t, ..

_3 l tc.

DOCUMENT CONTROL

The Exceptional Advances of the :Muldtl'W, Black Rapitla, and Susltna Glaclfn's

AusTIN S. PosT

7816 Champagrns Pvint llond, Kirklt:mdt Waahmgto1a

Abstract. Muldr~w Olp.cier in Alaaka adv!U\ced extremely ·mpidly during the winter oi 1056-1957, with surface movemtnU! of ire Amounting to over .,.6 km. Th~ flow wua ~~­panied by a. pronoun~d lowering of the aurfa,a, of the upper portion of the glAcier by no m, or more, with a. correaponding ri!!e in tsurface ice level! in the terminal pgrtion; tlut net ox· ~of it'e ia roughly computed to be e{j,ual. No other giacier in the region .mowed evidel'loo o£ A llimilar movemnnt during the I'J!Ulle ~riod. However, the Black P..apid.t! GlAcier in 1931, the YAJ:Jert in 1942, and the Suaitna in 1953 did make ~tdva.nces o! a similar nature. Un\ll!U.U medial moraine>l indie~te that at least tuo of these gt~Wiern have previously alterUAted between stagnation and sudden, b;iet movemen\.3. No evidence waa found to iruggest short-term climatic ·~~tulilious ftt.\nrnhte t'l large s11ow IH"{'umulation on thf.>se glaciers prior to their ndvn...n~. Correlation ootween }Qt.~l e&rthquakea and these i~ move'!lenta is also lacking. Evidence dOOii indio:lte that th~ t!.dvimcee re~ul.t from critical dynamic conditiomt met with in oort.&ih glacier aysteiN ia.vonna long periods of stagnation followed by sudden: displacements of ice.

I NTRODUC"i'ION

ln the wmtcr o£ 1900-!957, the Muldrow Gla­cier, after many y~:.ars of quiescence and slow retreat, eudd"nly snd. unexpcetediy made a. spec­taeulu M1Jafice

1 with i~ movem.enro down the

sJacier amounting to 6.6 km ( 4.1 mi) taking plae~;> m a. few months. A similat short-lived movement v."M witnessed m the Black Rapids Glacier in 1936-1937, and in 1952 or 1953 the Susitna Glo.­cicr made a like movement.

Thtae adv:: "'es npparcntly nre not a nonnn.l ~n to climu.tic changes and may J.avt> sig­n.i1icanee to our understanding of the mechan~ ism of ~t.cier fie';;'.

All th~ gl~ers o.re l<Jcated in the Alaska. F~nge in c:entral Alaslm. Among the many glaciers present, thooa described in this report are conspicuous only because of there lmown advances and unusual surface ft>aluft's displayed.

MULDitOW GLACIER

This glacier is lo~tcd on the northern slope of the AlbEka Range m Mt. MrKiniey National Park. Headir:g in the summit r.no\"1"8 of Mt. Me~ Kinley, 6193 m (20,320 £t) 1 North Ameriea's highest penk, the glacier, at.Qut f;3 km {39 mil in kmgth. desoonds abruptly to zm elevation ·of aoout 2(n) m (()600 it"J ~ thf'n mor~ lll"llCHall:'o'· to its terminus at 762 m {2500 ftJ. It is jt)ined by its ~t tributAry, tbe '!"rcleika, at .an dc'laU()n

of 1737 m (5700 ft) and by another major lmmch, tnu Brooks Glru;ier, at an elevation of 1646 m (5400 ft). Below the junction of the Trn.lcika the glacier ia quite uniform in gradient t\nd width, which averages 2% km (1% mi}. The upper portion of th" glacier flows in a northeasterly direction for a distan1.-e of 42 km (26 :mi). Hero an abrupt 90° angle occurs and from this point the glacier trends 11::1rthwesterly to the terminus. Tbe gen£>rnl setting bM been described by Griffiths (1952].

Conditions before Advam·e

For ~ pecioa or at }pi!Jlt 50 Yt":l\'0::. tbP lower portinn of the glacier h:w bl't'n wasting awr:.y with littl;:; o: no mo\'t'lnrnt taking place. Photo­gr::q.hs taken in lf!Hi [Griffen] show debrm .. ladi'n 11'!' m tht• t(nnirml an'a. Others taken since 1 fl50 indicate that vt>rtirat wastage of ns much as 200 m (660 ft) bn.s or"'urred during this p<>riod. Aerial views in 1936 (Waahbum] of that portbn of tb(' glarit>r Rbove the bend showed eonditions c~~ntialty ,~;imilnr to th~«:e in 1952. At that time the gladt>r 11hove th<> bl'nd wM rhnractE>rized by Janes of rather mncoth, un~ Neva.ssed ic.e and ltlrge, irr\'gula'f moraine1!1 (Y.g. 1). Phot,graphs taken from McGoMgall Pau m-ar the junet'tre of tht> Tralei!..a and Muldrow in 1916 fOlt,ps1 and 1956 [Mills] show little r.hSJl&e.

3703

..

.:: • - :.... - > .~ •

-"""' . .

.. ..

A l.UITlN S. rotl"'T

(I 5 H) i5 {?;) :25 }-~..L.,l...!rl ,_t,J.-1 I r·-~!,1LII '-l-Lrl.~~ I ,'-l;:-o-1 +-' ........... -"

o 5 SCALE 15

Fil"' 1 'a..f "'tl<l ;.1 r•w1n1 !\!nl.lrhW fih• irr hr!orP nntl •,{h·r ,,h 'l!!l'f· lilm~:l•'\' fpaharr:;: m P:Ulv ,,, , .• ~ •·";\f'ntt'1U•· tlw .qmw Jcl m 1115.! Tlw :uh·:uw<' t. l i l'•·;~d~··•l 1t!'1 maummn h\' Julv \~l'<ll•hn fllKf'U Ul t}J!lt umnth Zd<ti f\'l•t·ah•d 1fl &-!ptembcr W•>W llll tlt~JH•rml·~ ('},ana~.

•

l 1

•

31'0S

r-~---------------------------------""' ""' "":t-' .. -- 1c~ S1.!Rr~a: av, 1952 ~ ICE SJRFA('t sur !957 L - I ~....., O:P M-N

\. ...... , I ,_ ---- 1-..l

~--- \ ~ ..._Cioo. ...... _ ...... _ --

'5 ---...... __

A-8 I

t . ~ I '

-... ... ___ ___ 'l ' i ...... ~' i t fb -I ( f

j j J. I .h

I a ' lh:.u

H<»!IZONTAL SCALE

H<hll'tmtalprufilt·. Muitlrm' ( llmwr 1'he glader uhove WJO n1elcr'i, where nn diB~·ernihlt• change tuok pl!l('i', is not. sho"'n.

Tralt•ika ha1i ""f'mained :thnof:t unchanged. It app£ars that extcnsi'>e u.nwn-vaUey mQYc~

ments were jowering the ice surface o{ the upper Trnleika. l;x>for<' Jul) 6 and thn.t the efie!!ts of such mo,.·em{'nts werE' just heginning to be manift•st on July 16 at the right-angle bend 32 km (2l) mil tlown tlw ~lat·Jl'f.

Early Phase.s of .4dcar~ce

Early in the <~pring of W57, Nntional l':u·k officials first not('(l that the lower gln.ri(•r bad advanced and many n•ports followed describing the glarier as totally changed, mrllllling revt>rnl excited tales of the upper gla<'il•r having 'col­lapst'<i,' or 'fallen in.' This .ut>a was vi..;ited hv st-verol intN('.SH'<i scwnti~t": Nu·~~ { 19571 an~l Millett (unpubh .. hed m:mul'\cript, Pit~)) both re­ti-lrted th('ir ub:ot•rv:ttiun-. 1 n .lilly tht• author made ~<'' Nal ~wrial photn-rH·ommi:-... uw~· ille;ht~ over the are.l. In St•ptemht·r tla<> r. S '!\uvy obtahwd excellent &t'nal 1•hoto~rapbs.

AR ;;N)' litt It> c.-h:mp;(> tnok pl:wt' afh~r dPtt,il('t\

Although no one ac·.u:Ul·· scentS to have ~;('en the k~nning of the J.dy.=~.nce of thr glacier, per­lit>nal obsen·~tions :.1nd photograph2 kindly fur­ni:Ju'11 to the autbnr by vanous peno:ons who bad b?en iu th€' vidnity ill 19~>6 have brought out. rt•rt!tin l*rtmNlt fm•ts. Phutop;raph:'i by Vierrtk taken m:ar th(' right.:mg_le turn in tim lowc•r glact('r on July Hi :-l11•W that lx-low thi:) point the glacit'r was ~most ll.udumged {rom former years. Views up-glscit:r from the same point disclo!".(' notable sh<'anng tn the fonn of ereYaoset.l msd brokE'n ice, particularly along the mnt1wrn m:1r~ins scwral idlNneters farther up t~ valley. and what mny ll(' a. wave of 3.tlvauc­iug tee e:rtenlimg romplf'tt>ly al'ro~ th(' glarit•r at a grca1Pr .•• :mel'. In th<' imm('{bate vtrtmty of tiw n~ht-an~lt• bNld, dw trt•, althnull:h not­::!t'riously di:~turbed, show~ l:!OtnC marginal fr»vas­:;m!l; and n (•lt!Wf.':C: \lrofih•, both of wlueh urf.' intli­t·ti.Uun:- of arit\11). ~hll:- l pH\ :liP ru!'tmunwa­tlof'). h•ml• r nf a mnuntain-rlimbin~; partv un tht' Trtdt·tk;t nt:u·it>r that yMr. dl'fintt~·lv \\it­

fU~""<{'iL r:nl:v pha..;f'!l of tlw adual mnvrnwnt H~· hi!~ dr:'t·ription 1lw Tr:tlt•\l,a. nlai•lt'r w:t>~ htdly «'ff.'V:t.."!'('d w\Jrn t h(> ~roup a.•l t·Hlil'•l tln1 hr:m~'h of tlw ~I11hlrHW m hit' ~[!\' Hl:iti, an•l h;l•l lw­r<Hm• tLlmn .. t l!llp:l!\."ahlt• l1v .hdv ti \h,,ut ,; km (4. mu up tht• Trah•ika. th•· ... nrf.t('(' lt·wl 1Mtl dropp<'(! nn ''"'llmaH"'i tr1 tn I riO ft 1 m thi~ ft. wtwk int1•f\ all>nung thi:J ~<:mw pt•rin•i. tlw ~.{nl· drow nl:u•!l'r a how itfl runtitu•nrt> w1t I, 1hr

uh,.~·nanmH w<·re :)(•IJ:hil m .Tllnl' Iflll7. practi­•":tlly all tlw tnovc>mf'nt ni iN' in tlw $!l:ll'ij•r lJ<'low the !1(1::. lwnd touk j'l;\l'fl ~ll ;t pi'Tlllll nut f Wt"i'<l-

llif.r: tl tnnnth~

S1zturr n.f rr.nn(}f'8 I.nwl'l' 11lar;er Yww~ from thP l)f•n.lli High·

w:w m ! 1t:i7 •li•;r•lo.,.'{i thfl.t tlw hrwvr crlac·i4'r h:ul lwt•n l't•mplt'te·lY tnn~inrm~'<'. "ln<'P ia·4 ob"f'f\P•i m t h{' fall uf Jfil';ii Wh('n' fnrmrrh tl1\' ul:w1•·r h:ttl \lt<t•n a hanUv fi'C'Il!lfl! t1.l1lf' nwr:un.--t•nvt•rt••i ma~'<t a!mn·-t cunt·P.1h·,) ~~·hin•i m31··· tH' b;h·t~ll

..

AUSTIN S POST

METE!!:S

l800

1700

M

6000 FEET

5600

1700!5600

i600. 5200

~r':IO .. ,.~.-~ I J t

470tl 1400

l300 4200

--4400

4000

:noo

120014000

110013500. tOOO

3000

.. "' "".J:'(.'~ 1CE SURFACE 1952

~--------------------·~---,-----------~-.----------------~ Fig. 3. Stx rrosa pwfitea, Muldrow (;.lacier, sbmting chnn.~ in curl,;,;t:':' wvd~ bet~n t~ M.!d lQfi. Positmns of th~e pl'l'lii1es !U'e eho~ ®}'~g. ':.

\1~ tm& am Vall tM pt'Q .. cut tar 1$

•

EXCEPTIONAL ADVAN(;"ES OF Gt..\ClERS overridden anti incnrpgrtlted much of ilK" nearlY stagnant lower portion or the p.cier bUt did ~ completely cover all of an area of telle, ablat.ion­mcreJ~vered i~ d;till! frr-,.m ~ f:l~ ~­v:moo, judged from ve;eWiol.W development tD be n~rly one hundred years ~ or eve11 oldbr (Viereck, private eommunieation). On the esst~ ern side of the advancing glacier this brush· covered ice was compres!e<l and rushed into large ridge-like 'rolls.' Margins of the gta.cia:, formerly concave below the lateral morai.nea, now roae vertically 50 m (160ft) or mo:e above the point of contact with the mo!alne, in most places towering high above its crest. This condi­tion wns prt'S('nt as f&r up--valley as t~ right­angle bentl (see li'ig. 2; also, Fig. 3, Profil!!!t AAl, C-D aml G-Il). Streams from bordering mmmta.Ull! wlurh fonnerly bad dr:Uned through notches in the lateral mcraine were dtu:ntned by t.ho pa.eier and had formed lnkes from which the water now escaped t,h.--ougb old channels be~n the mor&mts and mountain ~opes.

moraines, fantastically broken sera.cs of blu"' i¢e now r(IB('I conspic'lously. Cloo~r examina.tion dis­closed that the ice advancing dovm..p.cicr had

- fl --- ml

5 lO Km lt)l!lll I I 111

4 6 Mi

Middle portitm oi the gll:Jder. Above the right-angle bend the me of the surface of the glacier became progressively less pronounced !Uld was negligible at cross profile 1-J (Fie. 3). For 25 km (16 mi) beyond this point the surface wn.s lower than before (Figs. 2 and 3, Profiles M-N and 0-P). Thlalowerin,g of the ice surfaee was present in all three m.aio~ tributari~ but wu most pronounced in the upper trunk glacier and ~inlly noticeable on the Traleib, which furnish~ the major portion ot the ke invoh_,. in the advance. ~"iovement of this tributary

• Fi,s. 4, Map showlll3 eurf&ec-rooveroent vecton, Muldrow Gla.cier. Dots incicat.e poeitiona of iden .. tifiahle object& ou the glaeicn in 10511 9hotoppha; a~ indicate poaitions o£ same feature& dter a.d· va.nce. The J!()\id line connectins t.ile.ee points ahowt the in!ermi path of movement. Looations of cr011 pro6le* WI shown; fl = firn line; ml = approti­mate iimit& wh;re ehanKe& in muiaee k\vele oc­curred. lloriJontal pT1lfile (Fig. 2) e:ttenW. up C(!%1·

ter o( glacier from broken line below A·B to broken lioo Above 0-P,

amounted til nearly 5.5 km (3.4 mi) agtilils~ 1.8 km (1.1 mi) for the Brooks and 2 km (1.'2 mi) (or the upper Muldrow {F'xg. 4). Most of th~ fiUtUlef, ste<>ply d('~('r,ding tributaries hrul been gr;:ath· altcrt.'<i by this lowering of the m!un gla­cier's surface. The les.st affected were left bang­ing, their point of ron tact with the main glacier being marked by n. sheer ice cliff u much as 61 m (200 ft) high. The majority of these branehela however, bad made large movements !lnd their fonnerly rather smooth surfaces bad become steep cft.S('ades of shattered ice blocks.

Hanging 'stranded! laterll roomines. iee fringt'S, tmd the sheared..aft' lateral tributariEti dea.rly indii!Ale that the ehangee in Ws porl.i<;n af the glacier weta d\1!. tllmost entirdy w a down-valley shift oi the ice a\;OOmpanted by a pronounced 1owerhi! (\{ the glL--ier !lltrf&M oi u

•

. ..

- ·: c ~ ... - ~ - : - c ~~ - ~- • " - - : . . . •.. ,C :

. .• ·.• . - ~ . . . . '<) ' . \ . .. . . f). -~ - •

~ . . . . •' .. · .... • • • 0 ? • •

AU8T!N S. pOST TABLE I (11100 1\) &hove -levol aud ;..,.,...!&~ io bo

------------- aboul the ~um altitude the SDO"''nr. ~ hJI on the ~r. '1.1le areas in different~

above and below the flm limit are g~ven m

3708

-AooumulAtion Aroa

Tn.lelkt. Gl. Btoolu Gl.

93.5 M.6 46.0 1&.0

36.0 21.0 18.0

Table 1. Although t.ba MuldroW Glacier coven appf0%i.

Upper Muldrow 01. All other bra.nebee

6.0 mately 393aq km (152 ~ mi), the portion of the glacier affected by the advanec waa ooly about

81 ·0 167 sq lun (64 sq mi) (Fil· 4). Of this, ffl sq km Total

Abla.tion Are&

Lower Muldrow I.owt'r Tralaka Brooks 01. Up~ Muldrow Relit:, ata.gr.ant. ice,

2{)9.0

104.0 31.0 14.0 12.5

40.0 12.0 5.5 6.0

(26 sq mi) is toeated below croas profi!o I..J in the area into ,rhich ice advanced, and 100 eq km ( 38 sq mi) ia the area in which loss of volmna occurred. The lees of iee from the upper glaciet and ihe gain by the lower glacier appears to be t•quul within the a.ccur&CY of available data. If

9 · 0 an ave~..: surface lowering &hove profile I.J of -15 m ( 150 ft) is assumed, probably a mini-

71 .fi 11111111 fi~Urt•, tltt• net t•Xcllange of it.-e frum the Muldrow Termini

22.5

----------·--- uppt>r to th.- lower glnder is calculated to be about 3.3 kmt (0.8 mi•).

Tuw.l lS4 0

much as 61 m (200 ft), or more (see Fig. 3, c1'"Q58 profile 0-P). Sheared marginal remnant& of ice whieh in pls.ees appeared to have been thrust down-vtilley slightly before being ~ft stri.llded by the lowering of the mAin glacier surface, suggest that the down-vAlley motion may have begun before the lowering.

The movement throughout the rdfeeted por­tion of the gl:l.citr appears to ba.ve taken pl~ in such a way that, although ereva.esed and bro­ken into a fantastic mass of ice pinDAcles, the mAin surface fei~tures consistiug of medial mo­raine! tmd a.vala.nehe debris retntJ.ined clearly ~le (Fig. 1). One feature noted wl'lB

that large areas of heavily debris--encumbered ice frequ~ntly remained a.t a. hl&her level than the adjoinins clean ice. The meditll moro.ine t>~{'nd­ing from the juncture of the Muldrow and Tra.­leika glariers was 1!. notable ~>xample d this, rising above the dean ice on f."ither side almost vertically aproxixnately 30m (100ft), nnd form­ing a wcinUy pinnncled, rontinuou~ wall fur a distance of several kilometers.

Upper glacier. Where the larger tributaries ~coroe narrow and the gradient steepens near the hNl.d of the ma.tn valleys, the- amount of Jowt-ring of the ice 8Urfaoo rapidly dimininhw. Above gueb pointa, including :at leASt threeo­qun.rf.frs or the accumulation area. of the glacier. no d~mible change of surfat>~ levels tonk pls.ee.

Artdll and Volume of Ice, Muldrou.' Advattt.e

The 1957 fim limit oeeuned at 11bout 2100 m

BLACK. R.APlDS GLACIER

In the winter of 1936-1957 the Bbek Rapids Glacier, located 290 km (180 mi) eASt of the Muldrow, advanced approximntelY 4.8 km (3 mi) in 3 months. Eyewit.neae ~tntB of the terminal advance have been pubW!hed [Heme. 1937; Moffit, 1942]. Apparently no extensive studies or e:w:nination of the glacier above the tennin.alnreas were made. Photggrspbs taken in 1942 [Washburn 1 show hanging lateral rem­nants of ice in the upper portion of thls glacier, indicating that this advance was ~prmied by a lowering of the ice surface near the bead of

the glacier.

St1SlTNA. GLAClD

This glacier flows in a. westeilY direction fr(\11\ neves C'Ontignous to the Black Rapids Glacie:r. Wuilbum photographed thia ;lacier in 1942, nnd verticnl photography [USGS) taken in 19..~ shows that the glACit>r bad advtmoed, p~Y in 1952 or 1953, with ice movements of 4 km {2.5 mi) or rnow, ~with a pNnouneed low- ... t>ring of the surface of the upper ct!\Ckr.

YAli iRT GLAClllA

Aerial pbot~phs take:u blr Wuhrn\11\ m 1942 ahowtid that this ~. 9§. km (00 mi) wtst. of 'ite p,Jatk R&pids ataei!f. wu ~ callY crcv~, appUtUtly ~ to • rapid ad-

•

.. .

approxi­)D of the ty about 37 Stl km le I..J in :>0 sq km i Yolume ~r glad.er ars to be • dab.. If rofile/..J v s. mini­from tlw

t("d to lX"

ek Rapids sst; of the 1.8 km (3 nts of the :d [Ham.t, ) mensive above the

bs tikcn in bteral rem­this pacier .. eoompanied the OOt.d. or

reetio~from lids Gl~r. ~r in 19-12, .ll.b.--n in. 1254. ed, probablY nt. of 4 km 110Uneed 10"6l­~dn.

EXCEPTIONAL ADVA~~CES OF OLACIEM

20 .... TEMPERATURES -A-·lZO

II o•l...~r :s-c•

t.. 1 .... ' z ~

4 Cm.

..... 3 1· , ln.

em. s z

PRECIPITATION

4 3 2 I 0 0

L I J

Fio. S. M- monthly tempetatureB and precipitation at McKinley Park B'Ation (elevat'on 100 meteno). l I

Significant A~tctl va.,}OO then t.aking plact'. The U. S. Gt:illogical Sm,vey photogr&pb.s taken in 1952 sbuw this gbt.eier to have been almost free of crevasse!J.

The glaciers covered in this report h~ve 1t.

number or features in common:

CoNCLUSIONS

It bas ddinitely been determined by examinl!.­tion or aerial photographs and by personal ob­servation thAt ell the above advances took place without contemporary movement of any other glacier in the immediate vicinity.

1. All ht.ve a fairly long, narrow main stem of relP..tively low gradient {slope in the middle reach avenging about 30 mjkm (120 ft/mi). AU but the Yanert, which has one, b.&ve three or more major tributary valley glo.ciers. NomuillY, a reach 8 km ( 5 mi) or more in length at the terminU! is virtually stagnant and covered mth

UntUWll Surfar~ Fe.:.tures The glaciers discuESCd above have simi1a.r1 al­

though unusual, medial moraine patterns. These consi:'!t of la.rge bulb-hke loops in the moraines which frequently extend a.I.most from one side of the glacier to the other. Nearly identical loops may be seen to repeat at interv&1s. Some­what similar moraine patterns are found on a very few other v::Uley glaciers in Alaska, one being the West Fork Chulitn&, Tbase moraine loops are prouably c:aused by intrusion of fa.st.­mn-..ing tributarit.s into the sl:>wer main stream. The moraine loops are displaced down the vallf:Y by &dvan~es of the trunk glacier. When the movement of the trunk glo.cier ceases, new ice bulbs are formed by the tributariea. Aerial pho-­tographs (USAF and USGS) or the Bllck Rap~ ids Glacit'r in different yeArs show defortnAtion of this nature taking place.

debris. 2. Each advance, with the possible exception

of that of the Yanert, of which little is kn<>wn. was pn•t>Nl••d by a long period (at lNl.st sev€'r31 decades) of inactivity in which tbr glQfier ~wss very innrtive and thinning in its ter:ninal

regions. 3. As a ~ult of tbe ad,·anee, the suda.ce

levd in tho middle re.ache! of the trunk: a.nd trib­utaries is lowered. The ~rfa.ce in the terminal atNl rises, n.nd active i~ overrides stagnant, debris-covered ice, but no net change in mass OC<lUTS. The $Urface changes in elevation m&Y amount to 60 m (200 ft) or mote.

4. Sudaet'l f(',atum are rusplacro down-clader by several kilometers but otberwil:IO are little distorted by thfl advance.

5. Similar advanet.>s app::uently h:w~ oeeun:ed in the past, and, in oome ~ &t least, this may be a periodiellly reeurrinc ~·

• •

"

..

·. • . I . ' • . . ••• - •• ••• ~ • J '\' • • • -

. . . . . . . . ~

S2

13 hl.

tg 21 em. ANNUAL

2& PRECIPITATION II

TEMPERATURES Yay t st. ~o Ott. 31 st.

l I I l I l .J : I I 1 ! l I l ! l ~...J

p~C<*IU

~ are bmm to be wry teniitive to clirnatic variation, ao it is only natural t.o look first to this~ the direct. eaure of thete ~. Attempts to correlate the ~nt. c!a.cial bbtory at tOC lhck Rapids Glacier with ot~ glaci~s [Pm, 1953] imply ~ptanci! of e:limatie v:ui­ationl as the cli.Nict eauae of the sdvance of tbi! pcier. However, the ad"\-*1\.Ur:e of gll.cien in. t.he Ya!Luu.t Bay &%t'& in the •-err early I!nr• 'fi'&S ~ to Q....~nna.! avslsnehinc of IMW du~ to earthquske [Tarr atsd U~ 1914). tm id~ wh\ch bas pined widespread aeeeptunoe. The ~bility that a eycle of advAnw -may be caused directly by wastage of a glaeim· wu menttom:d bv Forcl and IDcbt~r in the 191h ("~ntury rR~ stll, 1899] and bas been reported f!.!(;ently [Stmf]-Ded:$r. 1957; Dew, 1954], hut nppM• entb' it has not been sttt.>pted geneOOly by ..rorke11'8 in the fie!d of pacie:- dynami~. C~ 11ariatian. No record! lave ~

kep~ which din;etly indtcnte we.(lther ('A:nd!Hons on the Muldrow or ot.Mr gl-.oi0rs d~ribed in this repurt. The general elims.tie patt~mt b@W•

ever, iJ indieAtM from NOOI'd! kept aEOO 1900 at McKinley Plftrk Station, located approxi-1?-!ltcly midwn.y lretween the Muldrow and Black Rri~ds ~~ieas.

Figure & ;ebc»wa the m~'!m n:u.mthly ternpt>'fa-

tute!l and precipitAtion at McKinley Park ~ tion for the 27~yeu period of rooord prniou3 to th6 Mcldrcnr &d.van~. It ri1 be no~ that the bulk of the ~:-ecipitation ~eurs durinc tM rummer mcntbB. Cool3Ummer ~peratnres t.nd a rtSUltant loll-ering of the fim line would result in a.l.&~ inere.uc m the tu·~. or mow accumula­tion in th~ ~r ha:ml. FigUre 6 sholfS the run­ning 10-:V"eal' mt>an for ~by 1 through Oetobet 31 t£Wpernturcs at McKinley• Park St11tion a:ud the M,nu:U prc~tpitation owr the 27-ytar ~riod of t>teord. l<n1nl this1 no de-ar inmCllltion of &ny general climatic eban~ ftworinr glacier growth is ap~t.

l)(t:;;pitt! tbi9, the p~blmy or wr~t local in-erea.&'S in snow a«mnuhltt~n musi oo en!llid· {'rt-U. It will b;;.> Mt~~ that:

1. c~ntiguous r;tad~ra (Susitna an'!i Bhck RApids lim) diti not ~"'a simil&rly at the trun'<." time. ln fact. the ebanp "teve&!C1i l'1y tt.l· tcnsive (l'(!Vslrtl at tht~ heM of thtl &:!itna Glc.{•ier in 19M wl.'ls :O<!!UWk~h. Tr~ cttin.Rn;:; ~n only a. few hundred mt'!t~m from & pomt in e. ('iJID..'llOu firn frotil \'rllj\:!1 tim.Urtr e~~DI

• due to ioo moving in the opp.o:rlre direetlol\ t»o eurred durlni the B!aek Rapids 1\dv&ne?\l in lfl37. Dunnz thi'l intf'rv"M ll comp!e'OO rove~ d the dywmie ~:vnditio.n of tho two ~ctk!'o t'tt!Zk Ii'ite.

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Fill- 7. M•P ~ -- o{ ....,dod eulhqWike epi,..,.,. in ""'""' A!Mb, ....! !heir rda>iu> ' \n the Muldrow • Susit.na. and Black Rapida gladet'll

The advance oi the MuldrolV was not the result. of ice being dislodged from surrounding mountains, because the ateeper. Ul'Jler po:.tions

widely dlffere:nt inte~·als in time. Adva.n~ eyekd cmnpletely in & matter of months; thoro­fOM t.bree would not seem to be deb.yed re­spomes to a suitable general climJ,tic variation.

3. In at least one known ease (?nuldrolf'), the amount of ke in the ternUnal advance equaled the amQUnt of ice depleted in upper reaches without any co1't'CfJPOnd.inl'refilling' of the ae~ cumulation ba..r.in. There was no di!eemible net addition of roMS to tbf.' glacier. Indic~tions are that the Black Rapids and Susitnll. advances were ees.w:ntially the !!AIDe u that of the Mul­drow. Th~refore, even if a localised, ~radio dilrtribution of ditnatie changes bad Ot'eumd, it oould not have done more than act as a triggN'.

BortnQ1!0ku. ;~ ll these glaciem oet:UPY val· k:ili which are believed to follow !\ major fault Jme. With but few exceptions, other glaciem situ­-~ f&rther east IUld farther west and meupy­inl portio!UI or thi! same fault ~em show at leMt .110me erratic surface features. while on nearby glatier! in valleys not JI.!SOCi&ted with the (a.uit IUch feature« cenerally Ate absent.

o£ the glacier were unaffected and no extensive reeent :wa.bnehing was obeerved anywl'.were in

the b&sin. Figure 1 shows the plotted position~ of tpi-

eentt'rs s.nd the int~ll!!ity And d"t~ of llll re­rordttl Nt.rthquakes in this 1'-"rt of th~ AlaskA Rungr. No 1hn.'t"t relat1onsiup b<>twf'\'U there shocks and the v:trious ghl.cier adva.nm is evi­dent, although the earthquake of March 2, 1956t ct.'ntering 50 km (30 mi) nortb~~st o( the Mul­drow, or the March 30 shock for wbieh no epi· eentN' ws.s plotted; should be "onsidered as 11~ible triggering mechs.nistns·

The possibility that e~Lrthquakes iormin, a. shock ws.ve within .. gla.der would result m .. eawtrophie D.dYanee bM \)(ten proposed by A. E. Harrison (private communicstion}.

No earthqua.k('.l!l hl've been !'e'Cotded whieh show any relAtionship to the Black Rapids. Su.· sitna, a.nd Yf.\Dert advance~. MoiU [190)

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3712 AUSTIN 8 •. POST

stAted withouL elaboration that c~r.rthquakes did York. Tba U. 8. Na.,y, U. S. ~__.;~~ ooour in the vicinity t>f the Black B,apids in 1936 Bottotl MU1111um ol ~~ Uu.iverlit>" ua _. ltlld 1937. The fact t'-~t nearly -", tlle ... t .. -t ...... in iqt.on, Ohio State UmVCilllitr, and tho Nat.Wui u.u. a~-~ P'Ch••" Park Si!lf'IWe are t.baDked for their c.ooparation· the Alub RAnge which diarJay errD.tiG flow Dr. Mark F. Maier and Mr. Edwud R. ~ charactemtica are located aloog the same fe.ult rendered valuable aaoi-ta.Tlee· systm1 does wggest. a po'JSible eonnootion in trlgserin' wcll advan~, a connection which would bear more detailw investiJation.

Dynamic conditio111.1. Most evidence, inelud· ing published earthquake reeordst suggest~ that. the advlllces were not due to any pervasive ex· ternal cause bt~t wert' thfl t'r!tltJt of unmble dyn&mie c:ondnions in the particular glacier sy~­t.ems. The rr...echanism indicated is that of an ice 're;ervoir' ! >rming m the middle portion of each 1laeier Md beinl filled over a period of yean with ke ...-hieh ftow:s in from tributaries while the stagnant lower terminal portion of the r;ta­ci:tr i!· bein1 rtduced by abl&tion. When certain entic!l condition! are reached the glacier be­('O!DE"$ unstable and a eudden brief movW~~nt or the ice takes plaee. This mm:cment so depletes the reservoir area that whf'n thtt ice oomt"s to rest. '\irtual sblgnation OCCUr!! in the lower gbeier and the pro<'CSS is rtprattd.

• .trhou:k~""""· This study w:ut undertaken as tt. pllrt of lOY Project Ul under the spon!Of­!lbip of t.he Americ&n Geographical So..'iety of NeW'

06i~ Ardito, An exet'Ption:U ~ advance in. the l{arakoram-Ladakh regioo, J. Geol., I, 383-

385, 1954. Oriftit.h.IJ, T. M., Glacial geomorpholoiY on the ).ft.

McKinleY tr\Ji.1l8if, Al.Mka, Proc. 8th GenMfd A,_ .emblt~, 11th. Congr., Inurn. Geograph.. Uaitm, Waahington. D. C., 331-336, 1952.

Haneer J.ll .. The rerent advanoo of B..luk RapiM Glacier, J. Geol., .:6: 77~'183. um.

M.oftit, F. H., O..olOCY o{ the Gentle River Dis­trict, Aluka, U. 8. Geol. Survey Bult H$-B, 14&--157, 1942.

Peri, T. L., Multipi:o ~ia.tion in Ala.llb, ('. S. Gem. Burv«ll. Ci:rc.189, 13 pp., 105'3. (A~), Bull. Geol. Soc. Am., 1008. 195'1.

'Rll!Bell. 1. C., G!Atiere of North AmeTiea. Ginn & Company, Boston, 151, (210 pp.}, 1899.

~treiff-Becker, R., Glacier t&dnnreJJ apparent. and real, J. G~l-, S, 151, 1~7.

Ta.rr, R. ::;1. • an~ I •• M.rtin, Allu!b G~ Studiea. Nl!.tion''. Geot,'nlphic Society, Wubincf.on, D. c .. 180-197. (496 pp.), 19!-4.

(Mn.nueeript. nee~ Ma:v 23, 1950; re..utd Augttrt!. 121 1960.)

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