Bu11etinofGlaciologicalResearch22（2005）99−107

9タ◎JapaneseSocietyofSnowandIce

Debris−mantleformationofWrputuGlacier，theTianshan Mountain＄．China
ShujilWATAl，ShinjiroKURODAl．andKADERKezer2

1DepartmentofGeography，TokyoMetropolitanUniversity，Tokyo1920397Japan
2XingchangInstituteofEcologyandGeography，ChineseAcademyofScience，Urumqi，China（Received October6，2004；Revised manuscriptreceived NovemberlO，2004）

Abstract
Asmallvalleyglacier，WrputuGlacier，intheUrumqiRiverbasin，theTianshanMountains，has
atongue−Shapeddebrishi11infrontofadebris−freeglaciersnout．Twotopographicalmaps，SurVeyed
in1983and2003，indicate that the debris hillsurfacelowered5−10min elevation for the20−yearinterval，andthissubsidenceoccurredontheentiredebrishill．Thecauseofthesubsidenceisablation

Oftheunderneathglaciericesothattheentiredebrishillcontainsice．Thismeansthatthedebrishill

isadebris−mantledglacier−SnOutratherthananice−COredmoraine．Thedebrismantlehasoriginatedfrom the debris−rich basaトicelayer of the formerly advanced and overrode preexistent glacier．Its

SCenariois as follows：The preexistent advanced glacierTSnOut turned to a stagnant snout by thenegativemassTbalanceoftheglacier．Inthefollowingpositivestate，glacierthickenedandincreased
its movement rates．The active snout with debris−rich basalTicelayer overrode on the debris−freeStagnant−SnOut and continued to advance．The preexistent debris−free glacialsnout turned to thedebris−mantledglacieraftertheoverriddenglacierstoppeditsadvanceand retreatedasleavingthe
residualdebrisTmantleon the underneathstagnantglacialsnout．

1．lntroduction
Debris−mantled glaciers with continuous suprag−
1acialdebris−and till・mantles are commonin high−reliefmountainenvironments，SuChastheHimalayas

and the CentralAndes．Many rock glaciers are tho−ught to be deformed from debris−mantled glaciers．
Debris−mantled glaciers and／or rock glaciers were
found even on Mars recently（Head and Marchant，
2003）．More understanding of the debris−mantled gla−

Cierisnecessary todiscusscoldenvironmentsinand
OutSide of the earth．Thusimportance ofintensive
discussion on the debris−mantled glacierincreasesin
glaciologyandglacialgeomorphology．

freeoneduringthesuccessiveadvances．Notracesof
large geomorphologlCalchanges such aslandslides
and rock avalanches were foundin the upperglacial
basinsurroundingtheaccumulationarea．
The present study describes the morphologlCal
ChangeofWrputuGlacierbetween1983and2003，anddiscusses the processes for the buildup of the supra−
glacialdebrismantleofthedebrishill．
2．Research area and research method
ヱノ． 斤l−∫lⅥJ・（、／J（〃で（7The upper reach of the UrumqiRiver，the Tian−

Shan Mountainsin western China，is situatedin an

alplne ZOnelocated above forestlines．Many rock−A smallglacier，Called Wrputu Glacier，in the peaks over4000m a．s．1．constitute the basin divides

Tianshan Mountains was re−SurVeyedin2003by theand many smallcirquesand valleyglaciersoccuron
thesemountainflanks．Accordingto themeteorologip
The resultsindicate that a tongue−Shaped debris hil1
Caldatameasured by theTianshanGlaciologicalRe−
locatedinfrontofthepresentglaciersnoutisadebris−
SearChStationoftheColdand AridRegionsEnviron−mantled glacialsnoutconstructed recently．Thiston−mentaland Engineering ResearchInstitute，Chinese
gue−Shapeddebris hillwasthoughttobeanice−COred Science Academy，locatedin the main valley bottorn
presentauthorsaftera20yearsinterval（Iwata，2004）．

frontalmoraine．Themainpa二rtofthepresentglacier at3546ma．s．l．，meanannualairtemperatureis−4．5℃，
and annualpreclpitation，the70％of totaloccursin
summer，is468．6mm（Ji，1980）．Thelowerlimitofthe
permafrostis3100m a．s．1．（Ji，1980）．
a completely debris−mantled one to a typicaldebris−
WrputuGlacierisoneofmanyglacierslocatedat

SnOutisatypicaldebris−freesnoutonwhichonlyfew
bouldershaveemergedfor20yearsbetween1983and2003．Itisquitepeculiarthatoneglacierchangedfrom〃椚Bulletin ofGJaciologlCalResearch

Fig．1．Study area and Wrputu Glacier（No．6Glacier）in the upper basin of the Urumqi
River，WeStem China．A二glacier，B：Litt】eIce Age moraine，C：Holocene moraine，D；Last
Glacialmoraine，E：Rockglacier．

Fig．2．Wrputu Glacier constitutes a debris−free main valley glacier（l），a Smallcone−typeglacier（ice talus）（2）withadebris−mantlein thelowerpart，and debris hill（3）infrontof
debris−freemainglaciersnout，TakeninJuly2003from thenorth．

around the Tianshan GlaciologicalResearch Station，

SteepSlopeandturnstotheeastinthevalley，andthe

inlength，With4300mofthehighestendand3750mof
the present front．Glaciersin the area are classified
intocold−typeglaciersbutpartsoftheglacierbottom

locatedinfrontofthepresentglacierfront．A central
lower partis bounded by horseshoe−Shaped higher
marginalpart．Thehighermarginalpartwasthought

andisnamedNo．6GlacierbyChinesescientists（Fig． tributary oneis a smallcone−type glacier（ice talus）
Withadebris−mantleinthelowerpart（Fig．2）．Aton−
1）． Wrputu or Wulupte is the name used bylocal
Kazakhpeople．Thisisasmallvalleyglacierofl．5km gue−Shaped debris hillwith steep frontalslopesis

ofNo．1Glacierattain atthemeltingpoint（Shi，2000：
60−61）．The glacieriscomposed ofa main valley gla−cier（the north snout）and a tributary cone−typegla−Cier（the south snout）．The main oneis a debris−freeglacier whichflows to the north on the north−facing

to be anice−COred moraine（Cui，1981），and oneofthe

authors，Iwataobserved thatalargecleariceexisted
under glacialiceinside the higher marglnalpartin

1983（Iwata，2000）．Thetongueshapedhi11seemstobe

asimilarformofaterminalmoraineorarockglacier．

Iwata etal．

／（リ

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Fig・3，TopographicmapsoftheWrputuGlaciersnoutandthetongue−Shapeddebrishill．Fig．3L
IwassurveyedinJuly1983byIwataand Chen，and Fig．3−2inJuly−August2003byIwata
and Kuroda，Contourintervalis5m．Dottedlinesin Fig．3−1are boundary of the following
division A−D．A：main valleyglaciersnout，B：COne−tyPeglaciersnout，C：highermarglnalpart
Oftongue−Shapeddebris hillwithsteepfrontalslopes，D：Centrallowerpartoftongue−Shaped
debris hill．Solid squares withnumbersarelocationsin the text．

ヱヱ一札ハ（−（川ソJ椚（リ／川（′InJuly1983，IwatasurveyedWrputuGlacierandcompleted a geomorphological map by plane table

SurVeying with an electron distance−meter（Fig．3−1）（Iwata and Chen，1987），When theJapan−China coop−erativeresearchwasconductedintheareaaroundthe
Tianshan GlaciologicalResearch Station．After 20

years，inJuly−August2003，thepresentauthorscarried

Outtheresurvey by thesamemannerasthatin1983

COntrOlpoint．The authors carried outfield observaNtions on debris production from the present glacierandonsedimentaryfeaturesofdebrisonthetongueN
Shaped debris hill．
3．Results
3．ノ．肋ゆわoJogわαJcゐα乃ge5わeわ〃eeれノタ＆ヲα乃d2ββ3

Two topographicalmaps，SurVeyedin1983and（Fig．3−2；Iwata，2004）．PointYin Fig．3wassetupon 2003，indicate the morphologicalchanges of the pre−the bedrock in front of the debris hill as a common

Sentglacialsnoutandthetongue−Shapeddebrishillof

BulletinofGlaciologicalResearch

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Fig・4・Verticalchanges of the glacier and debris−hillsurfaces 7were 0 computed from the1
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Wrputu Glacier for recent20years（Fig．3）．Vertical

VanCingorrisingitssurface．

indicated bydifferencebetweenthecontour−1ine val−uesonthetwomaps（Fig．4）．

ヱノ．2．肋ゆゐ0わgわαJc／‡α乃geSα乃d s〟りわceJo仙eγ〜れgO／

Changes of the glacier and debris−hillsurfaces are

ユJ・ノ．針什川J（川（ブⅢ亘汀l、／（り（けf噸■（イ仙▲君・／（J（、／〝The front of the main va11ey glacier（the north

SnOut）retreated more thanlOOmindistance，and theglaciersurfacelowered30−40minelevation，themaxi−

mumvalue，Obtainedatthe2003frontalpositionofthe

glacier，is53m．

The frontalpositions of the tributary cone−typeglacier（the south snout）are not clear because the

SnOutis covered by supraglacialdebris−mantle．The

lowerendofthiscone−typeglacierseemstocoincide
Withthebreakofslopewhichislocatedroughlyatthe

35m contourline bothin1983and2003．If thislower

boundaryis accepted，the frontalposition has not

Changelargely．The supraglacialdebris−mantleis

COmpOSed ofrelativelylarge and angular blocksand

apparentlyincreasesitsareafor20years（Fig．3）．The

steep back slopes of the glacier indicate that debris
WaSSuppliedontheiceconebyavalanchesandrock

抽（・（Jp／〃イ∫／J／／／

The outline of the tongue−Shaped debris hill
Shows the almostsame formin these20years．This
debrishillistopographicallydividedintothreeparts：

the steep frontalslopes，the horseshoe−Shaped mar−glnalhigherpart，and thecentralbasin bottoms．The

position ofthelowerfringe offrontalslopes has not
Changedfrom1983，andnosurfaceloweringoccurred
Onthefrontalslopes．Figure4showsthatmostofthe
top surface of the marginal higher part keeps theSame elevation，eXCept the northwestern end（low−ered）andsoutheasterncorner（lowered androse）．In−

nerslopesofthemarglnalhigherpartpartlydecrease
3−7minelevationandthecentrallowerpartlowered

5−10m．Verticaldisplacements of glacialand debris
hillsurfaces are shownin sectionsin Fig．5．In a−b
SeCtion（of the main valley glacier；the north snout），

thesurfaceloweringoccurredinthepartnearglacial
frontandcentralpartofthedebrishill．

falls．Thisindicatesthatthedebris hasbeenaccumu− ユヱ」R−（JJ〃作∫（）．／、∫JJJ二Jt汀＝左−か由りJ＝九−（／（・加点／J／JJ
lated by meltTOutOftheglacier．

Surfacelowering of1520mis observedin thefrontalpart of the debris−mantled cone−type glacial
SnOut（Fig．4）・Fourcellswith2r4msurfacerisingare
indicatedin Fig．4（vertical16−17，horizontal13150f
Cellnumbersin coordinates）．They coincide with awideridgebetween40mand55mcontoursinFig．3−2．
Apparently，a part Of the cone−type glacieris ad，Based on features ofdebris，thedebris hi11is cle−arly separatedinto two parts：the north and southparts．lnthenorthpart，thesurfacereliefisgentle（Fig．
6）and most clastsin the well−SOrted debrislayerare
CObblein size．The surface clasts form a stable andCOmpaCtgrOund−Surfacelikeastonepavement．Many
microformsindicating subsidence，SuCh as step−1ikehummocky−forms on slopes andlinear depressions

1wata（Z亡α〜．

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distance（m）

500

Fig．5，Verticaldisplacementsoftheglacialanddebris−hillsurfacesin thesectionina−binFig．3．

Fig．6．Surface features of the debris hill，1：The north part of the debris hi11．The surface
reliefis gentle and the debrisis wellsorted and most clasts are cobblein size．2：Large
Clastsarecoverthesouthpart．

Withcracksatthebottoms，WereObservedinthispart． theeasterncornerofthecentralbasin（Seelocations3
They occur evenin the marglnalhigher part whereand4in Fig．3u2）．The thicknessof thesedebrisman−the surveyed results show no apparent subsidence．
tlesis even，One SeCtionisl．5m and the otheris2m．
The centralbasin−bottoms are mainly covered with
Thelattercase，amatrix−SuppOrteddiamictonlayeris
Pebblesandfinermaterialstransportedanddeposited
COVered with a thinfluvialgravellayer（Fig．7）．The
bymelt−Waterfromtheglacier．
diamictoncontainsafewlargeclasts，butiscomposed

The south part of the debris hill shows rugged

Of relatively we11sorted sma11clasts with abundant

topographylike glacierkarst with hollows，icecliffs， fine matrix．As faras the observed sections of surface
andlineardepressions．Thesurfacedebrisisillsorted
debrisindicated，the debris−mantleis thin and uni−
andincludesmanyhugeblocksofdifferentlithology．
formin thickness，and the underneath glacier−iceis

Thesefeaturesaresimilartothoseofthemanydebris−
mantledglaciersinruggedmountains．
Three exposures of supraglacialdebris−mantles
Were Observed atice cliffs during thefield observa−

thick with over a few tenth meters．

ユユ（抽∫（リ■…／J＝川／肋lリノ＝／JJ…〃tI．l・−g／（汀／〔リ▲∫仙〃J／

Frontalpart of the main valley−glacier shows ation．In1983，alm−thickdebrislayerappeared atthe COnVeX bareTice snout．Measurement of glacial−flow

topoficecliffinthesoutheasterncornerofthehigher

marginalpart（seelocation2inFig．3Ll）．In2003，tWO

exposures were observed on theice cliffslocated at

ratesat5pointsonthesurfacearoundlOOm farfrom

the frontalmargin recorded average values of O．32−
0．93cm perday fromJulylO to27in1983（IwataandBulletin ofGlaciologlCalResearch〃りChen，1987），aCCOrdingly the snoutis an active one．
Frontalpartofthe main valley−glacier，however，has

being retreated aboutlOOrnin these20years．The
authorsobservedthatglacierreleaseasmallquantity
Of debris from the steep glacier front as the glacierfront has retreated．Debrisincluding clasts appearedalongnearlyhorizontalshear−plainsonthefrontalice

byshear−uPandmelt−Out，andfelldownontothefootin frontoftheglacier．Althoughmorethan30msur−

facelowering hasoccurred atthesnout，nOaPparent
supraglacialdebrishasappearedonthesnoutforthis

20years．Thisdebris−free featuresdistinctly contrast
With thefront of the tributarycone−tyPeglacier（theSOuth snout）of which surface has beenlargely cov−
eredwithsupraglacialdebris（Fig．3）．
Basaldebris−richice with2−2．5m thickness was

Observed at the bottom of the glacier snout near thefront（Fig．8）．Clastsandfinematerialsoccupy40％involume within clearice which has attached by re−freezing，andtheclastsarecobbleandpebbleinaver−age size，butlarge clasts with O．2−0．3min size areincluded．The clastsin the basal−debris richice−1ayer

showaplannerstructureparalleltotheglacierbed．A
numberoftheseclastshavefacetswithstriation．This
SuggeStS that basalsliding occurs at theinterfaceof
theglaciericeandtheglacierbed．Aslitbetweenthe

basaldebris−richiceandtheglacierbedwasobserved．

Theglacierbediscomposedofclastsfelldown from
Fig，7．Section ofdebris−mantleon theiceclifflocatedat the eastern part of the centralbasin（location4
in Fig．32）．2：Debris mantlewith2min thickness．
The matrix−SuppOrted diamictonlayeris covered
Withathinfluvialgravellayer（1）．3：Glacierice．

debrisTrichice and sediments moved by melt−Water．

Onthegroundinfrontoftheglaciermargln，Clodsof

fine debris（Silty clay with clasts）settled from thebasaldebris−richlayer were observed．MeltTWater
COmingoutfromtheglaciertransportsgraveland貝ne

Fig．8．BasaldebrisLrichice at the bottom of the glaciernear the front（locationlin Fig．3rl），1：Glacierice，2and3：Basaldebris−richicelayers composed of clearice and debris，4：GlacierbedIwataetal．

PreSentdebris−freemaingJacjersnout

ノ♂5

debris hillFig．9．Schematic section of the present debrisrfree snout and the debris hi11（preexistentdebris−mantled glacier）．

materialsanddepositeddownstreamtheglacierfront．
4．Discussion
4．ノ．』れgCe−COγe∽0γ℃g乃β0γαdeわγZ5−∽α花王JedgJαCfeγア
The results show that distinct subsidence oc−

Curred on the debris hillin the upper（western）part
near the glacialfront（Figs．4and5）．Cause of thislarge subsidence is nothing except ablation of theunderneathice．Asmentionedabove，theexistenceof

areas by any geomorphic processes such as ava−

1anches，1andslides and debrisflows．The thirdis de−brissedimentationonglaciersbywastageofsurglng
glacier snouts during repeated cycles of glacier sur−ges．Thefirstprocessesareordinaryonesoccurringin

mostdebris−mantledglaciers，andthesecondoccursin

some accidental occasion such as the rock avalanche

OCCurredin Mount Cookin1991（Chinn etal．，1992）．

The supraglacial debris mantle produced by surges

icebeneaththedebrisinthemarginalhigherparthas

WaSObservedinmanyglaciers（BennandEvans，1998：547）andglaciersin Kamchatka（personalcommunica−
tionfrom Dr．T．Sawagaki）．

entire debris hill，eVenJuSt OutSide of the present

brisin the past as wellas at present，becauseits

debris−richbasalicemeansthattheiceofthepresent
glacialsnout separates from theice−maSS under thedebris mantlein front of the snout．This means thatthe present glacier snoutisindependent from theunderneath glacier bed that contains glacierice．
Thesefeaturesstronglysuggestthatthedebrishillin

landformssuchaslandslidesandslopefailurescould
notbefoundonbackslopesoftheglacialbasinsothat
the direct debris−Supply onto glacier surfacesis not
the cause ofsupraglacialdebris−mantle of thedebris
hi11．No surge has been recorded on Wrputu Glacierand featuresofglaciersandlandformsshow nosign

PreSentdebris−freesnoutoverridesonthepreexistingtion．

already been known，and themarginalpartwastho−ughttobeanice−COredmoraine（Cui，1981）．Thissubsi−
On the main valley glacier snout the melt−Out
dence，however，SuggeStSthatinsideiceexistsin the processes enable to have formed thesupraglacialdeT

debris−freeglacierfront，andtheicemayextendunder englacialdebrisisscarceasnodebris−mantle hasap−
the glaciersnout．AlthoughtheexistenceofcontinuT
peared due to the30−40m surface−lowering for these
OuSice beneath the glacialsnout，eXistence of the
20years．In addition，any traCeS Of mass−mOVement

frontoftheglacialsnoutisadebris−mantledglacier−SnOut rather than anice−COred moraine（Fig．9）．The
debris−mantledglacier．

Ofsurging．Besidestheseprocessessomeotherproce−
SSeSarerequiredtoexplainthedebris・mantleproduc−

4．3．fわ5ざよわJec（Z〟Seq／Jゐedeわγ才5−∽αれf′β4．2．ProcessesノもγmfれgS視♪γαggαCiαgdeわγfs−∽α乃fge

Thedebris−mantledglaciersnout（thedebris hill）

gives a curious fact that the glacier shifted from adebris−mantledone（thedebrishill）toadebris−freeone（the present snout）at the next advance．Itis quite

peculiar that glacier−Surface features changein a

Shortinterval．A reasonable cause of debris produc−tion should be discussed．GlacialgeomorphologlCal
Studiesin presentstate recognizethreeprocessesfor

SuPraglacial−debrisproduction（forexampleBennand
Evans，1998）：Thefirstissupraglacialmelt−Out prOCe−

sses which include emerging and accumulating of
englacialdebrisonglaciersurfaces，andthesecondis
directdebris−Supply ontoglaciersurfacesin ablation

In discussing a possible cause of the debris−
mantle，SeVeralfacts andinferences areitemized asfollows：

1）Themainglaciersnouthasretreatedforthese
20years and more years，and this means thatit had
advancedandoccupiedthelargeareaofthedebrishiu
in thepast．Thestableandcompactsurfaceofdebris
hi11seemstobetheresultofthepastglacieroverrid−
ing．

2）The main glacier snout has a debris−rich ba−
Sal−icelayer with atleast a few metersin thickness．

The features of debris−mantle such that arefine andrelatively we11−SOrtedinsize，andthinand uniforminthickness are very similar to those of the debris−richBulletinofGlaciologlCalResearch／り†J

1．Themaximumadvance．FrontaImorainewasbuiJtbymeJt−OUt4．TheactivepartofthegLacierthrusteduponthestagnant

PrOCeSSeSduringtherelativelysteadyperiod．

2．Surface10WenngOCCurredonthestagnantsnoutbynegative

5・Readvancedglacierreachednearthemaximumfront

3・lncreaslngOfflowvelocityintheaccumulationarea bypositive

6．Shrinkageofthenewsnoutbynegativemass−balance・
Debrisinthebasaトicelayerwasle代ontheoldsnoutL

mass−balance．

mass−ba［ance，

Fig．10．Scenarioofsupraglacialdebris−mantleformation by advancingand overridingglacier・Theoverrodeglacierleft
debrisinthedebris−richbasal−icelayeraftertheglacierretreats．

basalicelayerunderneaththepresentice−freeglacier
SnOut．

3）Abovel）and2）1ead to a deduction that thedebrisin the debrisTrich basallayer of the advanced
glaciermightbeenremainedasadebris−mantleonthe
preexistentglacier−Surfaceaftertheadvancedglacierretreated（disappeared）．

4）The2．5−2．Omthickdebris−richbasal−icelayer，Whichis the observed value by authors，COrreSpOnds

ingglaciers，nOeVidenceofpastglaciersurgehasbeen
recognized on WrputuGlacier．
As mentioned already，the glacier advance andretreatin this scenario were not due to surge cycles．
The features of glacier variation might have beenreflected from the climatic change during the Late

Holocene．The climatic change，however，have notbeen understoodin this area．

to al．0−0．8m thick debris−mantle due to decreasein

5．Conclusions

the debris−mantle on the debris hi11．
Basedonabovel）−4），theauthorsdeduce thatthe

WrputuGlacier，aSmallvalleyglacier，intheup−
per reach of the UrumqiRiver，the Tianshan Moun−tainswassurveyedin1983and2003．Atongue−Shaped

VOlumeofthebasal−icelayerbymeltingofinterstitial
ice．The decreased valueis not far from the values ofdebris‑mantle on the debris hill was derived from thedebris−rich basal−icelayer of the advanced glacierdebrishillwithsteepfrontalslopesislocatedinfront
Ofthedebris−freeglaciersnout．

Two topographicalmaps，SurVeyedin1983and2003，indicatethemorphologicalchangeofthepresent
Fig．10．Amaximumadvancedglaciersnoutturnstoa glacialsnout and the tongue−Shaped debris hillfor
recent20years．The front of themain valleyglacier
Stagnant glacier snout by decreasing of the glacial
retreatedmorethanlOOmindistance，and theglaciermass．The following positive mass−balance ofglaciersurfacelowered30r40m，Whilefrontalpositionsofthe
thickenstheupperandmiddlepartsoftheglacierandtributary cone−tyPe glacier have not changelargely
increases the movement．The moving−end of thegla−
andsurfaceloweringof1520misobserved．
Cier（active snout）flowed up on the debris−free stag−
Inner slopes of the marginal higher part of thenant−ice and continued to advance．After stopping
debris hillpartlydecrease3r7minelevation andthe
advance and following retreat yielded the residual
whichleft debris as the advanced glacier snout re−treated．Thewholescenarioisschematicallyshownin

debris−mantle on the stagnant glacialtongue．Thus
the debris−free glacialsnout turned to the debris−

mantled glacier．Although such glacialadvance andOVerride followed by retreattypically occuron surg−

centrallowerpartlowered5−10m．Thedistinctsubsi−

dence occurred on the debris hill in the upper partnear the glacialfront．Cause of this subsidenceis

ablation of the underneathice，therefore the under−lwataetal．

neathice existsin the entire debris hi11．Thus the

ノウ7

ang，theXinjlangInstituteofEcologyandGeography，

debris hillin front of the glacialsnoutis a debris−
mantled glacier−SnOut Of the previous glacialstage

ChineseAcademyofScience，forsupportonthejoint

Ciersnoutandisretreatingatpresent．

COmmOdation at the Tianshan Station．

not accumulated by supraglacialmelt−Out prOCeSSeS，References

project，andtoMr．QiaoKeqin，ColdandAridRegions

rather than anice−COre mOraine．The present debris−
Environmentaland Englneering ResearchInstitute，
freeglaciersnouthascoveredthedebris，mantledgla− Chinese Academy of Science，forkind supportofac−
Thedebrison theolderdebris−mantled snout was

because contentsofenglacialdebris are very scarce．
Nogeomorphologicalchangein theglacierbasin has
occurred so that this peculiar change from the older

debris−mantledglaciertotheyoungerdebris−freegla−

Ciercannotbeexplainedbydirectdebris−SupPlyonto
the glacier．The authors conclude that the possible

CauSeOfthedebris−mantleorlginatesfrom thedebris−rich basal−icelayer of the advanced glacier．A maxi−

mumadvancedglaciersnoutturnstoastagnantgla−Benn，D．Ⅰ．and Evans，D．J．A．（1998）：Glaciers and Glaciation，
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644．
Ciersnoutbythenegativemass−balanceofglacier．In
Iwata，S．（2000）：PhotoStudioofSnowandIce（CleariceofNo．
the following positive state，glacier thickens andin−
6 Glacier，at the head of UrumqiRiver，Tian Shan）．
CreaSeS the movement．The activesnout，mOVing−end
Seppyo，62（2），irii．
Iwata，S．（2004）：Twenty years morphologicalchanges ofOf the glacier，With debris−rich basal−icelayer over，
NumberSixGlacier，UrmuqiRiver，theTienshan Moun−rideson thedebris−freestagnant−iceandcontinuesto
tains．JournalofGeography，113，430「433，advance．The preexistent debris−free glacialsnout
Iwata，S．and ChenJiyang（1987）：Data of the glaciologicaland glacio−geOmOrphologicalexpeditionin the head ofturnsto thedebris−mantled glacierafterstoppingad−

VanCeandfollowingretreatyieldstheresidualdebris−
mantleonthestagnantglacialtongue．

AcknowIedgments
Theauthorswouldliketoexpresstheirgratitude
to the Tokyo GeographicalSociety for thefinancial

SupPOrt，tODirectorZhangXiaoleiandMr．LuiWenJl−

UrumqiRiver．AnnualReportonthe Work atTianshan
GlaciologicalStation（LanzhouInstitute of Glaciology
andGeocryology，AcademiaSinica），No，3，101113．
JiZixiu（1980）：Themodernperiglacialprocessin thecentral
PartOfTianShan．JournalofGlaciologyandCryopedol−
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ShiYafeng（ed．）（2000）：Glaciers and their Environments jn
China：the Present，Past and Future，Science Press，
Beijing，410pp．