a step, producing a CaSs- The rock retards the melting of the ice on ca de, or where the overrid- which it rests, and thus preserves a pedestal. ing of a submerged peak produces breaking strains in the upper part of the ice stream, the smooth ice plain above, the prismoidal blocks, the acute peaks, the gradually subsiding waves, and the final ice plain
FIG. 98. LEVEL TRACT ON MUIR
Wann. Het! ero SHEET Tsp gay
FIG. 99. IDEAL PROFILE AND SECTION should appear in reg-
ws Ns abate 9 ular sequence, sub-
Illustrating the formation and obliteration of crevasses ‘ = re stantially as repre
sented in figure gg.
An exceptional condition was observed on the tongue of the Columbia Glacier which flows into the western embay- ment of its valley. A plain surface was there interrupted by an extensive plexus of crevasses, which were filled to the brim with water and snow (fig. 100). The normal cycle appeared to be varied in this case by a lack of drainage, surface ablation progressing only where the air had access, and truncating the seracs down to the water- line. It is conceivable that under such conditions a set of crevasses originating from horizontal stresses may pro-
202 ALASKA GLACIERS
duce no crests and pinnacles, but remain as mere inter- ruptions of a general plain surface until obliterated by progressive ablation.
This exceptional condition draws attention to the fact that crevasse systems are normally underdrained. Look- ing into crevasses on a warm day, one may sometimes see the water of ablation in slender rills disap- —'} pearing down tunnels or shafts in
FIG. 100. IDEAL sEcTion or the compact blue ice below — to WATER-FILLED CREVABSES AND. he pathered Goubtiess in eapiacia: TRUNCATED SERACS. *
or subglacial streams, and eventu- ally escape at the end of the glacier.
Where the ice carries a heavy back-load of drift the normal crevasse cycle is greatly modified (fig. 101) and its completion indefinitely postponed.
: ‘ : Ly nt
As already mentioned in connection , Hara yer with the Hidden Glacier, the drift |§J7ict light at é cee pi et
falls into the crevasses and gathers at ‘= - their bottoms. As the intervening
. rit = Fj
ice blocks acquire acute crests the 5 Vi nat eh Ti : ; aye! { x ae va ity
greater part of the drift rolls and ra sr ilet Ae
slides from them, and they retain only enough to darken the surface. Under the familiar law that a sprinkling or thin cover of drift promotes melting, while a heavy mantle retards it, the pinnacles are rapidly reduced, and "% 10%: “SeLuRNS h . : ll d d OF DRIFT ON SURFACE their sites are eventually depressed ....,,cven ov Gian below the dritt masses accumulated _ Crevasses formed in drift- z ae Ke F covered ice (a) accumulate the inthe crevasses. The original asperi- arift (2), and eventually be- ties made by the crevasses have now °™* ‘Re Sites of Bilis (¢).
been destroyed, but a secondary system has been evolved, which tends in similar manner to produce a tertiary sys-
tem, and so on indefinitely. Wherever we found a broad
GLACIAL SCULPTURE 203
tract of ice heavily loaded with drift, its surface was made up of hummocks and hollows, varied here and there by cliffs of black ice, down which pebbles and boulders oc- casionally rolled in shifting their position from hill to hollow. These irregularities, involving, as they do, in- equality in the distribution of the drift on the surface of the ice, help to account for the irregularity observed in terminal moraines.
GLACIAL SCULPTURE
The work of rock sculpture accomplished by the middle and lower parts of a glacier is performed chiefly by the pro- cesses of abrasion and plucking. Inabrasion, fragments of rock held in the under part of the ice, being dragged over the fixed rock of the glacier bed, file away and reduce it. In plucking, blocks of bed-rock, being partly surrounded by the ice, are forced from their bearings and rolled or slidden forward. If the plucked blocks have originally stood as projections, they may be broken away, even if quite firm and flawless; otherwise it is probable that they can be removed only if originally separated by joints or other structural partings. The waste resulting from abra- sion is clay and sand; plucking yields boulders.
One of the chief factors on which the rate of abrasion depends is the velocity of the moving ice. If the bed- rock surface is uneven, the ice does not flow over all parts of it at the same rate, but moves slower in the hollows and faster across the prominences. This difference results partly from the condition of continuity, which demands higher average speed where the cross-section is less, and partly from the tendency of parts embayed in hollows to lag behind the general mass. The prominences are there- fore abraded more rapidly than the adjacent hollows, and the profile is thus reduced to simple forms.
Another factor on which rate of abrasion depends is
204 ALASKA GLACIERS
pressure; the abrasion is more rapid as the pressure of the glacier against the bed-rock is greater." The resistance which the moving ice, through its viscosity,? opposes to change of form, causes it to press unequally on different parts of an uneven bed, and to abrade most rapidly those parts whose prominence compels the ice to change its direction. Thus in a second way there is a tendency to reduce the profile of the bed to simple forms.
The amount of resistance developed by viscosity de- pends on the rate of deformation; more force is necessary to deflect the ice quickly than to deflect it slowly. The parts of the bed which cause the most abrupt turns are therefore subjected to greatest pressure and to greatest wear, with the result that the profiles of the bed eventually become curves of large radius, adjusted to slow bending of the moving ice.
If the general motion of the ice is very slow, the resist- ance developed by viscosity is small and the resulting sculpture curves have comparatively small radius. If the ice moves rapidly, the sculpture curves have large radius.
1There are two theoretic limits to the law that abrasion increases with pres- sure. It has been argued by N.S. Shaler that because the melting temperature of ice is lowered by pressure, the basal part of a thick glacier must consist of water
instead of ice (Outlines of the Earth’s History, pages 237-239, 1898); and such ‘pressure-molten’ water would manifestly be powerless to grind rock waste
against the rock bed. G. F. Becker has suggested to me in conversation that
where the pressure is great there also the elastic limit of the ice is far exceeded and the ice should be expected to flow about rock fragments so as to incorporate them in the glacier and reduce or destroy their effectiveness as tools of abrasion. These considerations are not included in the above analysis because, while I do not see my way to their satisfactory discussion, I fail to perceive that they help to explain the phenomena of ice erosion as seen in Alaska. Whatever their in- fluence may be, it has not prevented exceptionally great erosion in places where the Pleistocene ice was exceptionally deep.
2In untechnical usage the word véscostty is ambiguous, being applied to a property of liquids opposed to mobility and to a property of solids opposed to rigidity. In the present paper it has the technical meaning given by the physi- cist, and is the property of fluids and solids in virtue of which internal dif- ferential movement, or shear, consumes time. The greater the viscosity the slower the yielding to a given shearing force.
te
= _ a j Se ey Oe lL oF
.
GLACIAL SCULPTURE 205
The tendency toward curves of large radius is more effect- ive where the material of the bed is easily worn than where it is obdurate.
A third factor affecting rate of abrasion is the material abraded. Some materials yield more easily than others and are worn more rapidly. Where the material of the glacier bed is heterogeneous, including both yielding and obdurate rocks, there is a tendency to hollow out the yielding rocks and leave the obdurate masses prominent. This tendency is opposed by those arising from the vis- cosity of the ice, and the type of the resulting sculpture in each individual case is a compromise. It is thought that the relative importance of viscosity is greater with swift-moving ice than with slow-moving ice.
A fourth factor is found in the quality and quantity of the abrasive material, the rock particles set in the base of the ice. The particles picked up from shale would not be effective in grinding quartzite, but particles from quartzite would act vigorously on most other rocks. The abrasive action of pure ice is probably nil. The influence of this factor is not easily formulated, but there can be no question that it qualifies the influence of other factors in important ways.
The sculpture wrought by plucking differs notably from that due to abrasion. The plucking of a block of rock removes a projection and leaves a hollow. A sur- face which has been reduced chiefly by plucking abounds in salient and reentrant angles, and would be called hackly if its pattern were smaller. Usually its salients, and often its reentrants, are rounded by subsequent abra- sion, producing a topography to which Saussure’s title of moutonnée is peculiarly applicable.
The conditions which locally determine plucking rather than abrasion are not clear to me. Evidence of plucking is seen more frequently on hard rocks than on soft. The
206 ALASKA GLACIERS
clearest examples are on salient masses, but this may be merely a question of exposure, for the finest illustrations of abrasive sculpture are also onsalients. Where a heter- ogeneous rock bed acquires an uneven surface by abrasion, the prominences of obdurate rock would be specially ex- posed to plucking, and it is easy to understand that pluck- ing may be combined with abrasion in the reduction of such a tract.
The unevenness produced by plucking is a minor feature of the sculpture topography. When greater features are considered it is evident that plucking as well as abrasion is more active on salient than on reentrant profiles, for how- ever hackly an ice-worn hill may be in detail, its general profile and contours have the same sweeping curves which characterize the products of abrasion.
The preceding discussion, which for brevity has been given somewhat deductive form, is largely based on field observation, being the result of an endeavor to understand the varied phenomena of sculpture observed in Alaska. In a region where the evidence of great glacial erosion is overwhelming, where multitudinous hanging valleys, the general obliteration of spurs from the sides of U-valleys, and the dominant and thorough rounding of crests and corners of hills and small mountains, testify to an enor- mous amount of glacial degradation, it was a matter of surprise to find the reduction of the surface to smooth- sweeping curves a somewhat rare phenomenon. By far the greater number of well-exposed glaciated areas, even where the degradation has been profound, abound in low embossments and in more or less angular groins or re- entrant spaces showing little trace of abrasive action. These surface characters presented themselves as facts requiring explanation; and I have come to regard them as indications of the great importance of plucking in the work of glacial erosion.
re =
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PLATE Avil
“Vevwe sortonimorg atow-99i 18 eworle bavorgst0t afT seg. 5 ee aij] .toioslD miC1 odd to dioe jeuy polls V tiuM to [lew sano ont to ta S20 © ze. asd ai spusiole el bia msse-qu oft mont boewsiv
rts EP ome re aes ’ : > ota / ee ee ne A
ee |S > ae Mk age (
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wees eile are on salient sismalll, bait this may mere! question of exposure, for the finest iliustrat io s of sbemaisil sculptixe dre also on salients. Where a oe . . | ceneous rock bed acquires an uneven surface by abr: the prominences of obdurate rock would be specially e : posed to plucking, and it is easy | to understand that pluc we : ing may be combined with. abrasion. in the ‘Feduction( such @ tract : The “ARERR HON OR DY of the sculpture topography. ie picvinete | 6 -Guactarep Rocks ~ as well as ab Upper Figure.—A portion of the'east wall of the valley son sin i ie Rater sare Pas. 899. and were probably pias tie century ago The dretion ae
movement was from left to 207... yy) : fy The pes of re Gat : tbe as Sretes iby a: rap
bert, uit SOPRESY oy ae ESS SS fb ited States Geo Surveyose rvation, berg the reat of ape Lower Figure. —The foreground welsieandiiaedhia of the gaat mee of Muir Valley, just south pe PD omega | views i tae ced yea cetry t was probably cove tury ago The eine vane ioe |
of hw peg an i at i : alee #ué : ° avian itp sh 2 ferdene “Sa er Photographed by G. June: Negative sai United ranaerbibiibe der de mist it was. a waatter @ surprise to find the reduction of the surface to smootm sweeping curves a soméwhat rare phenomenon, Bye the greater number of well-exposed glaciated areas, eam where the degradation has been profound, abound im ia™ emihossments and in more. or less angular groins ora entrant spaces showing little trace .of. abrasive th . hewe surface characters presented themselves as i “a ping explanation; and I have come to regard Gy fieaifons of the great importance of plucking i int
& <i aiaeantt erosion,
ae
H, A. E. VOL, Ill PLATE XVIiil
ee
ve da le ln ig
GLACIATED ROCKS
HELIOTYPE CO., BOSTON.
GLACIAL SCULPTURE 207
The importance of plucking may also be inferred, as in fact it has been by Dana, from the abundance of boulders in the moraines of an ice-sheet. In the waste deposited by an alpine glacier it is not easy to discriminate plucked boulders from the boulders which have fallen to the ice from adjacent rock slopes and been carried for- ward as back-load, but the waste carried to the edge of a great ice-sheet like the Laurentide has all been picked up as well as transported by the ice. <A portion of such a body of waste must be referred to the mantle of resid- uary and alluvial débris found initially on the land by the expanding ice mass, and this portion of course includes a contingent of boulders; but there is no reason to regard this factor as of great importance. It is probably much more than offset by the destruction of boulders in the glacial mill, for in the making of the rock flour which constitutes the body of glacial till, the abrasion of the coarser waste carried by the bottom ice may approach, or even exceed, the abrasion of the rock floor. While these various factors do not admit of definite valuation, I think it fair to say that the ratio of boulders, on the one hand, to clay and sand, on the other, in the waste deposits as a whole, is something less than the ratio of plucking to abrasion in the erosive work of such an ice-sheet as the Laurentide. |
The study of this subject made such slow progress in the field that opportunities for good photographic illustra- tion were not improved. The views reproduced in plate XVIII were taken to show abrasive work, and illustrate plucking only incidentally. ‘The upper view looks up the wall of Muir Inlet. It shows stratified rock, with a boss of more massive, possibly plutonic, rock beyond. A century ago all the stratified rock was covered by Muir Glacier. At the left near the sky-line the strata are seen to be obliquely truncated, and the plane or nappe of trun-
208 ALASKA GLACIERS >
cation can be traced across the view. It really includes the foreground, at least down to the mantle of moraine; and it is part of the wall of the glacier trough, wrought by the ice into curves of large radius. But the detail of this erosion plane, shown in the center of the field, is distinctly hackly, as though (and probably because) the degrada- tion of the stratified rock was accomplished largely by the breaking away of blocks. The prominent angles and edges of strata are abraded and highly polished on their stoss sides, but their lee facets are unworn.
The lower view shows the stoss side of a granite knob, also near Muir Glacier. Here the indications of abrasion are most conspicuous, but a groin crossing the foreground, and a niche at the right, are probably remnants of scars made by plucking.
The rock areas best showing the character of the sculp- ture due to plucking are in the barren regions about the glaciers, and these were often included in our views of glaciers; but the photographic methods employed to show details of the white ice do not secure the details of dark rocks. The peculiar embossment topography is merely suggested in some cases by the pattern which results from the preservation of snow in concavities of the surface. See the mountain spur beyond Reid Glacier in figure 14 and the hill at the left of Hugh Miller Glacier in plate m1. Similar patterns appear on both sides of Serpentine Glacier, in the photogravure at page 124 of volume I.
Figure 102 contrasts several types of sculpture. A tract bordering the water of the fiord at the right shows elab- orate fluting on a grand scale, the abrasive work of a powerful, and doubtless fast-moving, ice stream, flowing from left to right through the fiord. The material here sculptured is argillaceous slate, similar to that at Kadiak (figs. 86 and 87). The spurs beyond are partly of more obdurate material, including schists and granitoid rocks;
GLACIAL SCULPTURE 209
they were sculptured chiefly by currents approaching the fiord from the right; and plucking was an important fac- tor of the process. The peaks against the sky were above the Pleistocene ice.
In the last example the unevenness in the region of extensive plucking is partly due to the varying resistance of heterogeneous bed-rock. This factor finds strong ex- pression in the forelands and low islets at New Metlakatla, Sitka, and Kadiak, where peneplains well reduced toward base-level, and therefore presumptively of nearly even surface, were much roughened by a moderate amount of glacial deg- radation (see figs. 64, 65 and 86, and pl. xvi). =e"
It is also strongly ex- ~ pressed on the slopes of Unalaska Island about Unalaska Bay. There is a general lumpiness of the surface which would hao ail ONS throw doubt on the |i : it ones ua 2S Zs theory of extensive Pleis- Ae sai i. i tocene glaciation were the theory not strongly supported by the con- spicuous glacial sculp- ture of other parts of the island. Except where exposed in sea cliffs, the rocks are largely covered by a tundra mat, and this leaves room for doubt as to the steeper slopes, where many of the knobs may be landslips; but on the gentler slopes the knobs are clearly obdurate elements of the heterogeneous volcanic mass, rendered prominent by
WLAN 7, ivy Jf M { i a | h
Y Wy Y Wy
FIG. 102. ICE SCULPTURE IN RUSSELL FIORD.
210 ALASKA GLACIERS
differential erosion. A strip of lowland between Dutch Harbor and Iliuliuk is so hummocky and so set with lake- lets as to remind one of a terminal moraine of the Lauren- tide ice-sheet, and I half expected to find it a heap of glacial waste; but every discovered break in its turfy-mantle revealed volcanic rocks zz stu, and I was forced to regard its undulations as products of sculpture.
PRESSURE AND EROSIVE POWER OF TIDAL GLACIERS
The discussion, in the last chapter, of the fiords of the Alexander Archipelago assumes (page 163) that a tidal glacier is partly supported by the sea, so that the full weight of the ice does not press on the rock floor, and the glacier’s power to erode is correspondingly diminished. This assumption has been often made, and is usually given quantitative form. The sea is said to sustain a portion of the glacier equal in weight to the body of water displaced a by the ice, and correspondingly to dimin- ish the pressure of the glacier on its bed. WELLE When the subject is approached in a certain way this view seems altogether plausible. In figure 103, @ represents in
“iusilidméa Section a sea 2,000 feet deep with a flat == | bottom. In the sea floats an iceberg of which the sides are vertical and the top - and bottom are horizontal planes. Its one thickness is 1,600 feet, and the submerged part measures 1,400 feet, the densities of the ice and the water having the ratio of FIG. 103. DIAGRAMS 3 ‘ mivermatina vio. 7 108. The water sustams theooim TATION THEORY OF weight of the ice. Now conceive the Bapak GRACES: water of the sea to be drained away. The block of ice sinks to the bottom (4) and is wholly supported by it. Again, conceive the water of the sea to be only partly withdrawn, the depth being reduced from
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| | He
l
| | |
N
'
% VMdddiM bi UddiMdlddddee
PRESSURE OF TIDAL GLACIERS 211
2,000 feet to 1,400 feet (c). This is equivalent, so far as the block of ice is concerned, to raising the sea bottom from its position in @ until it touches the base of the ice- berg. The ice is not lifted by the sea bottom; it still pro- jects into the air just 200 feet; it is still supported by the water, and though touching the sea bottom does not press on it. Finally, conceive the water drawn down until its depth is but 7oo feet (d). This depth of water is just able to float a berg 800 feet thick. Therefore 800 feet of ice, or one-half the thickness of the block, are now sup- ported by the water, and the remaining 800 feet by the sea bottom.
Let us now approach the subject in a different way. Begin with a block of ice of the same dimensions as be- fore, resting on a horizontal bed, with which it is every- where in contact (fig. 104,@). The pressure on each square inch of the bed equals the weight of the column of ice above it—about 640 pounds. Now introduce sea water about the ice until it has a depth of, say, 700 feet (4). The water presses horizontally against the vertical faces (as indicated by the arrows), but, as there is no vertical ric. 104. pracrams component to a horizontal force, the water 'tUSTRATING NoN-
+ . ° FLOTATION THEORY pressure neither lifts the ice block nor 4. rar ctactes. pushes it down. The block continues to rest on the bed, exerting still a downward pressure of 640 pounds per square inch of base. ‘This line of reason- ing seems quite as plausible as the other, but the result is different.
A little consideration discovers the cause of the dis- crepancy. In the first analysis it is tacitly assumed that the water exerts its pressure not only on the sides of the ice block but on its base, and this whether the block floats free or touches the sea bed. In the second analysis it is
212 ALASKA GLACIERS
tacitly assumed that the contact of the ice with the bed excludes the water. In order to determine which analy- sis is applicable to the case of the tidal glacier, it is neces- sary to consider whether the nature of the contact between the glacier and its bed is or is not such as to exclude the sea water and its pressure.
It was suggested by my colleague G. F. Becker that a laboratory test might be applied to one of the principles appealed to in the second of the two analyses — the prin- ciple that a solid rectangular block immersed in a liquid is not buoyed up by the liquid provided its base is in com- plete contact with the bed on which the liquid rests; and at his request two pertinent experiments were made by A. L. Day in the physical laboratory of the U. S. Geolog- ical Survey. In the first experiment a small slab of plate glass was cemented to the bottom of a glass vessel (fig. 105 ), for the purpose of giving an accurately plane surface, and the vessel was then partly filled with mercury. A second piece of Z plate glass was immersed in the
_-=Z mercury and pushed down until {ii + one of its faces came into contact Fic. 105. conracr ramxom- With the face of the fixed slab. Ag ENA OF GLASS AND MER- the density of mercury is about five
CURY. ° A block of glass rests ‘on ihe bot- times that of glass, some force was tom; asimilar block floats needed to immerse the block of
at the surface. glass, but as soon as contact had been secured with the slab below, the block remained at the bottom. Not only did it show no tendency to rise, but force was necessary to detach it. As both glass sur- faces had been carefully cleaned, there could be no cemen- tation; the phenomenon was one of hydrostatic pressure, conditioned by the contact relations of glass with mer-: cury. In the second experiment water was substituted for
PRESSURE OF TIDAL GLACIERS 213
mercury; and, as glass is heavier than water, the glass block was replaced by a block of cork, to the bottom of which a thin plate of glass was cemented. When the cork was pushed down through the water and its glass face squeezed against the slab of glass at the bottom, it was found to adhere, but not permanently. The pressure ap- plied did not force all the water from between the glass faces, and the remaining water film gradually thickened, until, in a few seconds or a few minutes, the cork was freed and rose to the surface.
As regards conditions, the only essential difference be- tween the two experiments was in the liquids employed, and the properties of the liquids which determined the diverse results were the relations of internal to external molecular forces. Because the cohesive force of water is less strong than its force of adhesion to glass, water ‘ wets’ a glass surface; it is able to spread and interpose itself as a film between two glass surfaces pressed tightly to- gether; and when thus interposed it can not be forced out by pressure (at least, by such pressure as is involved in the problem of the tidal glacier). Because the cohe- sion of mercury is stronger than its adhesion to glass, it does not wet glass; and it does not tend to insinuate itself between closely approximated glass plates, but tends rather to withdraw from the interspace.
These experiments indicate that the ability of the sea to penetrate, and communicate its pressure, along the contact surfaces of a tidal glacier and its bed, may depend on the cohesive force of water, as compared with its ad- hesive force in relation to ice and rock. It is a familiar fact that water wets both ice and rock; and the problem of the glacier is therefore better represented by the second of Day’s experiments than by the first.
Another factor of the problem should now be consid- ered, the temperature of the bottom ice and adjacent rock;
214 ALASKA GLACIERS
for if these fall below the freezing temperature, a film of water can not exist between them. This is a subject which has received considerable attention, and although direct observation is impossible, there seems a good foundation for inference. By the aid of crevasses and borings it has been found that the upper ice (outside the névé region) has at all times a temperature of almost ex- actly 32°, seasonal and diurnal variation being confined to a very thin surface layer. The upper ice therefore has no cooling effect on the bottom ice. On the other hand, the bottom ice receives heat in three ways: Heat comes to it by conduction from the interior of the earth; heat is developed by the friction of ice and waste on the bed- rock; and the internal work of the flow of the ice devel- ops heat, of which a part is conducted downward. The bottom ice therefore maintains a temperature of 32° (more precisely, the freezing temperature corresponding to the pressure), and the adjacent rock is slightly warmer. There is a continual, though very slow, melting of the basal ice, and a film of water is maintained between it and the rock. It is probable that the streams of water which flow from glaciers all through the winter are sup- plied chiefly by basal melting; and we may further sup- pose that the tunnels through which those streams flow are connected with the thin water film by a graduated and ramifying system of minor passages. The ways which serve for the escape of the product of basal melting serve also, in the case of tidal glaciers, for the communi- cation of the hydrostatic pressure of the sea water. Statically considered, the film of water under the gla- cier is subject to a group of forces in equilibrium. The weight of the glacier presses on it and tends to expel it. This is resisted by the molecular forces associated with the contact faces of the film, and by the hydrostatic pres- sure of the sea water outside. As the film is added to by
PRESSURE OF TIDAL GLACIERS 215
melting, and as the added water must escape by flow, there is also a dynamic factor, the viscous resistance to flow. These forces conjointly determine the thickness of the film. The film is thicker as the ice column is less, as the sea-water column is greater, and as the melting is more rapid. It is always very thin.
We may now advantageously return to the question of the mode of support of the tidal glacier. Referring to the diagram (fig. 106), it is evident that the ice receives no support from the pressure of the sea water against its frontal cliff. It rests wholly on the film of water beneath it, and its pressure is communicated by the film, without loss, to the rock QZ beneath. The film is not a mere con-_ ric. 106. eat sxc- duit, communicating the static pres- 710N OF TIDAD GhACIES:
° Showing relation of the sure of the sea water. If it were, the sea to the subglacial water- ice would not be supported, because fiw is cuormucly exaggen that pressure is less than the down- *¢ ward pressure of the ice. In virtue of the molecular forces brought into play along the contact planes, the film has some of the properties of a solid. It is, in some sense, an elastic spring or cushion interposed between the ice and the rock. It performs its function of transmitting the pressure of the glacier to the rock bed quite indepen- dently of the presence of the sea. The pressure of the sea water modifies the infinitesimal thickness of the film, but does not prevent the rock bed from supporting (through the mediation of the film) the whole weight of the glacier.
The last statement is subject to a single qualification. Wherever the feeble flow of water from basal melting maintains passages of more than capillary size, the molec- ular forces locally cease to dominate, and the hydrostatic pressure of the sea water contributes support to the glacier. To this extent, which must always be relatively
216 ALASKA GLACIERS
very small, the pressure of a tidal glacier on its bed is diminished by the sea.
It thus appears that there is no important difference, as respects pressure on the rock bed, between a glacier rest- ing on the land and one which is partly bathed by the water of a fiord; and, so far as glacial erosion is con- ditioned by pressure, the presence of the sea does not diminish the efficiency of the glacier. It is possible, how- ever, that the rate of erosion is affected by changes in the thickness of the capillary film of water. In the familiar case of the grindstone, the application of water modifies abrasion in two ways: It acts as a lubricant to diminish friction and reduce the efficiency of the stone; and it acts as a carrier to remove the product of abrasion, prevent clogging, and thus enhance the efficiency. The sub- glacial film doubtless has both these functions, and both should be affected by its thickness; but as the two are antagonistic in relation to abrasion, it is not at once evident whether a thickening of the film should increase or diminish the erosive work of the glacier.
It seems furthermore possible that the influence of film thickness on abrasion may not be the same for waste par- ticles of all sizes. It may be important with reference to the finest rock flour, where the diameters are of the same order of magnitude as the depth of the film, and quite un- important with reference to the work of sand and still coarser waste. And if we turn from abrasion to plucking, we seem to pass altogether out of the field of influence of the subglacial film.
While it is not altogether easy to picture the combina- tion of molar and molecular forces associated with the sub- glacial film, and while it is still more difficult to analyze the eftect of variation in that film on so complicated a proc- ess as glacial erosion, I am nevertheless confident that the influence of the sea in diminishing the pressure of a
PRESSURE OF TIDAL GLACIERS 217
tidal glacier has been greatly overrated, and I discredit the supposed power of sea pressure to make important reduction of a glacier’s efficiency for erosion.
The preceding pages were submitted in manuscript to several friends competent to consider questions in molec- ular physics. Some of them think the ability of the sub- glacial film to resist expulsion has been overestimated, and especially that the film should not be assumed to exist between the bed-rock and the abrading angles of rock particles held in the ice. If it be true that abrading par- ticles are in absolute contact with the bed, and if it be further true that there is no film between the same particles and the partly enveloping ice, then parts of the glacier (regarded as a body of ice and fragmental rock) are directly supported by the bed. However important the distinction may be with reference to a complete theory of glacial abrasion, it seems to have little bearing on the question of pressure as here considered. We may conceive the whole glacier to consist of infinitesimal vertical columns, some terminating on the bed and sup- ported by it, others resting directly on a capillary film of water and thus indirectly supported by the bed, and yet others terminating on a water stratum of supercapillary depth. The last are sustained in part only by the hydro- static pressure communicated by the water stratum, and are otherwise upheld directly by their coherent neighbors of the first and second groups, and through then, indi- rectly, by the bed.
It is a corollary to the general conclusion of this section that the existence of a fiord — that is, of a glacial trough partly occupied by an arm of the sea— is not demonstra- tive of a relatively low base-level at the time of its excava- tion. In the regions of the Alexander Archipelago and Prince William Sound there is independent reason to think the base-level was relatively low when the glaciers
218 ALASKA GLACIERS
were largest, but the case is not strengthened by the pres- ence of the sea in the glacier channels.
RIVERS OF ICE AND OF WATER
The resemblance which glaciers of the alpine type bear to streams of water, has impressed all observers, and it includes so many details of form and work that the phrase ‘river of ice’ seems more than a mere figure of speech. The fact that resemblances arrest attention, of course im- plies that there are also differences; the contrast between the two materials, ice and water, is so extreme that cor- respondences in their behavior are unexpected and there- fore striking. If we disregard this fundamental difference in material and restrict attention to other causes controlling the phenomena, then we may say that some of the re- semblances between glaciers and rivers are of the nature of homologies, in that the causes of the corresponding features are like, and other resemblances are of the nature of analogies, in that the causes are unlike. Before attempt- ing a classification of resemblances on these lines, I shall enumerate the features of alpine glaciers which have been regarded, or which seem worthy of regard, as correspond- ing to similar features of rivers.
Resemblances.—(1) Upland precipitation is gathered
into streams which flow down the slopes. (2) As they
flow they meet and join together, forming greater streams, which follow the main valleys or gorges. (3) Sometimes a stream parts against a prominence and reunites beyond it, thus surrounding an island (nunatak); (4) sometimes the parted members proceed independently, as distribu- taries. (5) All parts of the stream are subject to gain and loss of material. In an upper division gain is in excess; in a lower division, loss. In complete examples the maximum volume is in mid-course, and the stream ends distally by complete dissipation. (6) If the stream
a ——<—_ L e
GLACIERS AND RIVERS COMPARED 219
reaches the sea it is cut off, and its history of volume- change ends abruptly.
The velocity of flow is greater (7) in the middle of the stream than at the sides, (8) at the top than at the bottom, (9) on the outer side of a bend than on the inner, (10) where the channel is narrow than where it is broad, (11) where the grade is high than where it is low, (12) ina large stream than in a small.
(13) The surface of the stream, considered as to its major features, is smoother than the channel bed. (14) It is exceptionally high on the upstream side of an island, and exceptionally low on the downstream side. (15) It is roughened in detail by concealed prominences of the bot- tom, especially where the stream is shallow. (16) The surface descends normally in the direction of flow, but exceptionally, and for short distances, ascends.
(17) The stream erodes its bed and the walls of its channel. (18) The chief tools of erosion are rock frag- ments carried by the stream. (19) The greater the velocity of the stream the more rapid the erosion (except, perhaps, in cirques). (20) The stream shapes its chan- nel, making the width several times greater than the depth. (21) The fully adjusted channel is broader in yielding material than in obdurate; but has uniform width in uniform material. (22) The contours of the adjusted channel are smooth curves of large radius. (23) The adjusted channels of large streams are broader and deeper than those of small streams. Where a large stream is joined by a small tributary and the surfaces of the two have the same level, the bed of the large stream lies lower than that of the small. (24) The erosion of the channel in gorges saps the cliff walls, causing coarse waste to fall to the stream. (25) The waste from erosion and sapping is carried forward by the stream and eventually deposited.
(26) Where a heavily loaded stream issues from a moun-
220 ALASKA GLACIERS
tain gorge to an open valley, it sometimes deposits waste at the sides and beneath until it comes to flow in a walled causeway, or raised trough, of its own construction. It may then overflow a wall of the trough and assume a new course." :
Differences.— The features of difference are equally noteworthy. The speed of the glacier is very much slower than that of the river, being better expressed in feet per year than in feet per second. The rates of wax- ing and waning are correspondingly slow. A river flood is propagated downstream by the actual transfer of the water added about the upper course; a glacier flood is believed to be propagated downstream as a wave travel- ing more rapidly than the ice. The depth and width of a glacier are much larger, in relation to length, than those of a river. The threads of flow in a glacier run nearly parallel; in a river they weave freely in and out. That which falls to the back of a glacier, though much denser than the ice, does not sink to the bottom, but is carried for- ward as a back-load; only light materials float on a river. Most of the waste embedded in a glacier is moved along continuously; most of the waste constituting the load of a river is transported intermittently, being repeatedly picked up and laid down.
Homologies and Analogies.—The gathering of ice into streams and its downward flow are caused by gravity, just as inthe case of water. Most of the inequalities of veloc- ity are determined by gravity in conjunction with the fric- tion of the ice on the channel and the resistance of ice to internal shear; and the processes are essentially the same as with water. But the greater velocity on the outside of a bend involves an analogy only. The bending stream of ice distributes the velocities of its elements in such
1]. C. Russell. Eighth Ann. Rept. U.S. Geol. Survey, part 1, pp. 337-342, 360-366, 1889.
GLACIERS AND RIVERS COMPARED 221
way that the total work of channel friction and internal shear is a minimum, and that distribution throws the locus of maximum velocity to the outer side of the middle of the stream, but the general relations of the parts of the stream are not changed. The preservation of the general rela- tions is clearly shown by medial moraines, which map out surficial lines of flow. Inthe bending river, momentum is the controlling factor. Those fillets of the stream which above the bend moved fastest are thrown to the outer side of the curve, and the slower-moving fillets are crowded to the inner side. Usually the upper water moves to the outside of the bend and the lower water to the inside, so that there is a torsion of the body of water as a whole.
The correspondences connected with gain and loss of material are close, and the parallelism can be traced through many details, but the processes are so different that the similarities of result can not be classed as homol- ogies. Alimentation of the glacier is primarily through snowfall, secondarily through rainfall, and there is storage in snow banks that subsequently descend as avalanches. Alimentation of the river is primarily through rainfall, secondarily through the melting of snow and ice, and there is storage in ground water that slowly issues in springs. Dissipation of the glacier is chiefly by melting and secondarily by evaporation. Dissipation of the river is wholly by evaporation, but part of its evaporation is preceded by absorption by the ground.
The general evenness of the stream surface is deter- mined in each case by gravity, and so is its descent in the direction of flow; but the exceptional ascent in the direc- tion of flow has diverse causes. Where the passage of an ice stream over an embossment of its bed is expressed by a local rising of its surface, the imperfect adjustment of the surface is a result of viscosity; the upward slope of water under similar circumstances is a result of impetus
222 ALASKA GLACIERS
or momentum. So, too, the roughening of the glacier surface where the flow is disturbed, by breaking into seracs and pinnacles, is analogous to, rather than homol- ogous with, the breaking of a river surface into waves. Viscosity causes the rupture of the ice, momentum the undulation of the water. The deflection of the viscous ice produces stresses and strains, some of which are ten- sile; in the depths of the stream the tensile stresses are balanced by compressive stresses due to the weight of overlying ice, but higher up the ice is overstrained and ruptured. When the swift-flowing water rises over an obstruction its momentum causes a portion to shoot above the normal level, and thus starts an undulation.
The causes of the relation of channel depth to channel width are not sufficiently understood in the case of glaciers to warrant a comparison with rivers. The disparity of channel depth at the mouth of a small, fully-adjusted trib- utary is in each case a phenomenon of base-level con- trol. The surface level of the tributary is determined by the main stream, and if the tributary at any time erodes its channel rapidly, its stream becomes deeper, its velocity less, its power to erode less, and thus the tendency to deepen is limited. The resemblance of glaciers to rivers in this respect is a homology.
The adjustment of channel contours to simple curves is brought about, in both classes of streams, by the more rapid erosion of projecting angles, but the work of the water is concentrated on these through the property of momentum, and the work of the ice through viscosity.
The walled causeways sometimes built by streams of ice debouching onto a plain have a different process of construction from the similar causeways occasionally built by streams of water. The walls of the glacial causeway are made by the deposition of lateral moraines that had been carried chiefly as back-load. The walls of the fluvial
VISCOSITY AND MOMENTUM 223
causeway are made by the deposition of suspended waste through the slackening of spreading side currents.
The salient fact brought out by these comparisons is that many features of rivers and river work which arise from inertia in association with swift motion are paralleled by features of glaciers and glacier work which arise from high viscosity in association with slow motion. In each kind of stream, changes in the direction of flow are caused by irregularities of the channel, and complex series of phenomena arise from the resistance of the current to deflection. These series are strikingly parallel, but the resistance to deflection is occasioned in one case by momentum and in the other by viscosity.
INDEX
Abercrombie, Captain W. R., map 72 Acknowledgments, assistance by col- leagues 10 photographic material 5 Alexander Archipelago, depth of fiords 134 fiords 150-159 pre-glacial topography 130 Amherst Glacier 82, 82 (pl.) Annette Island 130
Baranof Cape 132, 132 (pl.) Barry Glacier 90-93 Base-level, pre-glacial 134 Base-level plains. See Peneplains. Base-levels, Pleistocene 162-166, 172, 184 Becker, G. F., cited on glacial erosion 204 cited on statics of tidal glacier 212 Behm Canal 128, 134, 140, 159 Bendeleben Mountains 193 Bering Sea 186-194 Berner Bay 127, 140 Biological Survey, U. S., acknowledg- ments v Alaska photographs 5, 6 photograph of Wellesley Glacier 88
photograph of Yale Glacier 83 Bonney, T. G., cited on hanging val- leys 114 Boundary Commission. See Canadian International Boundary Commission. Brabazon, A. J., photographs 27, 28, 29, 38
Brady Glacier 45, 106, 123
British Columbia, glaciation of coastal region 141-150
Brooks, A. H., geology of Seward Peninsula 192
Bryn Mawr Glacier, frontispiece, 87, 88, 175
Canadian International Boundary Commission, acknowledgments v maps and photographs about Gla- cier Bay 16, 25, 26, 28, 29, 38 maps and photographs about Lynn Canal 12, 13, 15 maps and photographs about Ya- kutat Bay 46, 62, 65, 67, 209 photograph series 6, 122 photographs of fiords 158 photographs of upland topography 123, 125, 127, 128, 140 Cape Baranof 132, 132 (pl.) Cape Spencer peneplain 123-126, 141 Cataract Glacier 94 Cascading glacier, Nunatak Fiord 61 glaciers, College Fiord 89, 175 Caves in Barry Glacier 91 Chamberlin, T. C., cited on hanging valleys 114 Charpentier Glacier 34-37 Chatham Strait 134, 151-155 Chatham Strait Glacier 162 Chilkat Inlet 13, 15 Chilkoot Lake 141, 154 Chiniak Bay 179 Cirques 141 Clarence Strait 134
( 225 )
226 INDEX
Coast Survey, U. S., maps 12, 15, 26, 49; 50, I19 photographs 122, 187 soundings 158 College Fiord, existing glaciers 81-89 map 8o (pl.) Pleistocene glaciation 175-176 Collier, A. J., cited on geology of Seward Peninsula 192 Columbia Bay 73, 81, 174 Columbia Glacier 70 (pl.), 71-81, 104 surface features 200 Columbia River 137 Coville, F. V., acknowledgments 10 observation of young spruces 78 visit to Columbia Glacier 71 Crescent Glacier 82, 82 (pl.) Crevasse cycle 198-203 Curtis, E. S., official series of views 5 photographs of glaciers 6, 74 (pl.), 86, 88, 94, 94 (pl), 95 photographs of Wrangell and Sitka 132 (pl.) Cushing, H. P., geologic studies in Glacier Bay 16, 17
Dall, W. H., acknowledgments 10 cited on Kadiak terraces 179 cited on Pleistocene glaciation 187 observations of Grewingk Glacier 98, 100 Pleistocene shells 165 Dana, J. D., cited on glacial erosion by plucking 207 Davidson Glacier 12-16, 105, 157 compared with glacier of Russell Fiord 51 compared with Pleistocene glaciers of Fairweather Range 169 Davis, W. M., cited on hanging val- leys 114 Dawson, G. M., Alexander Archipelago 141 cited on ancient glaciers of Van- couver Island region 145 cited on geology of coast ranges 129 Day, A. L., experiments 212 Denudation. See Erosion.
Discovery Passage 143 Disenchantment Bay 46-49, 62 (pl.), 63-70, 104
Doran Strait 90
Disenchantment Bay Glacier 49
Douglas Island 132, 165
Drift 35, 161 , influence on topography of glaciers
202 Dutch Harbor 185, 210
Earthquake 23 Emerson, B. K., acknowledgments 10 Erosion, by glaciers and rivers com- pared 218-223 by Pleistocene glaciers 139-163 by tidal glaciers 210-217 fiord 162 principles of glacial 203-210 Estuaries, coast of Washington 137
Fairweather Range 39, 123, 125, 126 existing glaciers 148-150 La Perouse Glacier 39-45 Pleistocene glaciation 166-170 variations of glaciers 105, 107
Fiord erosion 162
Fiords, Inside Passage 141-150 strike 125, 142-157 transverse 142, 157-159
Fiords and islands 119-122
Fish Commission, U. S., photographs
44, 65, 67 Fort Wrangell 132 (pl.) Fraser Reach, hanging valleys 145-147.
Gannett, Henry, acknowledgments 10 cited on cascading glaciers 175 cited on hanging valleys 114 map of Alaska 1 (pl.) map of Disenchantment Bay
62 (pl.), 65 map of Hidden Glacier 52 (pl.) map of Muir Inlet 21 map of Nunatak Glacier 58 (pl.), 62 map of Port Wells 80 (pl. ), 81 route 4 Garwood, E. J., cited on hanging val- leys 114
INDEX
Gastineau Channel 132, 165 Geikie Glacier 38 Geikie Inlet 38 Geological Survey, U. S., acknowledg- ments v photographs by 5, 6 Georgia, Gulf of 134 Glacial deposits 161 Glaciated rocks 206 (pl.) Glaciation, Pleistocene 113-194 Glacier, Amherst 82, 82 (pl.) Barry 90-93 Brady 45, 106, 123 Bryn Mawr frontispiece, 87, 88, 175 Cataract 94 Charpentier 34-37 Chatham Strait 162 Columbia 70 (pl.), 71-81, 104, 200 Crescent 82, 82 (pl.) Davidson 12-16, 51, 105, 157, 169 Disenchantment Bay 49 Geikie 38 Grand Pacific 26-33 Grewingk 97-102, 104 Harriman 94, 94 (pl.) Harvard 82, 84 Hidden 47, 52 (pl.), 52-58, 202 Hubbard 47-49, 62 (pl.), 63-70, 196 Hugh Miller 34, 35-38 Johns Hopkins 27, 28, 32, 106 La Perouse 39-45, 104, 167 Malaspina 46, 49, 106 Muir 20-25, 198, 199 Nunatak 47, 58 (pl.), 58-63 Puget Sound 135, 139 Queen Charlotte Sound 145 Radcliffe, 84-87, 175 Reid 27, 28-32 Roaring 96 Serpentine 93 Smith 86, 87, 175 Strait of Georgia 145 Surprise 94 Turner 47, 62 (pl.), 64, 66 (pl.), 66-69 Vassar 88, 175 Wellesley 175
2247
Glacier, Wood 38 Yale 82, 83 Glacier Bay 16-39 variations of glaciers 103 Glaciers, annual cycle 22 basal melting 214 cascading 61, 89, 175 causes of variations 102-112 classification 10 College Fiord 81-89, 175-176 comparison with rivers 218-223 dates of photographs 5 existing 7-112 general distribution 7-9 Glacier Bay 20-39 hanging I1, 114-119 Lynn Canal 11-16, 126, 134, 150- 157 piedmont 10 Pleistocene 113-194 Port Wells 81 pressure and erosive power in fiords 210-217 principles of erosion and sculpture 203-210 relation to forests 41-44, 45, 49, 51, 52, 76, 78-80, 88, 92, 95, 96, 98, IOI, 106 sculpture by Pleistocene 139-163 summary of modern changes 102- 106 surface characters 196-203 tidal 11, 210-218 Glenn and Abercrombie, map 72 Graham Island 165 Grand Pacific Glacier 26-33 Gray Harbor 137 Grenville Channel 146 Grewingk Glacier 97-102, 104 Gulf coast, summary of Pleistocene geology 182-185 Gulf of Georgia 134
Haenke Island, contact with Hubbard Glacier 48, 70 photographs 65, 67 position 47, 50 Hall Island 188 Hanging glaciers 11, 114-119
228 INDEX
Hanging glaciers, in Harriman Fiord 93, 94, 95, 176. See also Hanging Valleys. Hanging valley, Kadiak Island 181 Plover Bay 191 Princess Royal Island 116 (pl.) Hanging valleys 114-119 Inside Passage 142-150 Lynn Canal 153, 154 Nunatak Fiord 60, 61 Yakutat Bay 170 Harriman, E. H., photograph by 95 Harriman Fiord 80 (pl.), 89-97 Pleistocene glaciation 176 Harriman Glacier 94, 94 (pl.) Harvard Glacier 82, 84 Hayes, C. W., cited on height of névé line 8 Hecate Strait 134 Hidden Glacier 47, 52-58, 52 (pl.), 202 High mountain district 166-173 Hinchinbrook Island 174 Hubbard, Gardiner G. 63 Hubbard Glacier 47-49, 62 (pl.), 63- 70, 106 Hugh Miller Glacier 34, 35-38 Hugh Miller Inlet 34-38
Ice. See Glacter and Viscosity. Iceberg waves 31, 69 Icebergs, Muir Inlet 24 Reid Inlet 33 Iliuliuk 186, 210 Inertia of rivers compared with vis- cosity of glaciers 223 Inland Passage district 119-166 Inside Passage 121, 142-150 Inverarity, D. G., photographs by 62, 92, 94 (pl.) Island, Annette 130 Douglas 132, 165 Graham 165 Haenke 47, 48, 50, 65, 67, 70 Hall 188 Hinchinbrook 174 Kadiak 177-182, 189 Montague 176
Osier 47, 65, 69 Pitt 146
Island, Princess Royal 116 (pl.), 145, 146 St. Matthew 188, 193 St. Paul 187 Unalaska 185 Vancouver 143-146, 165 Islands, Queen Charlotte 165 Islands and fiords 119-122 Itinerary 3
Johns Hopkins Glacier 27, 28, 32, 106 Johnstone Strait 143
Kadiak Island 177-182, 189
Kenai Peninsula 97, 177
Kerr, M. B. 1
Kettle-holes, near Grewingk Glacier
100 near Hidden Glacier 54 (pl.), 54- 56 Kigluaik Mountains 192 Klotz, Otto J., cited on variations of glaciers 45, 103
La Perouse, J. F. de G., exploration of Lituya Bay 45 observations of Disenchantment Bay Glacier 51 La Perouse Glacier 39-45, 104, 167 La Perouse Peak 123 Lituya Bay 149, 150, 167 Lowe Inlet 148 Lynn Canal, configuration of bottom 134 glaciers 11-16 origin of 150-157 upland topography near 126
McArthur, J. J., photograph by 13 Malaspina, A., visit to Disenchant- ment Bay 48 Malaspina Glacier 46, 49, 106 Map of Alaska, showing route 1 (pl.) Mendenhall, W. C., cited on glaciation of Alaska Peninsula 192 Merriam, C. Hart, photographs by 5, 6 photograph of Amherst Glacier 82, 82 (pl.) preface v Montague Island 176 Moraine, section 56 (pl.)
ae
ee. ee ee
INDEX
Moraine-building at sea front 163-165, 168-170 Moraine delta, Davidson Glacier 13-16 Grewingk Glacier 97 Hidden Glacier 52-57 Muir Glacier 19 Moraines, base of Fairweather Range 166-170 near Yakutat Bay 171 overridden by Columbia Glacier 77 under Yakutat Bay 49-51 Moraines, push-, Columbia Glacier 76-80 Grewingk Glacier 100 La Perouse Glacier 42 Muir, John, acknowledgments 10 cited on Hugh Miller Glacier 35 cited on Pleistocene glaciation of Bering Sea region 186 exploration of Glacier Bay 16, 17 route in 1899 3, 4 studies of Brady Glacier 45 studies of Geikie Inlet 38 studies of Grand. Pacific Glacier 26, 29, 32 studies of Muir Glacier 21 visit to Harriman Fiord 81 Muir Glacier 20-25 limit of crevasses 198 seracs 199 Muir Inlet, glacial erosion 207 ice pack 24 map 21
Nanaimo 165
Nordenskiold, A. E., cited on glacia- tion of Siberia and Alaska 187, 192
Nunatak Fiord 46, 58, 61, 62
Nunatak Glacier 47, 58 (pl.), 58-63
Ocean Cape 170
Ogilvie W., photograph of Davidson Glacier 12
Orca 174
Osier Island 47 ice-fall waves 69 photographs 65
Palache, Charles, acknowledgments 10
229 Palache, at Columbia Glacier 71 route 3, 4 Penck, A., cited on hanging valleys 114 Peneplains, high, Kadiak Island 177, 183
Kenai Peninsula 177, 183 Prince William Sound 172, 183 southeastern Alaska 123-130, 183 Peneplains, low, Alexander Archi- pelago 130-134, 159, 183 glaciation of 209 Kadiak Island 179, 180, 182, 183 Photographs of glaciers 4 Pitt Island 146 Pleistocene glaciation 113-194 Plover Bay 190 Plucking 203, 205, 207-209 Port Clarence 188 Portland Canal 134, 159 Port Wells 80 (pl.) existing glaciers 81-97, 104 Pleistocene glaciation 175 Pre-Pleistocene topography 122-139 Pressure of tidal glaciers 210-217 Prince William Sound, ancient base- levels 172 existing glaciers 71-97 map 80 (pl.) Pleistocene glaciation 173-176 Princess Royal Island, hanging valleys 116 (pl.), 145, 146 Puget Sound 135 Puget Sound Glacier 135, 139 Push-moraines, Columbia Glacier 76- 80 Grewingk Glacier 100 La Perouse Glacier 42
Queen Charlotte Islands 165 Queen Charlotte Sound 134 Queen Charlotte Sound Glacier 145
Rabot, Charles, cited on cause of gla- cial variation 106 Radcliffe Glacier 84-87, 175 Reid, H. F., cited on cause of glacial variation 109 cited on variations of glaciers 103 nomenclature of glaciers 11
230 INDEX
Reid, H. F., studies of Muir Glacier at, 23 survey of Glacier Bay 1, 16, 17, 25, 26, 28, 29, 38 Reid Glacier 27, 28-32 Reid Inlet 25-34 Rivers of ice and water compared 218- 223 Roaring Glacier 96 Rock table 201 Route, map of 1 (pl.) of author 3 of Expedition 1, 2,3 Russell, I. C., cited on buried forest 52 cited on Disenchantment Bay and Russell Fiord 48 cited on glaciation of Unalaska Island 185 cited on Hidden Glacier 56 cited on marine shells 173 cited on nomenclature 11 cited on Nunatak Glacier 62 cited on variations of glaciers 103 classification of glaciers 10 Davidson Glacier 13 photograph of Hubbard Glacier 65 photograph of Turner Glacier 66, 66 (pl.) studies in Glacier Bay 16, 17 survey of Malaspina Glacier 1, 46 Russell Fiord 46, 47, 51-63, 69 types of glacial erosion 208
St. Elias Alps 166 height of névé line 8 recent uplift 173 St. Matthew Island 188, 193 St. Paul Island 187 Sea-levels, Pleistocene 162-166, 172 Seracs 198 Serpentine Glacier 93 Seward Peninsula 192 Shaler, N. S., cited on pressure melt- ing 204 Shells, Pleistocene 165 Siberia 190, 193 Sitka 131, 132 (pl.) Smith Glacier 86, 87, 175 Speel River 158
Spencer Cape, peneplain 123-126, t41
Spurr, J. E., cited on terraces of Un- alaska Island 186
Stevens Passage 134
Strait of Georgia 134
Strait of Georgia Glacier 145
Streams of ice and water compared 218-223
Surprise Glacier 94
Terrace, Annette Island 130 near La Perouse Glacier 167 Seward Peninsula 193 Spruce Island 179 Terraces, Prince William Sound 176 Unalaska Bay 186 Yakutat Bay 170 Tidal glaciers 11 Tidal glaciers competent to erode 210- 217 Tittmann, O. H., ice pack in Muir In- let 24 Tracy Arm 159 Turner Glacier 47, 62 (pl.), 64, 66 (pl.), 66-69
Unalaska Bay, glaciation of 209 Unalaska Island 185 U. S. Biological Survey, acknowledg- ments iii Alaska photographs 5, 6 photograph of Wellesley Glacier 88 photograph of Yale Glacier 83 U.S. Coast Survey, maps 12, 15, 26, 49, 50, 119 photographs 122, 187 soundings 158 U.S. Fish Commission, photographs 44, 65, 67 U.S. Geological Survey, acknowledg- ments v photographs by 5, 6 Uyak Bay 178
Vancouver, George, cited on Columbia Glacier 71 map of Columbia Bay 71, 80 observations in Disenchantment Bay 48 observations in Glacier Bay 17
— -
INDEX
Vancouver, George, observation of Brady Glacier 45 Vancouver Island, hanging valleys 143-146 marine clays 165 Variations of glaciers 102-112 Vassar Glacier 88, 175 Viscosity of ice, compared with inertia of rivers 223 in relation to glacial erosion 204
Walker Bay 128 Waste plain, Davidson Glacier, 13- 16 Grewingk Glacier 97 Hidden Glacier 52-57 Wellesley Glacier 175
231
Whidby, Joseph, cited on Columbia Glacier 71
Willapa Bay 137 Willis, Bailey, cited on Puget Sound Glacier 135 Wood Glacier 38 Wrangell 132 (pl.) Wright, G. F., studies in Glacier Bay 16, 17, 21
Yakutat Bay, submerged moraines 49- 51 terraces 170 Yukutat Bay region 45-70 Yakutat village 170 Yale Glacier 82, 83 York Mountains 193
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