79

BulletinofGlaciologicalResearch21（2004）79−90⑥JapaneseSocietyofSnowandIce

Outline of2002−reSearCh activities on gJaciers and glacierlakesin Lunana region，Bhuta

Himalayas

TomomiYAMADAl，Nozomu NAITO2，Shiro KOHSHIMA3，HirojiFUSHIMl4，Fumio NAKAZATakahiro SEGAWA3，Jun UETAKE3，RyoheiSUZUKl6，NariyukiSATO7，KARMA8，lndra
CHHETRl8，LobzangGYENDEN8，HironoriYABUKl9and Kazuhisa CHIKJTAlO
lInstituteofLowTemperatureScience，HokkaidoUniversity，SapporoO60−0819Japan

2DepartmentofEnvironmentalInformation，HiroshimaInstituteofTechnology，Hiroshima731L5193Japan
3GraduateSchoolofBioscienceandBiotechnology，TokyoInstituteofTechnology，Tokyo152L8551Japan
4SchoolofEnvironmentalScience，UniversityofShigaPrefecture，Hikone5228533Japan
5GraduateSchoolofScience，NagoyaUniversity，Nagoya464−8601Japan
6GraduateSchoolofEnvironmentalStudies，NagoyaUniversity，Nagoya464−8601Japan
7GraduateSchoolofEnvironmentalEarthScience，HokkaidoUniversity，SapporoO60−1810Japan
8GeologicalSurveyof Bhutan，P．0．Box173，Thimpu，Bhutan
9FrontierObservationalResearchSystemforGlobalChange，Yokohama236rOOOIJapanlO GraduateSchoolofScience，HokkaidoUniversity，SapporoO600810Japan（ReceivedOctober3，2003；Revisedmanuscriptreceived NovemberlO，2003）

Abstr・aCt

Forthepurposetoinvestigateformationandexpansionmechanismofamoraine−dammedglacier
lakeinconnectionwithshrinkageprocessandmechanismofaglacier，fieldobservationswerecarried

OutOnLuggeTsho（Luggeglacierlake），debris−COVeredLuggeandThorthormiGlaciers，anddebris−

freeGanjuLaGlacierintheLunanaregion，BhutanHimalayasinthelateSeptembertotheearly
October2002asthefirstyear
Bhutan．

sactivityofthethree−year−jointresearchprojectbetweenJapanand

Surveyswereperformedonthelake−basinmappingofLuggeTshoandonpositionofshorelines

Ofthedown−andup−1akeends，Whichareexpansionfrontsofthelake，forassessingexpansionprocess
andrate．Thedeepestlakedepthwasrevealedtobe126m，themeandepthtobe49．9m，andthestored
WatertObe58．3millionm3．ThethermalanddensitystructureofLuggeTshowerealsorevealedusingaTTDProfiler．Thedischargeanddailyrunofffromthelakewatershedof54．2km2wereclarified
tovaryfrom2．5to5m3s￣1andfrom4．3to6．8mm，reSpeCtively．
ThesurfacetopographiesofLuggeandThorthormiGlaciersweresurveyed，tOO，ineachablation
areafordetectingsurfacelowering，Whichcouldcontrolformationofglacierlake．Thetotalof31
stakeswere embeddedinthe areas to measure surface massbalance andflow．

A50cmdepthpitobservationanda614cmdepthcoredrillingwereperformedonGanju La

Glacier．Thesamplesarebeinganalyzedbyvariousdatingmethodstoclarifyannualnetaccumula−tion．

The outline ofthefield activitiescarried outin2002isreportedwith the preliminaryresults
Obtainedalsobytheotherobservations．

1．lntroduction

Sufferingthestronginfluenceofthesummermonsoo11（Karma et al．，2003）．

Glaciers in the world tend to shrink under the

influence oftherecentglobalwarming．Thetrendis
especially clear andhas acceleratedin a recent few

The glaciers mainly consist of smalldebris−frecglaciers andlarge debris−COVered glaciersin thc

Himalayas．AsthedebrisTCOVeredglaciersareshrunk，
decadesintheGreatHimalayas（Yamadaetal．，1992； many moraine−dammedglacierlakes have appeared
Agetaetal．，2001）becausetheHimalayanglaciersare On their debris−COVered ablation areas．The newly
SummeraCCumulationtype（AgetaandKadota，1992）． bornlakes have frequently caused glacierlake out−
Itis conceivable that glacier shrinkagein Bhutan
burst floods（GLOFs）in this half centuryin thc
WOuld be especiallylargein the Himalayas due toHimalayan countries of Bhutan，Nepal，India andBu11etin ofGlacioIogicalResearch

β0China（Yamada，1998）．GLOFinflicted serious dam−ages not only to humanlosses，the valuableinfras−

tructure and foundation ofvi11agers，but also to thefragi1enaturealongtheriver．InBhutan，GLOFshave

happenedatleastfourtimessince1950，mOStreCently
in1994，the Lugge Tshoburstintheeastern Lunana
region．GLOFmitigationisnowurgentissueinthese
COuntriesfortheireconomicaldevelopment，andalso
forvi11agersandfragi1eHimalayannatures．
To find adequate measures of GLOF mitigation
mustbedifficultwithoutenoughknowledgeonmech−
anlsmsofthelakeformation，andofastonishinglaketeams．The first team，COnSisting of 7Japanese（Yamada，Naito，Nakazawa，Segawa，Uetake，Suzuki，and Sato），and3 Bhutanese，Karma，Chhetri，andGyenden，1eftThimpuon26Augustandarrivedatthe
researchsiteinLuggeTshoarea，theeasternLunana
On14 September．The second team consisting ofKohshima，Fushimiand Ushida（Kyoto Prefectual

University）1eftThimpuon6Septemberandjoinedthe
firstteam on23September．
Duetounfortunate transportationproblems，theproposed2002research plan was forced to change
COmpletely，and the start of fuilresearch activities

expansion，and characteristics of GLOFitself．To WaS delayed to21September．In addition，the Nika
Chhuroute，Whichhadbeenplannedtouseasarela−investigate behaviors of the past GLOF events andrisk assessment of each moraine−dammedlake arealsoimportantforevaluatingafutureGLOFpossibil−
ity and damages along a GLOF running river．
Monitoringofvariationsofglacierlakesisalsoneces−

Sary．Inaddition，amaSSbalancestudyshouldbemade

tivelyshortreturnroutefromThanzatoThimpu，WaS
Closed due to spread of foot and mouth disease ofYaks．The relativelylong SnowmanTrek Route，On

WhichwecametoLunana，Shouldbeagainemployed

as the return route．Accordingly，the duration ofresearchactivitiesintheLuggeareawerelimitedfor
astheessentialbackgroundofglacierlakeformation，Only two weeks from21September to50ctober，because glacier lakes are born on the shrinking
Shortenlng about two weeks from the proposed
processes of debrisTCOVered glaciers．Sinceitis too
difficult to perform such studies on debris−COVered researchplan．
Debris−free glacier research party（Kohshima，
glaciers due to theirlarge size and difficultyin ap−

proachingtheiraccumulationareas，Smalldebris−freeNakazawa，Segawa，KarmaandLobzang）1eftBCfor

glaciershouldbestudiedforunderstandingthetrend
Ofglaciermassbalance．Itis also advantage for the
massbalancestudythatasmallglacierwouldquickly
respondtoclimatechanges．
In this connection，theJOint research project
betweenJapan and Bhutan（GeologicalSurvey of

Bhutan，GSB）was conductedin1998（Ageta and
Iwata，1999）and1999toinvestigateabovementioned
issues．For continulng the studyintensively，three−year−joint research project during 2002−2004 was

GanjuLaareaon30SeptemberandarrivedatGanju
La Glacier on 3 0ctober．The other 8 members

COntinuedresearchactivitiesintheLuggearea．Intheproposalplan，debris−free glaciersinJichu Dramo

area on the way to Nika Chhu were planned to beinvestigated．However，aS nO tranSpOrtation wasavailable to approach there，the research area fordebris−freeglaciershadtobechangedtotheGanjuLa

area．Theresearchperiodforthe debris−freeglacierplanedandlaunchedintheautumnof2002．
Thisreportdescribestheoutlineandsomeprelim−
inaryresults ofthe field activities performed on thefirstyear ofthe20022004project．

WaSalsoforcedtobeshortento3daysonly，from4to60ctober．TheLuggepartyleftBCon60ctoberandjoined the Ganju La party at Woche on the way toThimpu on80ctober．Allmembers were back at
Thimpu on170ctober．

2．Research areas，members and schedule

3．MeteorologlCalobservation

The research project was carried out in the
Lunanaregion of Bhutan HimalayasbylOJapanese
and3Bhutanese members from September to Octo−

WaSinstalledin the deadice area，1ying between

ber，2002．Thetrekkingrouteandtheresearchareas
areshowninFig．1．Amoraine−dammedglacierlake，
Lugge Tsho（Lugge Lake），and two debris−COVeredglaciers，LuggeGlacierandThorthormiGlacierwere
investigatedin the eastern Lunana near Thanza vil−lage．Six debris−COVered glaciers and two well−developed glacierlakes are distributedin this area

（Fig．2）．A debris−freeglacier wasinvestigated on
Ganju La Glacier（tentative name）locatedin the
GanjuLa（Ganjupass）nearWochevillage，thesouth−
western Lunana（Fig．1）．
The research members were dividedinto two

An Automatic Weather Station（Lugge AWS）

LuggeTshoandtheendmoraineofLuggeGlacier（●
inFig．2）．

Its altitudeis4566m，referred to the BC bench−

markaltitudeof4550ma．s．l．Thetotalof9meteoro−

loglCalcomponentswere startedto record automati−

Callyat12：000n17September，2002；airtemperature，
relative humidity，preCipitation，Wind speed，Wind
direction，downwardandupwardshortwaveradiation，

andnetradiationarerecordedevery30minutes，andgroundsurfacetemperatureisrecordedeverylhour．
In addition，the maximum snow depth gauge wasinstalled to obtain the maximum snow depth in thewinter2002／2003．

Yamada et al．

Fig．1．Trekkingroute（thickdashedline）andresearchareas（squaredareas）．Thin
dottedlinesareotherexistingtrekkingroutes．

Fig2．Distribution of glaciers and glacierlakesin the eastern Lunana，Bhutan
Himalayas．（Thebasedsatelliteimagewastakenon20Novリ2001，byASTERSenSOr・）ThesymboIsindicateasfollowing；▲：BC，●：LuggeAWS，◎：Precipita−
tiongauges，◆：HydrologicalStation，★：Waterlevelsurveyedpointsofsupra−
glacialpondsonThorthormiGlacier，＿：Benchmark fortopographicalsurvey．

Stakeswereinstalledintheenclosed areasbythick dashedlinesonLuggeandThorthormiGlaciers，aI−dsurfacetopographiesoftheglacierswerealsosurveyed
in the areas．On the surface of debris．covered ablation area of Thorthormi

Glacier，thereexistmanysupra−glacialponds．Theabove−mentionedwaterlevel
SurVeyedpoints（★）areatedgesoftwowellAdevelopedponds，Whichareslenderly
locatedalongtheleftlateralmoraine．

βJ

＆2

Bulletin of Glaciological Research

The temporal variations of the meteorological
COmpOnentSduringourstayinthefielduntilll：000n

mapofl／50，000．Atthetwosites，themaximumsnow

theformerperiod，aSitcanbeseeninthevariations

Austrian andGSB．After obtainingone year datain
2003 autumn，distribution of precipitation willbe
revealedonaltitudeandalongPhoChhurivervalley
byutilizingalltheavailabledata．

depthgaugeandthetotalprecipitationgaugearealso

60ctober are shownin Fig．3．Totalprecipitation installed．Infact，theprecipitationhasbeenautomati−
duringthe19dayswas42．6mm．WeatherwasbadinCally observed also at Thanza by the joint team of
Of precipitation（Fig．3（b）），air and ground surface
temperature（Fig．3（a）），andshortwaveradiation（Fig．
3（d））．Therelativehumiditywasgenerallyhigh（Fig．
3（b））．Thevariations ofwind speed and directionin
Fig．3（c）indicateexistenceofmoun−tainandvalleywindssysteminthis

area；relativelystrongwindindirec− 回

tionofNW，Whichcoincideswiththevalleyaxis，（valleywind）indaytime
and weak wind（mountainwind）innight．Suchwindsystemistypicalinmonsoon season in the Himalayan

regions（Inoue，1976）．The radiation
COmpOnentSinFig．3（d）areshownas

︵
0
0
︶
巴
コ
ー
空
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∈
β

20

1 0

0

∩

positive when those heat flow−VO

toward the ground surface．The al−

︵
辞
︶
倉
p
盲
⊃

bedo was evaluated to be O．17 0n

average at this Lugge AWS site，
where the surface is covered by
Sand．Longwave radiations are notdirectlymeasured．The upwardlon−

gwave radiation can be calculatedwith the ground surface tempera−ture，andthedownwardonecouldbe

1 O

O
l

8

eration with GSB．

Precipitationisoneofthemost
important meteorological compo‑

nents for the studies above−

mentioned；itis known to depend
StrOnglyonaltitudeandlocaltopog−

raphy．Therefore，additionaltwo

tipping−bucket precipitation gauges

wereinstalledin different altitudes

around Lugge Tsho area as shown

byOinFig．2．Oneisbesideabench−

mark for topographical survey on
theridgeofrightlateralmoraineof
Lugge Glacier，altitude of whichis
about4660m according to a handy

GPS；theotherisonapeakatnorth−wardofBC，altitudeofwhichis5043
masdescribedonthetopographical

0 5

6
0
3

4

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∈
︶
旦
s
p
屋
≦

mass baユance study of glaciers andalsothestudyofanexpansionmech−anismofglacierlakesinthisreglOn．
ThisLuggeAWSsystemisplanned
tomaintainforalongtermincoop−

1

O

聖
篭
一
〇
∝

estimated as the residualterminradiationbudget．
Themeteorologicaldataduring
lfullyear willbe obtainedin2003
autumn．They could contribute to

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ち
0
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寸

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b

Fig．3．TemporalvariationofeachmeteorologlCalelementrecordedatLuggeAWS
during19daysin2002autumn．Recordingintervalis30minutesforallelements
exceptgroundtemperature，theintervalofwhichislhour．（a）Airtemperature（thickline）andgroundsurfacetemperature（thinline）．（b）Relativehumidity（1ineforleft axis）andprecipitation（barforrightaxis）．（c）Windspeed（1ineforleftaxis）andwinddirection（crosssymbol，×forrightaxis）．（d）Netradiation（thickline），downward（upperthinIine）andupward（lowerthinline）shortwave radia−
tion．Signispositivewhenheatflowstowardthegroundsurface．

Yamada et al．

4．Observation of Lugge Tsho
Lugge Tshois one of the typicalmoraine−
dammed glacierlakes in the Bhutan Himalayas．
Thoughthelake once released quantities oflake
Waterin1994，therisk offutureGLOFremainshighSincethelakestillstoredenoughamountofwater，and
themorainedamwasnotyetcompletelycollapsed．
As the basic information for the risk assessment
OffutureGLOF，thecharacteristicsoftheLuggeTsho
Wereinvestigated．

∫■7

The deepest depth of126m appears near theterminusoftheLuggeGlacierandtheaveragedepth

is 49．9 m．Thelake area and the stored waterisrough1y estimated to bel17ha and58．3million m3，
respectively．Thus，although the Lugge Tsho has

alreadygeneratedaGLOFin1994，thelakestillstoresabundant water enough to generate another GLOF
again．A continuous attention should be paid oIlmonitoringchangesofmoraine−damaroundtheoutlet
OfLuggeTsho．
／．二 11−ノ／■r／．J′小ノ一丁／／仙 ′〃ハ／／／／ノ付−／巾／リ・叫・J．J．し、（りけむ／…／J／り〃（リ￣仙・ん山一んバJJJ

To understand the configuration of the Lugge
Tshobasin，thedepthsofthelakeweremeasuredby
a measure tape with a weight from a hand−rOWlng
rubberboat．Themeasurementwasmadeat70points

In order toinvestigate the thermaland density
StruCtureS Of Lugge Tsho，the verticalprofiles ofWater temperature（T，OC）and turbidity（ppm）were

measuredon29SeptemberbyaTTDProfiler（Model：

ATU200）at4pointsshownby●inFig．4．Thewater

during4daysfrom25to28September．Themeasure− temperatureprofilesarealsoallowedtoestimatethe

ment points were surveyed using a differential GPS
SyStemandalaserdistancemeterasanauxiliary．
ThebathymetricmapoftheLuggeTshoisshown

Changeofstoredheatinthelake，Whichisoneofthe
importanttermsforassessingheatbudgetofthelake．
Verticalprofiles of water temperature，SuSpended

1ite and alaser distance meter which willbe

frommeasuredvaluebyusingarelationship，Whichis

inFig．4．Thepositionsofthedown−1akeshoreandthe Sediment concentration（SSC），and calculated bulk
up−1akeshorearesurveyedbyusingadigitaltheodo・ density o・areshowninFig．5．The SSCisconverted
mentionedlater．Bothlateralsides of thelake were

determinedbythedistancebetweentheboatposition
andthe shore oftheleft and rightlateralmoraines，

describedinFig．40fChikita et al．（1999）．

Sincelake waterincludes fine suspended partiq

Cles，densityofwhich（SD）is assumedtobe2730kg
withthehelpofatopographicalmap（1：50，000）anda m3，anditsbulk density（BD）ishigherthanthatof
Satelliteimagery taken on19September2002．The
purewater（IW）ascalculatedbythefollowingequa−boat position was measured by the differential GPS
SyStemandthedistancebetweentheboatandboththeshores of the moraines was measured by the laser
distancemeterwithaccuracyoflm．

tions：β∂＝（1−SSC／S∂）×lγD＋且SC，■8MO
B且沈Camp
AWS●

Ioedi仔Lug騨Gl血r

Fig．4．BathymetricmapofLuggeTsho．Smallfiguresinthemaprepresentdepths
Ofthelakemeasuredattheirsurveyedpoints，theunitofwhichismeter．

（1）BulletinofGlaciologicalResearch

β4lγD＝1000×（1−（r＋288．9414）×（T−3．9863）2／（508929．2／（r＋68．12963））），（2）where Tiswatertemperature（OC）．TheEq，2is anempiricalequation called as the Thiesen−Scheel−

Diesselhorstequation（Maidment，1993）・SinceBDis
nearlyequaltolOOOkgm￣3，thedensitylSrepreSented
bythedeviation，0・，definedbyo・＝（BD−1000）×10・

Thelake wateris characterized by extremely

richsuspendedsedimentmorethanO．3gL￣1inconcen−

tration．TheconcentrationprofileofsiteTTD3shows
WalorTemp￠ratl∬e（℃）or8（k如3）

Wal町丁餌np訂慮We（℃）0川（kさ血3）
0 1

2 3 4 5 6 7 8 9

0 1 2 3 4 5 6 7

8

9

0

10
20
30
40
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6
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き

0

5

0

′
0 0
0

7
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▲
．
．
8

9

0．0 0．1 0．2 0．3 0．4 0．5 0．6 0．7 0．8 0．9

S岨pendedSedimcntConcentration（〆L）

WaterTcmpcraltqe（℃）orq（k如13）

WderTemperatl−e（℃）oro（kgm3）

0 1 2 3 4 5 6 7 8 9

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占
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り
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5

0．0 0．1 0．2 0，3 0．4 0．5 0．6 0．7 0・8 0・9SLBpendedSedimentConcentraIion（gL）

0 1 2 3 4 5 6 7

8

0

0

′
○

0．0 0．1 0．2 0．3 0．4 0．5 0．6 0．7 0．8 0．9 0．0 0・1 0．2 0・3 0・4 0・5 0t6 0・7 0・8 0・9SuspendedSedimentConcentration（dL）

餌叩endedSedimentConcentration（釘L）

Fig．5．Profilesofwatertemperature，SuSpendedsedimentconcentration（SSC）andbulkdensity（0．）．

9＆5

Yamada et al．

relativelyhighSSCintheintermediatelayerof30to70mindepth．Thethicknessofthisintermediatelayer

gradua11y decreases from up・1ake to down−1ake as

Seen from site TTD4to TTD6．This suggests thehorizontalintrusion of suspensioninterflow from

SiteTTD3toTTD6．Thebottomlayerofthelakeat
Site TTD3 near theglacier terminusis obviously
OCCupiedbytherelativelycoldandhighturbidwater
atmorethan95mindepth．ThesecharacteristicSSC
profiles are attributed to two main waters flowing

8／22 1／24 8／21 0／28 0／30 10／2 10／1 10′l
︵
∈
○

0

○
＞
○
こ
○
盲
蓼
●
l
コ
ー
O
j
V

intothelake．Oneissupra−glacialstreamwaterfrom

Drukchung Glacier via Lugge Glacier surface．The
Streammaymainlyflowintotheintermediatelayerof
Lugge Tsho．The otheris watercomingthroughthe
enTglacialdrainagesystemofLuggeGlacier，Whichis
Characterized by relatively cold and sediment rich
Water．Thewaterdirectlyflowsintothelakefromthe
en−glacialchannelorchannelsopenlngunderwateronthelake・Sided slope under theice cliff．The water

creates the cold and sediment rich layer seen justabove the bottom of site TTD3．Thisindicates that

5
■
V5
︳
q
■0
V
■
■Fig．6．Temporalvariationofabsolutewaterlevel．
︺

andthe60％depthflowvelocitymeasuredeachatlO
Verticalsectionsalongatransversalcrosssection，theSurfacewidthofwhichwas980cm，attheoutletsite．

Therelationshipbetweentheabsolutewaterlevel（theverticaldistancefromthewater surfacetothewaterlevelBenchmark）andthedischargeisshowninFig．7．

Using the relationship，the automatically measured
waterlevelisconvertedintothedischarge．Temporal

theinflowwatergeneratedthesediment−1adenunder− VariationoftheresulteddischargeisshowninFig．8．
flowonthedown−1akeslopeoftheglacier．
Theamountofdischargeisvariedfrom2．5to5m3s￣1

Water temperature falls in relatively narrow
rangebetween2and3OCthroughoutthedepth，eXCept
for the bottomlayer at site TTD3，and thereis no
WarmWaterinthesurfacelayer，SuggeStingnoactive
Warmingbyradiationinthisseason．
Thedensityprofilesindicatethatthelakegener−
allystandsinthestabledensitystratification，thoughmany unstablelayers are seenintheintermediate
layersduetohorizontalintrusionofrelativelyturbid
Wateratmanydepths．

in this season．In the fine weather beginnlng Onl
October，thedischargeremarkablyincreasesupto5

m3s￣1．Thedailydischargefromtheareaof54．2km2，
derived from thel／50，000 topographicalmap，isVariedfrom230，500to369，800m3dayLl，Whichcorre−
SpOndstodailyrunofffrom4．3to6．8mm．

︵
●
＼
巾
∈
︶
O
u
L
ヱ
￡
岩

J．JJ抽（、ん（JJ甘サ（り〃山隼粁71／Jり〃・〝／りT／J（▼（JToinvestigatehydrologicalfeaturesoftheLugge
WaterShed，Waterlevelanddischargeweremeasured
attheoutletofthelakeandtherelationshipbetween
them was obtained．The HydrologicalStationis

4
4
3
∧
■

■
ヽ
V
O

■
■
■

Shownby◆（HS）inFig．4．

Therelativewaterlevelwasautomaticallymea−
Suredwithlhourintervalfrom14：000n23September
to12：300n50ctoberbyahydrostaticpressuretype
Waterlevelgauge．Thegaugeisstilloperatingandl
yearlong datawi1lobtainedin the autumn of2003．
The relative waterlevelmeasured by the gaugeis
COnVertedintoabsolutewaterlevelbyreferringtoa

fixedpoint（Water LevelBenchmark）on a bigrock

nearthesite．Thefixedpointconsistsofasteelbolt
embeddedintotherock．Thetemporalvariationofthe

absolute waterlevelisshownin Fig．6．Waterlevelslightly decreased with time during September andremarkablyincreased in October．A typicalpost
monsoonclimatebeganandfinedayscontinuedfrom
lOctober．Waterlevelonlychangedwithin20cmin
theobservationperiodof12days．
Thedischargewascalculatedbythewaterdepth

0

15

50

55

80

Ab00lut●W■t■rL●Y●l（￠m）

15

Fig．7．Relationship between absolute waterlevelanddischarge．

︵
て
︻
∈
︶
●
巴
¶
エ
︒
中
古

5

▲
﹁

3

9／22 0／之I l／28 1／28 9／30 10／2 1（け1 10／8
Fig．8．Temporalvariationofdischarge・

Bul］etinofGlaciologjcalRe5earCh、ヾ†；

5．Observation ofdebris・COVered glaciers珊

Thoughsix debris−COVered glaciers are concen−

瑚

tratedintheLuggearea，0nlyLuggeandRaphsthreng
Glaciers have welldeveloped moraineTdammedgla−

︷
∈
︶
O
P
⊃
l
芸
V

Cierlakes on their ablation areas（see Fig．2）．As

mentionedintheintroduction，Lugge Tshohad once
burstin1994．Itis stiilevaluated as very dangerous

嘲嘲嘲（AgetaandIwata，1999）becausethelakestillstored

abundantvolumeofwaterbehindthemoraine．Among

theotherglacierswithnobiglake，ThorthormiGla−
Cierhasmanysupra，glacialpondsonitsablationarea．

＿600

−300

Sincethosepondsaregrowingaccordingtotheinspec−tion of satelliteimaginaries takenin different years（Agetaetal．，2000）thesupra−glacialpondsareconsid−
eredtobedevelopinginto onemoraine−dammedgla−

Cierlake by means of enlargement of ponds andCOnneCtingtoeachother．Amoraine−dammedglacier

lakeisnowgraduallyformlrlgOnThorthormiGlacier．
Therefore，LuggeGlacierandThorthormiGlacierare
Chosenas the typicalglaciers，alreadyhavingalake

andundertheprocessoflakeformation，reSpeCtively．

300

0

900

608

R01ativ010ng軋Id事nald18也nco（m）（b）●

ム●△簾 △●。
．△食料× △

4510

△×

○
●t】4500
コ

×

△ ●△
A

ム ● ××）●糾98

Once alake has formed，it expandsinunbelievably

highrate（Yamada，1998）．LuggeGlacierisinvestigat−
ed as atypicalsampleinthis stage．Meanwhile，theformationofaglacierlakeessentiallydependsonthe
rateofsurfacelowering，Whichdependsonthesurface

massbalanceandtheemergencevelocity，i．eリthicken−

1ngrateOfaglacierduetocompressiveflowusuallyrealizedin the ablation area（Yamada et al．，2003）．

These observations were planed to carry out on
ThorthormiGlacier．

−1000

ー500

D

500

1000

Rotativotongttudinaldl＄bnco（m）

Fig．9．Surface topography along thelongitudina11ine of（a）Lugge Glacier and（b）ThorthormiGlacier．The
relativelongitudinaldistance refers to the cross pointwith the transversalsurveyline as positive to up−
Stream．

located at distance of about500m from theice cliff．

Similarlyitisveryriskytoapproachtodownstream
part of the ablation area of Thorthormi Glacierbecauseofmanypondsdevelopingthere．
Inordertomeasuredistributionsofsurfacemass
Ogives are well developed on upper part of thebalanceandflowvelocity，21stakes（about3．5mlong
ablation area below anicefallofThorthormiGlacier．
bamboo poles）andlO stakes wereinstalled on the
DenselysurveyedpointsaroundOto400minrelativedebris−COVered ablation areas of ThorthormiandJ．ノ．5由ゑgざgJめ材

LuggeGlaciers，reSpeCtively、Thestakeswerelocated longitudinaldistanceinFig．9（b）weresurveyedtops（△）andbottoms（×）oftheogivewaves．Theheightof

alongalongitudinallineandatransversallineoneachglacier，Their positions were allsurveyed using a
digitaltheodoliteandalaserdistancemeterfromthe

networkofbenchmarks，andtheywillbere・SurVeyed

in2003autumn．
5．2．7め（材柁ゆゐグc（ZJs〟γ〃砂〆g／αCfeγSαタカcg

ThesurfacetopographiesofLuggeandThorthor−
miGlaciers were surveyed，in addition to the stake
points，intheareasenclosedbythick dashedlinesineach ogive and the horizontalintervalof the ogive

WaVeSareabout2−3mand40m，reSpeCtively．Since

theoglVeSareformedduetoaseasonalfluctuationof
glacierflow，theirhorizontalintervalssuggestannual

flow speeds，aSSuming steady state of glacier flow．

Surface flow speed of Thorthormi Glacier would beroughly40ma1in the upper ablation area，eXaCt
Valueofwhichwillbeobtainedafterre−SurVeyOfthe

Stakesin2003autumn．

The surface flow speed（Us）should consist of
Fig．2．Theircross−SeCtionalprofilesalongalongitudi−
na11ine are showninFig．9（a）and（b），reSpeCtively． plasticdeformation（Lh）andbasalflow（Lib）．Theこら
After re−SurVeyin2003，the annualsurfacelowering depends onice thickness，Surfaceslope，ice tempera−ture，and transversalcross−SeCtionalshape as re−
willbe revealed．
presentedbyafollowlngequation：
The positions of theice cliff，Which willbe de−SCribedlater，arealsoshownby＋inFig．9（a）．Since

approachingneartheicecliffisdangerous，themost
downstream surveyed point on the Lugge Glacier is

抜＝（加sin珊4，（3）

Yamada et al．

〜？7

WhereAisafunctionoficetemperature，fisafactor
dependingonaratioofglacierwidthtoicethickness

nectssupra−glacialponds，itwi11acceleratetheshrinlく−
ageoftheglacierasSakaietal．（2000）wassuggested．
inasimplesense，Pisicedensity，gisagravitational Therefore，itisimportantforstudyofglaciershrinl（−

acceleration，αisasurfaceslope，andHisicethick− agetoinspecthowmanyen−glacialconduitsexistandness．Ifignoring Lh，Hiscalculatedtobeabout490m Which ponds areconnected each other．For this pur−byusingEq．3undergiving thたUs記40ma1，A＝pose，Waterlevels were surveyed on the two we11
6．8×10￣24s1PaL3foricetemperatureofOOC，α＝12
developed ponds along theleftlateralmoraine．The
m／400m＝0．03（seeFig．9（b）），andassumingf＝0．7．
SurVeyed points are shown by★in Fig．2．As the
However，because this probably not negligiblein
result，thewaterlevelofthedownstreampondwas3
ThorthormiGlacier，the calculated value of490m
Cmlowerthanthatoftheupstreampond．Becausethe
might be a veryweak referentialvalue as the maxi−
differenceof3cmistoosmallconsideringsurveylng
mum estimate ofice thickness．Ice thicknessis basi− accuracy，thewaterlevelsofthesetwopondsshould
Callyimportantinformation to consider glacierberatherconcludedtohavenosignificantdifference．

dynamics by means of any kind of glacier flow
models．Itsmeasurementisnecessarilydesiredinnear

futuretorevealtheformationmechanismofaglacierlake．

．う．．■ブ．ゴJ…・り・（そ／■／ノ汀∫J‖ハイ／机、∫（／／仙、rJ州ソト山ん 、ト〃（／〟…／ イ／／／／＝†♪一山Å・t−√〃（／（そ／■ナノノ（掛一穴／JりTheshorelineofthedown−lakeendwassurveyed

In other words，there must be an en−glacialconduit

COnneCting the two ponds，and the two ponds might
jointogetherinnearfuture．
In addition to above mentioned research works，
microorganisms affecting the surface albedo of theglacierweresampledatmanypointsontheablation
areasofLuggeandThorthormiGlaciers．

at68points．Theup−1akeend，Whereistheicecliffof 6．Origjninspection of water sprang out from thethe Lugge Glacier terminus contacting with Lugge

Tsho，WaS SurVeyed at ten points，COnSisting of6

leftlateralmoraine of ThorthormiGlacierpointsattopsofthecliffand4pointsattheshoreline
Of the cliff，by using the digitaltheodolite and theWaterssprangout atmanyplacesintheoutsideof theleftlateralmoraine of ThorthormiGlacier tolaserdistancemeter．TheresultsareshowninFig．4
therightbankoftheriverPhoChhu．Arethewaters
andFig．9（a）．Re−SurVeyin2003willrevealhowmuch Originated from the pond waters scattered on thc
Lugge Tsho would expand（maybeimpossible toablationareaofThorthormiGlacier？Ifthewatersare
retreat）．
leakage from the ponds，theleft moraine willbc
Thealtitudedifferencesbetweenthetopandthe
deterioratedandtendtocollapseeasilyinfuture．For
ShorelineoftheicecliffinFig．9（a）indicateheightsof inspectinganorlglnOfthesewater・S，electric conduc−theclifffromthelakesurface．Theminimumheighttivity（EC）and water temperature（7L）were mea−

・・．J．tt′′い1J・／、．，い．．l・：′＼叶ハリ心・高／′㌦り／′／、．り／

SuCh as theleakage−Water from a pond−Water On
ThorthormiGlacier，underflow ofthe river−Water Of

WaS16．2m，themaximumwas31．7m，andtheaverage
Suredat12points alongthe rightbank ofPho Chhu．
wasinbetween20L30m．Thealtitudeofthelakelevel
The EC value was automatically converted to the
WaSSurVeyedtobe4538．7minaverageintherefer− Valueattemperatureof250CbytheEC meter．
encetothealtitudeofBCbenchmark，4550m．
Thewaterspossiblyoriginatefromthreesources

77／（りイんり川〜／（；山（、ん−J・

Thoughabigglacierlakehasneverbeenformed

OnThorthormiGlacier，manySupra−glacialpondsare
distributed（Fig．2）．Amongthem，thethreepondsare

relativelywelldeveloped．Themostdevelopedpondis
located along the rightlateralmoraine，and many
icebergs are floating on the pond．The other two
developed ponds are slenderlylocated along theleft
lateralmoraine．Theleftlateralmoraine ridgeis
erodedfrombothsides；bywaterofthetwopondsat
theinner side andbythe river stream of Pho Chhu，
includingaGLOFeventhappenedin1994，attheouterSide．Becausethisridgeisverysharp，therehasbeen

a doubt that some water mightleak from theinner
ponds through the moraine and it could weaken
Strengthofthemoraine．Thistopicisdiscussedinthe
followingsection．
On the other hand，if an en−glacialconduit con−

PhoChhuandagroundwater．ThevaluesofEC and
Twofthepond−WaterOnThorthormiGlacierdirectly
COntaCting with theleftlateralmoraine were mea−

Sured，Obtaining5．05JLSm1andO、7OC．Those ofthe
Outlet−WaterfromThorthormiGlacierwas5．15JLSm−1
and3．4OC．Pho Chhu water was measured at many
pointsalongtheriver，Obtaining3．80〜3．95／JSmLland
3．3〜3．6OC．SincethevalueofECisdistinctlydiffer
entbetweenwatersfromtheThorthormiGlacier andfromthePhoChhu，theorlglnOfwaterssprangwould
beinspectedbymeasuringEC．Thevalueof7Lalso
Can be used as a reference．

ThedatasuggestthatthewaterssprangoutatlO
polntS eXCept that at 2 points near the outlet ofThorthormiGlacier are originated from the under−
flowsofPhoChhu，becausetheirvaluesofECand7L
are clearly fallen within those ranges of the river−
Water Of Pho Chhu．Evenif possible change of EC

BuIletinofGlacioJogicalResearch．ヾバfromthat ofthepond−Water duringleakagethroughおmoraineis takeninto consideration，the EC shouldhavenaturallyincreasedinthiscase，butourmeasure−mentresultsatthelOpointswerelowerenoughthan

thatofthepond・Water．Ontheotherhand，Waterata

pointsprangoutneartheoutletisobviouslyidentified
asseepagesoftheoutletwater，becausethevalueof
ECis the same as that of the pond−Water and the

∬
︵
p
︶
巴
⊃
l
巴
O
d
∈
β

器
加
1
5
1
0

outlet−Water．Then，Water attheotherpointnearthe

outletisidentifiedasagroundwaterduetoextremely

28−Sep27−S印28−S印29−S叩30−Sepl・・伽
2・0 3−−Od二5highECvalueof12．7FLSm−1incomparisonwiththoseof the river−Water，the pond，Water and the outlet−

馳toく狐）2）0
Fig．10．Experimentofsurfacegroundtemperaturebyusing
blackandwhitevinyltapesatBCfrom26Septemberto
30ctober．

Water．

As a result，nOleakage was fortunately foundfromtheThorthormiGlacierthroughtheleftlateralmoraine．Thus，thereis no apprehension of moraine 1arge amount of debris，Which forms debris−COVereddeteriorationduetoleakage．

glaciers，and moreover，there would be a possibility

thatthefallingofhugedebriscouldtriggerGLOFs．

7．Groundtemperatureobservation∴ユ（ご川〝JJ（／／川岬＝招／什＝●JJ川州／／〃ビゴ

TheHimalayanglaciersarerapidlymeltingpos−∴J．丘l♪りイ川√〃／（リ▲（／／J′川rJ／（イJ 川〟l− 〃− …止 ∫町巾、l−Jぐ〃小り†J／…

Siblybytheglobalwarming（FushimiandOhata，1980；
Yamada et al．，1992；Ageta et al．，2001）．Similarly，−

According to the GLOFs of Mjngbo Glacier in1977（Fushimiet alり1985）andLangmocheGlacierin

1985，debris falls as wellas avalanches are possible
triggerstocauseGLOFincasethat thereis a steep

melting of a permafrost layer enfeebles hardness orStrength oftheglacialmorainestructure，andwould

CauSe GLOFs．So，itisimportant to measure therockwalljustbehindaglacierlake．Ifdiurnaltemper− groundtemperatureinthemorainesinordertocheckexistenceofthepermafrostlayer andtomonitorits
aturechangeintherockwallsurfaceislarge，erOSion

processatthewallwouldbeenhanceddueto active

Change．Thepreliminaryresultsofthegroundtemper−

surface temperature．At higher altitude in the
Himalayas，blacklichens often cover rocky surface
around accumulation areas oflarge glaciersin theCOuldbeguessedthattherewouldbepermafrostlayer
in deeper part at the altitude of5239min the upper

play animportantrolebothto thelocalclimate andminthemoraineofThorthormiGlacier（（9）is，howTfreeze−thawprocess，andlargerdebrisfa11ingcouldbeature measurement at 5 points around Tempete，
LuggeandThorthormiGlaciersareshowninFig．11．
happened（Gardner，1992）．Inthisviewpoint，itmaybe
Themeasurementswerecarriedouton29September，
important to examine the diurnal change of rock
1and20ctober．From the temperature gradient，it

Himalayas．Itwouldabsorbthesolarradiationeffec− part ofTempeteGlacier，but the temperature gradi−
entsin the other4cases become smaller with depth
tively，CauSingtheupwardairmass，andformingthe
cumuluscloud alon史thesouthernslope．Inshort，the anditis difficult to judge existence of permafrost
there．Thetemperatureprofileatthealtitudeof4570
diurnalchangeoftherocksurfacetemperaturecould
theweatheringprocess．

A preliminary experiment of the rock surface
temperatureWaSCarriedoutatBCfrom26September
to30ctober by using temperature SenSOrS Wrapped

150with black and white vlnyltapes，eaCh．The former

period of the experiment was ralny from26to30
Septemberandthelaterwasfinefromlto40ctober．
FigurelOis the result，Showing that the maximum
Surface temperature with black tape exceeded more

加
︵
∈
U
︶
≦
d
￠
凸

than30OC，butthatwithwhitetapewasaround200C．

Ontheotherhand，thereisnosignifcantdifferencein

theminimumtemperaturesaroundOOC．Asthisexper−

imentairesult suggests，the blacklichenswi11maketherocksurfacetemperaturewarmerduringdaytime
andwi11influencetheactiveweatheringatthehigher

altitudebyacceleratingthefreeze−thawprocess．Con，sequently，theacceleratedweatheringwillproducea

0
0

20

ー一望卸、∝だ‥
Od．2．13：05】＋慧語㌘
ト「■−③」好7加l説〃， 0d．2，16：11

釘S叩．29．（刃：刃∞
Fig．11．Groundtemperatureprofilesinmoraines．Altitude，directionofgroundsurface，meaSureddateandtimeat
eachsitearedescribedinthelegend．Eachlocationis；
Q）：upper，（卦：middle，③：lowerparts ofTempeteGla−
Cier，④：leftlateralmoraineneartheoutlet of Lugge
Glacier，and G）：1eftlateralmoraine of Thorthormi
Glacier，Yamada et al．

占 9ever，quitelowerthantheotherthreecases，although terminuswassurveyedfor detecting glacier fluctua−
the siteis one of the twolowest measurement sites．

tionin future．

Diurnalvariationofthegroundtemperatureisconsid−
ered to be negligible below50cm depth（Fujiiand

The observed stratigraphyis shownin Fig．12．
Snowlayerswereoccupiedonlyupper46cm，COnSist−

Higuchi，1976）．Then，aSSeeninFig．3（a）andFig．10， ing of2cm new snow on the surface and granular

nolarge changein daily mean temperature during

these3days can be recognized．Moreover，allthe

SnOWOf2to46cmindepth．Belowthisdepth，allthe

parts were constituted of superimposedice．Three
Other measurement sites have similar ground direc− distinctblackdirtlayersweredetectedat46to50，151
tionsfromSSEtoSWasS ofthecase⑤．Although to157and252to256cmindepths and also several

data andinformation arelimited and not enoughto
brownsemi−dirtlayersarefoundinthecores．Accord−
iudge still，this differenceinthe temperature profile 1ngtO thepreliminary algae analysis，thesedirt andmightbeattributedtoexistenceofpermafrostintheSemi−dirtlayersconsistofalgalbiomass．Thesealgae
moraine of ThorthormiGlacier．If the permafrost
are assumed to be bred at surface during summer
actuallyexiststhereanditisgraduallymeltingaway，
SeaSOnandcreatevisibledirtlayers．Therefore，algal
Strengthofthemorainestructurewouldbeweakened
biomass profile could be applied to core dating，
against GLOF，Whichis worriedin future at the
because peaksintheprofile wouldindicate summer
ThorthormiGlacierwhenabigglacierlakewouldbe
Surfaces（Yoshimura et al．，2000）．Theuppermostdirt
formed from the present many supra−glacialponds．

Further investigation on the moraine structure andmonitoring of its change are expected for the risk
assessment offuture GLOFt

8．Observation ofa debris・freeglacier

A debris−freeglacier wasinvestigated on Ganju

LaGlacieronthenorthslantofGaniuLa（Ganjupass，
SeeFig．1）．A50cmdepthpitobservationanda614cm

depthcoredrillingwereperformedatthesamesiteon
the upper part of the glacier to obtain annual net
accumulationandalgalbiomassconcentrationinthe
glacier body．Chemicalsamplings were also carried
Outatboththepitandcores．Microorganismsonthe
glacier surface affecting the surface albedo wereSampled at three altitudes ontheglacier at5000m，4850m and4750m a．s．1．for the purpose to clarify

altitudinalchangeinbiomassandspecies−COmpOSition
Of the microorganisms．Thelocation of the glacier（■）D。n鵡y（〆ml）
O．0

0．2

0．4

layercouldbeassumedtobecreatedinthesummerof
2002，SuggeSting the net accumulationin thelate

Summer Of2002to be22．1cmin water equivalent．

Further analysis ofthe algalbiomassis expectedto
revealtheannualnetaccumulationinthisglacier．
Structuresofalgalcommunityintheicecoresare
being analyzedinlaboratory，because those would
provideusefulinformationtojudgewhetherthedril−
1ingsitewasinaccumulationareaorinablationarea．
AnalysISOfthepolleninthecoresisalsoplannedin
future．Pollen scatteringis concentratedin a short
SeaSOn，andtheseasondependsonthespeciesofthe

po11en．Therefore，analysisofpollenconcentrationsin

thecoreswithidentificationoftheirspeciescouldgive

goodmarkersforcoredating，tOO，aSAmbach et al．
（1966）triedit for pit samples．Further studies withthesemultiplemethodsareexpectedinnearfuturefor

accuratecoredatinganddeterminingthe annualnel二accumulationinthisglacier．

（b）翫m止i卵Phy（G）S咄脚hy

0．8
N●W8nOW●●

Gwul8rOnOW

︵
■
0
︶
l
l
O
凸

卸
側
知

Fig．12．a）Pitdensity，andstratigraphyatthedrillingsiteobservedbyb）pit，andc）stratigraphyoficecores．

リりBulletin ofGlaciologicalResearch

Thefieidworksintheautumnof2002wascarriedoutin the basis of preliminaryinvestigation as the

Plateau：aCaSeStudyofairtemperatureincreaseforthreeglaciers，AnnalsofGlaciology，16，8994
Ageta，Y，，Naito，N．，Nakawo，M．，Fujita，K．，
first year aCtivity of the three−year −joint research
Pokhrel，A，P．andWangda，D．（2001）：Studyprojectonthe
project betweenJapan and Bhutan．Re−SurVeyS andrecent rapid shrinkage ofsummer−aCCumulation type gla−
data collectionsfromtheinstrumentSinstalledin2002
CjersintheHima】ayas，19971999．BulletinofGlacjo】ogjca】
Research，18，4549
areplannedintheautumnof2003．There−SurVeySwi11
Ambach，W，，Bortenschlager，S．and
Eisner，H．（1966）：Pollen−
revealaccurate expansion rate／process of Lugge
analysisinvestigationofa20mfirnpitontheKesselwand−Tsho，andannualmassbalance，Surfaceloweringand
ferner（OtztalAlps）．JournalofGlaciology，6（44）233236．
flow velocity of Lugge，Thorthormiand Ganju La
Chikjta，K．，Jha，］．andYamada，T．（1999）：Hydrodynamjcsofa
Glaciers，and terminalretreat of Ganju La Glacier．
Supra−glaciallake andits effect on the basin expansion：
Tsho Rolpa，RoIwaling Valley，NepalHimalaya．Arctic，Annualconditionsofhydrologyandmeteorologywi11
AntarcticandAlpine Research，31（1）5870．
be also obtained by means of the automatic data
Fujii，Y．and Higuchi，K，（1976）：Ground temperature andits
loggersinstalledin2002．These studies are stillon−re】ation to permafrost occurrencesjn theKhumbu reglOngolng．After harvestlng above mentioned data，and Hidden Valley．Seppyo，38，Specialissue，125−128．
detailed discussionswi11be expected■for the glaciers
Fushimi，H．，Ikegami，K．，Higuchi，K．and Shankar，K．（1985）：
Nepalcase study：CataStrOphic floods．Techniques forand the glacierlakesin Lunana reglOn，Bhutan
predictionofrunofffromglacierizedareas，IAHSPublica−
Himalayas．
tion no．149，125130．
Fushimi，H．andOhata，T．（1980）：Fluctuationsofglaciersfrom
AcknowLedgments
1970to1978in the Khumbu Himal，Nepal．Seppyo，41，Specia＝ssue，7181．
Gardner，J．S．（1992）：Thezonationoffreeze−thawtemperatures
We are high1yindebted to Mr．DorjiWangda，
at a glacier headwall，Dome Glacier，CanadiallRockies．
DirectorofDepartmentofGeologyandMines，Minis−
PeriglacialGeomorphology，John Wiley＆Sons，Chiches−tryofTradeandIndustry，the RoyalGovernment ofter，89102．
Bhutan，forthevaluableassistanceandsuggestionsto
Inoue，］．（1976）：ClimateofKhumbuLiimal．Seppyo，38，SpeciaJ
Japan−BhutanJoint ResearchProject．Wealsothankissue，66∩73．
Karma，Ageta，Y．，Naito，N．，Iwata，S．and Yabuki，H．（2003）：
allthe Bhutaneseconcernedwiththe projectin2002
Glacier distributionin the Himalayas and glacier shrink−
fortheirsupportstothelaboriouslogistics．Wethankagefrom1963to1993intheBhutanHimalayas．Bulletinof
Prof．Yutaka Ageta and Dr．Akiko Sakai，Nagoya
GlaciologicalResearch，20，2940
University，for their helpfuladvices and suggestions
Maidment，D．R．（ed．）（1993）：HandbookofHydrology．McGraw・
onourresearchplans，tOO．
Hill，Inc．，New York，1045pp．
Sakai，A．，Takeuchi，N．，Fujita，K．andNakawo，M，（2000）：Role
TheresearchactivitiesarefundedbyGrant−in−aid
ofsupraglacialpondsin the ablation process of a debris−
forscientificresearch（No．13573004andNo．13373006）
COVer・ed glacier in the NepaJHimalayas．Debris−Coveredfrom the Ministry of Education，Culture，Sports andGlaciers，IAHS Publicationno．264，119130．
Technology（MEXT），theJapaneseGovernment．
Yamada，T．（1998）：Glacierlake andits outburst floodin the
NepalHimalaya．Monographno．1，DataCenterforGlacierResearch，Japanese Society ofSnowandIce，96pp．
References
Yamada，T．，Sakai，A．and Naito，N．（2003）：Ontheformation
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