BulletinofGlaciologicalResearch21（2004）45−48

45⑥JapaneseSocietyofSnowandIce

Recentthickeningtrend ofG［aciar Perito Moreno，SOuthern Patagonia
PedroSKVARCAl，RenjiNARUSE2and Hern畠n DEANGELISllInstitutoAnt孟rticoArgentino，Cerrito1248，ClOlOAAZ BuenosAires，Argentina

2InstituteofLowTemperatureScience，HokkaidoUniversity，SapporoO60−0819Japan（ReceivedSeptember19，2003；RevisedmanuscriptreceivedOctober31，2003）

Abstract

Surface elevations were measured five times at the ablation area of Glaciar Perito Moreno，

SOuthernPatagonia，i．e．inaustralsummers1990，1993，1996，1999and2002．Themeanice−thicknalongatransverselineslightlydecreasedfrom1990to1996，butincreasedbyabout5mfrom1996to2002．Whereas，theice・thicknessalongalongitudinallineincreasedaboutl．5mfrom1990to1993，
remainedalmostunchangedbetween1993and1999，andincreasedsignificantly（morethan6m）from
1999to2002．Theaveragethickeningratesateightpointsalongbothlinesinthemid−reaCheswere＋
0．2ma￣1in1990−93，−0．1ma￣1in1993−96，＋0．5marlin1996−99，and十1．4ma▼1in1999L2002．Thus，

While theglacier was almostin equilibriumin the early half of the1990s，it has been thickening
recentlyatacceleratingrates．Basedonfieldobservationsofsurfacestructuresandoninformation

Ofterminusfluctuations，thiscurrentthickeningtrendisunlikelyrelatedtoasurge．Thoughitmay
beduetodynamiccausesoftheglacierorpositivemass−balance，thedetailedmechanismsarenotyet
Clear．Asaprobableresultofdetectedglacierthickening，anice−damhasformedin2003andthewaterlevelinBrazoRicostartedtorisefromNovember，indicatingthatapossiblerupturemayoccuragain
in the near future．

1．lntroduction

Thickening or thinning rate of a glacier can bederived from the difference in surface elevations

measured in different times at a point fixed to theSpaCe．AtGlaciarSolerinnorthernPatagonia，mean
thinningrateswereobtainedas5．2ma▲1between1983
and1985（Aniya and Naruse，1987）and3．2 ma￣1
between1985and1998（Naruse et alリ2000）．Insouth−

ern Patagonia，a COnSiderablylargethinning rate ofll．1maJIwasmeasuredneartheterminusofGlaciar

2．Glaciar Perito Moreno

GlaciarPeritoMorenoflowsalongadistanceof
about25km as an eastward outlet glacier of Hielo
Patag6nicoSur，thelargeroneofthetwoicefieldsin
SOuthern South America．The drainage area wasestimatedat257km2（AniyaandSkvarca，1992）；theaccumulationandablationareascompriseabout70％

and30％ofthetotalglacier area，reSpeCtively．The

ablationareaisavalley−typeglacierwithabout15kminlengthand4kminwidth（Fig．1）．Theterminusof

Upsalabetween1990and1993（Skvarca et al．，1995） the glacier calvesinto Canaldelos Tempanos andandintheupperpartofGlaciarTyndallablationarea

Brazo Rico（Fig．2），the southwestern arm of Lago

Values measured at other glaciers around the world

theglacierhadbeensteadilyadvancingfromtheend

thickness of Glaciar Perito Moreno has remained

andrupturesoccurredatintervalsofonetofiveyears

4．Oma−1between1985and1990（Kadota et al．，1992）（1ake）Argentinoatanaltitudeofabout180ma．s．1．
and3．1ma．1between1990and1993（Nishida et al．，
AccordingtoRaffoetal．（1953），Liss（1970），Aniya
1995）．These thinning rates are muchlarger thanand Skvarca（1992），and Skvarca and Naruse（1997），（IAHS／UNESCO，1998）．On the other hand，theicealmost unchanged from1990to1996（Skvarca andNaruse，1997）．

Of19thcentury to1917，and theice−dam formations
duringtheperiod1930r1990，beingthe1988break−up

event thelast recorded．Since1990to the present

Thepresentpaperreportsonnewresultsofsur・ （2003），theglacierterminusisalmoststable，tOuChing

face profile of Glaciar Perito Moreno measured in
December1999and2002，andondetailedanalysesof
Changesinice−thicknessfrom1990to2002．

in occasions the opposite bank at peninsula Magal−
1anes with a huge tunnel−Channelthrough which thelakewaterisdrainedfromBrazoRicotoCanaldelosTempanos，aSShowninFig．2．However，thesizeand
diameter of the tunnelor the width of the channel，

46BulletinofGlaciologicalResearch

Fig．1．MapoftheablationareaofGlaciarPeritoMoreno．
The shape of the glacier terminus roughly represents
thatin1990−95．Solidcircleswithnumbersfromltoll
indicate the survey pOints．Ofllpoints measuredin
1990，thepoints5and7wereneveraccessiblehereafter
due to existence of heavy crevasses andlarge ponds．
Mark十indicatesthe controIstation（CS）forthe sur−veys，andBCisthebasecamp．
3．Method

Surveys of surface elevation were made fivetimes at middle reaches of Glaciar Perito Moreno

ablationarea，i．e．inNovember1990，November1993，April1996，December1999andNovember2002．
AcontroIstation（CS）wasestablishedin1990at
about430m a．s．1．on the southern（right−Side）bankabout5km from theglacier terminus（Fig．1）．An

azimuthpointwassetupataboutlOOmapartfrom

Fig．2．Glaciar Perito Moreno terminus viewed from Co．
Morenoon24February2000．Totheleft（north）isCanaldelosT壬mpanosandtotherightBrazoRico．Between

the twolake armSispeninsula Magallanes，Where anice−damisformedwhentheglacieroverridestherock

Oftheoppositebank．Thelackofvegetation（barerock）
along the coast of Brazo Ricois by water erosion，

indicatingthemaximumlakelevelreachedinthepast
dueto formation of anice−dam．

Whicheverisformed，Changeseasonally．

CS．For the surveys，an electronic distance meter（TopconEDM−TheodoliteGuppy），Oralaserdistancemeter（GeoFennel，Model：Pulsar50）andatheodolite（ZeissTh−2）oradigitaldistance−anglemeter（PentaxPTS−V3）wereutilizedatthecontroIstation；areflec−

tor was placed by a mobile team at survey points
around350r360ma．s．1．ontheglacier．

Threedimensionalcoordinatesofllpointsalong
ahalf−tranSVerSelineandthelongitudinalcenterline（Fig．1）were determined by the first measurement
Carried outin November1990．In the second，third，fourth and fifth measurements（1993，1996，1999and2002），thesamesurveypointsasin1990werelocatedIncontrasttomajorcalvingglaciersinPatagonia
Which have been retreating considerably at a range
fromlkmto13kmduringthelast50years（Aniyaet

Withanaccuracyofonefoot（about30cm）byusing

Perito Moreno seems to have been in a rather stable

notaccessibleduetotheexistenceofheavycrevasses

the raw data ofthe horizontalangles and distances

measuredin1990．Ofllpoints，afewlocalitieswereal．，1992；Aniya，1999；Naruse et al．，1995a），Glaciar

State（Warren，1994；SkvarcaandNaruse，1997；Rott Orlargesupraglacialponds．
etal．，1998；Stuefer，1999）．

47

Skvarca et al．

4．Results

3

Meanannualice・thicknesschangesdeducedfrom

thedifferenceofsurfaceelevationsareshowninFig．

3，Separatelyforthefourperiods1990−1993，1993−1996，1996−1999，and1999−2002．Since the1996ASurVeyWaS

madeinApril，themeasuredelevationwasrectifiedto﹁二三て■E︼

UO
もtheprobablevalueinNovember，aSSumingtheemer− ＞
心gencevelocity（12marl）andthesummerablation（9m二Ofice），basedonNaruse et al．（1997）．Sincethereare ︼U
numerouscrevasses，depressions，andicemoundsup

to severalmeters highon the glacier surface，themeasuredsurfaceelevationchangesarepartlycausedby the development or decay of the surface undula‑tions．Judgingfromthesurfaceconditionsaroundthe
SurVey pOints，We rOugh1y estimate this effect assmaller than±0．5ma￣l．

ハリ

5 8

3 5 6

3 5 ▲

U
再㌻
コS
1990

1993

1996

Year

1999

2002

transverseandlongitudina11inesinthemiddle−reaChes
oftheablationareaofGlaciarPeritoMorenofrom1990
to2002．

2

aboutl．5mfrom1990to1993，thenalmostremained

unchanged until1999，and thickened more than6mfrom1999to2002．
The averagethickeningrates ofeightpoints on

10李葛卜

36Fig，4．Changesin the mean surface elevations along the3二．
︒
∈一
ヱ
≠
−ぎ

36 つL＋

thebothlinesinthemid−reaCheswerecalculatedas＋
0．2ma−1in1990−93，−0．1ma1in1993−96，＋0．5ma−1in1996−99（assumingtheconstantthickeningratesin
1993−99atthepoints2，3and4），and十1．4ma￣1in1999−2002．Thus，While the glacier exhibited almost a10123【8rizont81di5t8nCe【km】
Fig．3．Distribution ofthe annualthickness change rates
during the periods November1990 November1993（Naruse et al．，1995b），November1993 Apri11996（SkvarcaandNaruSe，1997），Apri11996Decemtx！r1999，
and December1999−November2002（present study）．
Thepositivesignindicatesthickeningandthenegative
Signthinning．Numbers（1，2，．．．andll）attachedtosolid

Circlesindicatesurveypointnumbersfromltoll（seeFig．1）．

Figure3exhibitsthat thickeningratesfluctuate

Steadystateprofileintheearlyhalfofthe1990s，itis
recentlythickeningwithanacceleratingrate，thatis

Slgnificantlylargerthanthemeasurementerrors．Thi＄

thickening trend was also qualitatively confirmed
through field observations which indicated that theSOuthernlateralmarglnWaSapprOXimatelylOto20m
higherinDecember1996and1999thaninNovember

1990and1993．Inaddition，prObablyduetotheobser−
Vedglacierthickeninganice・damhasformedagainin

2003，impedingthewaterdrainagefromBrazoRicoto

Canaldelos Tさmpanos．As a result，the waterlevel

Started to risein Brazo Rico from November2003，

between＋1．5ma▼1and−1marlfrompointtopoint，
predictingapossiblefuturecollapseoftheiceTdam，anexcept atthepointsl，2and3in19992002．Data at event not observed since1988．
thepointll，thenearesttothelateralmargin，eXhibitsadifferenttrendtootherpoints，thatmaybedueto5．Discussion and conclusions

longitudinalprofile．
Thetemporalchangesinmeansurfaceelevations

bycomparingthedigitalterrainmodelsbetween1975
and1995，Whichrepresentsameanthickeningrateof

Thoughthetransverselineslightlythinnedfrom1990
to1996，ithasthickenedbyabout5mfrom1996todatawiththeloopedpatternofmedialmoraines，they

thedifferentflowpatternandsurfacemelting．There−
fore，Omittingthepolntll，Wetakeaveragesofthick−
AtGlaciarP‡0ⅩⅠ，aVeryhighflowspeedofupto
nesschangeoverfourpointslO，9，8and6alongaline
50mapIwasmeasurednearthecalvingterminusinthat we callthe transverse profile，and over four1995（Rivera et al．，1997），andtheaveragethickening
pointsl，2，3and4along aline that we callthe Oficeof44mwasrecognizedovertheablationarea

alongthesetwolinessince1990areshowninFig．4． 2．2ma−1（Rivera andCasassa，1999）．Basedonthese

2002．Whereas，thelongitudinalline thickened by

SuggeStedapossibilityofsurgingin1976and1992−94．

In many surging glaciers，thickeningis often

BulletinofGlaciologicalResearch

4βobserved first in the upper reaches and the bulges
propagatedown−glacierasasurgefrontwithaspeed
Ofafewtimesthenormaliceflowspeeds．Beforethe

Trapridge Glacier，Yukon Territory，Canada，1969−89，）．
Glaciol．，37（125）158169．
IAHS／UNESCO．（1998）：Fluctuations of Glaciers1990−1995，Vol．VH，Zurich：WorldGlacierMonitoringService．
Surgein1982−83at Variegated Glacier（Alaska），theKadota，T．，Naruse，RリSkvarca，P．and Aniya，M，（1992）：Ice
ice thickened more than 50 m during 8 years
flow and surfacelowering of TyndallGlacier，SOuthern
Patagonia．Bull．GlacierRes．，10，6368．
（Raymond and Harrison，1988），and at Trapridge
Glacier（Canada）awave−1ikebulgepropagatedwitha Liss，V．C．C．（1970）：DerMorenogletscherinderPatagonischen
Kordillere：Seinungewohnlichesverhaltenseit1899undder
Speedofabout30ma1between1980and1989（Clarke
eisdammdurchbruchdesjahres1966．ZeitschriftfurGlets−and Blake，1991）．
CherkundeundGlazialgeologie，Vl（1−2）161180．
Because at Glaciar Perito Moreno the measurer
NaruSe，RリAniya，M．，Skvarca，P．and Casassa，G．（1995a）：
Recentvariationsofcalvingglaciersin Patagonia，Southmentsweremadeonlyatafewprofileslocatedinthe
America，reVealed by ground surveys，Satellite．data ana，ablationarea，Wehavenoinformationonwhetherthis
1yses and numericalexperiments．Ann．Glaciol．，21，297

thickeningtrendis a phenomenonoccurringallover
theglacieroronlyalocalone，1ikeabulgetraveling

downtheglacier．However，therearenoevidencesof

Surge−1ike behaviors or any signs of surge on theglaciersurface and atthemargins ofGlaciar Perito
Morenoduringthelast20to30years．
Thus，We COnClude that this current thickening
trendis notlikely related to a surge，but may be
attributedtodynamiccausesorpositivemass−balance

Oftheglacier．The detailed mechanisms areleft un−clear untilmore elaborate studies are madein thefuture．
Acknowledgments
We would like to express our deep thanks toCompa員ia Hielo y Aventura and their mountainguidesforthelogistic support and assistance during
the field campaigns．Thanks are also due to manypark rangers of Parque NacionalLos Glaciares，

Administraci6ndeParquesNacionales，fortheirvalu−−303．

Naruse，R．，Skvarca，P．，Satow，K．，Takeuchi，Y．andNishi
K．（1995b）：Thicknesschangeandshort−termflowvariation
OfMorenoGlacier，Patagonia．Bull．GlacierResリ13，2128．
Naruse．R．，Skvarca，P．andTakeuchi，Y．（1997）：Thinningand
retreating of Glaciar Upsala，and an estimate of annual
ablationchangesinsouthernPatagonia．Ann．Glaciolリ24，485−491．

Naruse，R．，Yamaguchi，S．，Aniya，M．，Matsumoto，T．
Ohno，H．（2000）：RecentthinningofSolerGlacier，nOrthern
Patagonia，South America．Data ofGlaciologicalStudies，Institute of Geography，Russian Academy of Science，
Moscow，Publication89，150r155．
Nishida，K．，Satow，K．，Aniya，MリCasassa，G．andKadota，T（1995）：Thickness change and flow of TyndallGlacier，Patagonia．Bull．GlacierRes．，13，2934．
Raffo，）．M．，Colqui，B．S．and Madejski，M．E，（1953）：Glaciar
Moreno．RevistaMeteoros，AnoIII，No．4，Oct．−Dec．，（Direc−
ci6n GeneraldelServicio Meteoro16gico Nacional，Pub，
1icaci6n No．9，Buenos Aires，Repdblica Argentina），293
341．

Raymond，C．F．and Harrison，W．D．（1988）：Evolution ofVarie−gatedGlacier，Alaska，U．S．A，，priortoitssurge．］．Glaciol．，34（117）154−169．

Rivera，A．and Casassa，G．（1999）：Volume changes on P吉0ⅩI
ablecontributionduringfieldmeasurements．Weare
glacier，Patagonia：19751995．Globaland Planetary
gratefulto areviewerforthecomments．
Change，22，233−244．
Rivera，A．，Lange，H．，Aravena，J，C．andCasassa，G．（1997）：Th
20th−CenturyadvanceofGlaciarPfoXI，ChileanPatagonia．
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