BulletinofGlaciologicalResearch19（2002）37－40 37 ⑥JapaneseSocietyofSnowandIce

Some shrinkingfeaturesin the uppermost ablation area of the Glacier，eaSt NepaJ， 1995－1999

Tsutomu KAE）OTAl，NozorTlu NAITO2and Howard CONWAY3 1Fro11tierObservatiorlalResearcbSystemforGiobalChange，317325S壬iOWa－maCbi，Ⅹa‡iaZaWa【ku，Yokobama236¶0001Japan 2GraduateSc壬100lofEnvironmentalStudies，Ⅳag野atJniversity，Fl汀0－Cho，Chikusa－k11，Nagoya4朗一8601Japan 3GeophysicsProgram，Box351650，UniversityofWashington．Seattle，WA98195USA

（ReceivedOctober5，2001；RevisedmanuscriptreceivedNovember5，2001）

Abstract

AnacceleratedsurfaceloweringoftheKhumbuGlacier，OneOfdebrisMCOVeredglaciersinthe NepalHimalayas，WaSdetectedbyrepeatedmappingsintheuppermostablationareaoftheglacier． Thesurfaceioweredatarateofal〕Out2ma001in19951999wbereasal）Otltlma▼iin1978－1995．Mean iceflowvelocitydecreasedtoabout18ma≠lin19951999fromabout26ma．1in1987－1995．Using icethicknessdata andflowvelocityin1999，annualablationovertherespectedareawasrough1y evaluatedtobeabout3．5maMl．Thisvaluewasalmostcompatibletothevalueobtainedbyin－Situ Observationinthelate1970s．Decreaseofinfluxoficefromtheupglacierwassuggestedasapossible CauSeOfrecentacceleratedsurfaceiowering．

1．1ntroduction towards the terminus．The distance from the foot of theicefallto the terminusis aboutlO km．The area Shrinkage ofthe K血umbtlGlacier frorn1978to Studiedis the tlppermOSt part Of the ablation area 1995wasreportedbyKadotagfαg．（2000）．Tbeyfotind （namedasÅreaIVbyう好atanabeぞfαg．1980）．Tbisarea that thesurfaceloweredoverallofthe ablationareai． ischaracterizedbyatransitionalchar】gefromogive GlaciologicalExpeditioninNepal（GEN）in1999con－ formtoicepinnaclerow（Fig．1）． ducted radioeCho sound－ ings and additional topo- grapbic mappingintbe ab－ 1ation area．This paper describes changesin upper－ most ablation area of the that: were Observedbythemostrecent nlaPPl11g・

2．Physicalsetting

KhumbuGlacierissitu－ atedintlleKムuInburegion， east （Fig．1）．The glacierstartsfromthebasin SurrOunded by Mt．Sagar－ matha（Mt．Everest，8848 m），Lわotse（8511m）and （7861m）．The eqt王i－ 1ibriumlineliesaround5600 m within theicefalland supraBlacial debris appears at the foot of the icefaII Witbi‡1CreaSing tbickness Fまg．1，ÅmapoftbeXhumbuGlaく鹿r，Tbelocationoftbestl三diedareaまsshown， 、淋 BulletinofGlaciologicalResearch

（a）Octokr1995

Ben（；hmark

Fig．2．MapsoftheicepinnaclezoneintheKhumbuGlacier，（a）in1995，（b）in1999． AtoDandUOtoL2denotetheicepinnaclesandpeakssurveyedrespectively，Gl andG2aregapsintheicepinnaclerow．Thescalebaraisorepresentsanabscissa Of the coordinates positive downg王acier．The origin of the coordinatesis the bencbmarkontbecresとOftberight王ateralmoraine．

3．Survey Table2．Horizontalvelocities and sudacelowering rates Obtained from the displacements of theice pinnacle C． SurveySWeremadeusingvarioustheodolitesand （period：October1995May1999） Horizontalvl Lowerlngrate electronic distance meters．Margins ofice pinnacles Position andlongitudinalridgesweresurveyedbytraversesin （ma‾1） （ma－1） Pl 17．8 1995andin1999．ResultsofmappingareshowninFig． P2 17．9 2．HorizontaldisplacementsoficepinnaclesareclearT lyseen．Atotaloffivepeaksoficepinnacleswere locatedrelatiyetothebenchmarksonthecrestofthe point．Stlrface sIope was read from a topographical rigbtlateral王nOrainebytriangulationin1996and1999 mapatascale1750000そNationalGeograp王Iic Maga－ 絆ig．2）， Zine，1988）tobe60／1000．TlleSurねcelowered atan averagerateofabotlt2ma，1between1995and1999 4．Resultsforflowandsurface暮oweringfrom1995 （Tableland2）t Figure3shows surfacelowering to1999 distributionsalongthemarginsoftheicepinnacles（a）

ウ0 ThepeaksandicepinnacleCforwhichthelongi－ ー

tudinal length remained unchanged form reliable 【 ∈ ） 粍 markers on the glacier surface and their horizontal ぎ l 盲 V i displacements can be converted to horizontalflow O l 」 O

Velocities．The resulting veloc主ties are tabtllatedin

Tableland2．Surfacelowering was evaluated by 粍 0 2∝〉 ヰ00 珊 騨 1㈱ 1200 1400 Verticaldispiacement（horizontaldisplacementxsur－ HoriヱOnt■tdist8nCe（m） face slope）and elevation change at each surveyed

盲 5 Tablel．Horizontalvelocities and surfacelowering rates ） ぎ て Obtainedfromthedisplacementsofthepeaksoficepinna・ ○ 主 0 】 Cles．（period：October1996MMay1999） 」 n

V

Horizontalvelocity Lowerlngrate

（ma【1） （ma，1） 5 0 2∝1 400 600 朗氾 1㈹0 1200 1400 U（） 日orizontaldist■nCO（m） 1

2 Fig，3．Sl汀faceioweri喝distributions during1995 1

2 －1999，（a）alongt主1eedgesoftheicepirlnaCi蕾，くb）

「 aiongtberidgesbesidetheicepinnacierov， ∴ U

L

L

Kadota g≠αJ． 39

andalongtheridgesbesidetheicepinnaclerow（b）， 2000）andsurface velocityobtainedin1999，namely The surfaccloweredby about5to9m on average 358m deep at Gl，324m deep at G2and18m aJl from1995to1999，Vhichresul捷din王oweringatarate respectively．Surface width was obtained frorn the Ofl．4to2．5ma‾10naVerage． map（NationalGeographic Magazine，1988）．‡n払e Calculation，Parabolicshapesofthecross山SeCtionand 5．Discussion andconc山dingremarks 80 ％of surface velocity for mean velocity were assumed．Notethatmassbalanceintheequationcan ゑJ．克彦ノ熟紺 be considered to be abiation rate becatlSe aCCumula＿ Sekoetal．（1998）obtainedicevelocitiesintheice tionthereisnegligible▲ pinnaclezonetlSingsateliiteimagesin1987and1995． Tbeaverageablationratein也eicepinnac‡ezone F主卯re4sbowstbelorlgitudinald圭stributio‡10faver－ obtainedby王noueandYosbida∈1980）wasO．025Ind▼ユ， ageflowspeedsintheicepinnaclezonefortheperiod Whichwasbasedontheirfieldobservation（bystake 1987r1995（after Seko et al．，1998．Fig．乱modified）， method）in whoIc of August1978．If ablation takes 1995－1999and1996】1999．Itisobviousthat幻owspeed piace wit壬Itbis ablatiorlrate OVer abiation period， basdecreased overtbeiast decade． frommid－MaytoendofSeptember（about140days）， resultingannualablationratecomes3．5ma‾1．Conse・

0

quentlyitcanbeconsideredthatablationconditionin

＜ U

（ ㌔ theicepiIlnaClezonehasnotc壬Ia王1gedsomuchsince ▲ ． ∈ U

）

で ∧ thelate1970s． U 冨

旨 ∧ 喜 U

一 S

L ． A ． ・了．∴（∴．・ごへ・：・′∴・J；－ノ／・′√＼・′申・・∴・．・・・‥－′′、・

3

， Sl汀ねcelowering resultsたom eitber decreased － 0 ¢掴 づ卸 500 l000 150D － － influxoficeorincreasedablation（orfromboth）．The

日oバヱOntaIdis也∩（；e（m） foregoingdiscussionmaysuggestthattheaccelerated Fig．1l．Thel（）ngitudin31distrihufio［1S Of thビrneall Surfaceioweri王1gilュtbeice pinnacie zone of汰e ice flovspeedsintbeice pinnacle zone of tbe Khumbu Glacier was causedby decreasedinflux of Xhumbu Glacier for the period1987－1995（thin ice．Thismayalso suggestdecrease ofmassbalance SOlidlines，afterSekoetal．，1998，mOdified），1996 －1999（thicksolidline）andfor1995－1999（dotted （decreaseinaccumulationand／orincreaseinablation） lines）．Theabsci∬a主ssameastbatinFig．2， inthe acctlml11ation area．

5．之 了切言乃刀薮噂和お（才む¢ Acknowledgments Kadotagf♂g．（2000）obtaiIledt壬1eSurfaceloweri喝 0Vertbeicepi王InaClezonebycompar主ng払eaverage l好e express our appreciation toI）epa豆me涙Of elevationsin50m x50m mesh areain the maps HydrologyandMeteorology，MinistryofScienceand preparedbythesurveysin1978andin1995．Resulting Technology，HisMajesty’sGovernmentofNepalfor averageloveringratesin1978－1995andthosein1995 tbeircooperationin（〉urreSearChin Nepal，1野e also －1999are tabulatedin Table3．It can be concluded thank an anonymous reviewer for his belpfulcom－ thatthinningoficehasaccelerated． ments toimprove the manuscript．This study was financially supportedby GrantLinAid for Scientific Table3．Mean餌rねce王0Veringraとesaio喝theiceplnnaC‡e Research（No．09041103）fromtbeMinistryofEdlエCa－ roⅥ7dur主ngぬeperiods1978－1995and1995－1999▲ tion，Science，Sports and Culture，Japanese Govern－ Leftbankside Rightbankside ment and cooperative research under the Japan-US 恒lこl‾1） （tlla■▲ll CooperativeScienceProgramfromJapanSocietyねr ’78ノ95 0．35 1．1 tbe王）romotionofScience． ’95ノ99 1．4－2．5 1．4 References ノラ．．フ‥1砧J／わ′J（甘t、J■仙、Jハー仲川r7（、ん7こ√川〔l Annualablationrateinthe areabetwecnGland Gades，A．，Conway，H．，Nereson，N．，Naito，N．andKadota，T， G2wasroughlyestimatedtobeabout3．5maMlfrom （2000）：Radio echoTSOundings throughsupraglacialdebris thefollowingcontinuityequation． On Lirung and Khumbu Glaciers，NepalHimalayas，In： Debris－－Covered Giaciers（ed．By M．Nakawo，Ct F． 」1＿J、 ・・・・り り＿：．ヽ． Raymond＆Å．Fotlntain）（Proc．SeattleWork曲op，Septem－ ber200（））．IAHSPubl．No．264，13－22． wbere∠ゴゐ／』才；thicknesscbangingrate（－2ma‾i），あ； Inot吟J．an（葺Yoshi（まa，M．（1980）：Ablatiorlandheatexc‡lamge masst〉alarlCe（ma…1），¢J；icefluxthrotlghcross－SeC衿 OVertbeKbumblユGlacier．Seppyo，Vol．41，SpecialIsslユe，26 tionatGl（m3a－り，Qβ；ice鮎Ⅹthro11ghcross欄■－SeCtion 嶋33． Kadota，T一，Seko，K．，Aoki，T．，Iwata，S．and Yamaguchi，S． atG2（m3a脚l），S；Surface area（m2）．Ice fluxeswere （2000）：ShrinkageoftheKhumbuGlacier，eaStNepalfrom Calcuiatedusingtbeまcetbicknessdata（Gades g≠αg．， 40 BulletinofGlaciologicalResearch

1978t（〉1995，In：Debris－CoveredGlaciersくed．Bぅ7MtNak－ Glacier，NepalHi‡nalayas revealed by SPOTimag缶， awo，C，F，Ra㌢nOnd＆A．Fountain）（Proc．Seattiel好ork＝ 8u11eとinofGiacierResearcb，16，33－4ユ， Shop，September2000）．IAHS王）ubi，No、264，235243． Wata－1abe，0・，Fu魂imi，H．，Ikegami，KりTa三泊ka，YヮYos出da， NationalGeographic Magazine（1988）：， M．，Iwata，S．，Inoue，J，andUpaday，B．P．（i980）：Outlineof NationalGeographicSociety，Washington，D，C． Studies on suprLaglacialdebris of the Khumbu G王acier， Seko，K．，Yabuki，H．，Nakawo，MりSakai，A．，Kadota，T．andKhumbuRegion，Seppyo，Vol．41，SpecialIssue，5L8． Yamada，Y．（1998）：Changing＄urfacefeaturesofKhumbu