9J

Bul1etinofGlaciologicalResearch21（2004）91−96⑥JapaneseSocietyofSnowandIce

WatersurfacewavesinducedbycalvingeventsatPeritoMorenoGlacier，SOuthern Patagonia
Yasuko HZUKAl，Shun，ichiKOBAYASHl2and RenjiNARUSE3

1TheGraduateUniversityforAdvancedStudies（SOUKEN），NationalInstituteofPolarResearch，Tokyo1738515Japan
2ResearchInstituteforHazardsinSnowyAreas，NiigataUniversity，Niigata950−2181Japan
3InstituteofLowTemperatureScience，HokkaidoUniversity，SapporoO600819Japan（ReceivedOctober6，2003；RevisedmanuscriptreceivedNovember21，2003）

Abstract

Inordertoinvestigatecharacteristicsofwatersurfacewaves，inducedbycalvingeventsofPerito
Moreno Glacier，a Water preSSuregauge WaSSet at the shore of proglacialLake Brazo Rico for aperiodfrom2to13December1999．Continuousmeasurements oflakelevelshowthatthe diurnal
numberofcalvingeventsisnotrelatedtotemporalvariationsofairtemperature，butthatthehourly
eventnumberonthedayweaklydependsonthetemperaturerise．Thespectralanalysisforlakelevel

revealed that surface waves are strong mostly at ca．0．02Hz and secondly at ca．0．04Hz．Thesefrequenciesprobablycorrespondtoinherentfrequenciesofsurfaceseicheintheproglaciallake．

1．lntroduction

2．Observation

IntheSouthernPatagoniaIcefield，itisseenthat，
The observation of calving events at Perito
inrecentdecades，mOStglaciershaveretreated，buta MorenoGlacierinsouthernPatagoniawascarriedout

fewofthemhavestagnatedorevenadvanced（Aniyaand Skvarca，1992；Naruse et al1995）．Therate of

inproglacialLakeBrazoRicoforaperiodfrom2to
13December1999．A schematic map of thelower

terminusadvanceofcalvingglaciersisoftenexpres−SedasadifferencebetweentheglacierflowrateandreachesoftheglacierisshowninFig．1．Theglaciernusresponsedoesnotdirectly relate to the regional
Climate trend，but can be controlled by the calving
dynamics and topography．Hence，detailedSkvarcaetal．（2004）reportedthattheglaciertendsto

thecalvingrate．Warren（1994）statedthatthetermi−

isatemperatefreshwatercalvingglacier，locatedon
theeasternsideoftheSouthernPatagonianIcefield．
thickenwiththestableterminusintherecentyears．

Studiesoncalvingrateareimportanttounder−Standtherecentretreatofcalvingglaciers．An
interestingissuein the study of calvinglS a
differenceinthecalvingmechanisms offresh−
Water and tidewater glaciers．According toBrown et al．（1983）thecalvingrateis propor−

tionaltomeanwaterdepthalongtheterminus
forthreetidewatercalvingglaciersinAlaska，Whichhaverapidlybeenretreating．
ThisreportpresentsaresultofareconnaisLsance study to investigate calving phenomena
quantitativelyandqualitatively，uSinga waterpressure gauge in a proglaciallake．This
methodenablesustoobservecalvingactivities
duringbothdaytimeandnighttime．Continuous
observations and spectral analyses for water
Surfacewaveswillprovidestatisticalinforma−tion for calving phenomena，e．g．hourly anddailyvariationsincalvingevents andspectralfeaturesofwaterwavesinducedbytheevents．

Fig．1．MapoftheterminalpartofPeritoMorenoGlacier．
WLG indicatesagaugingsiteofwaterlevelinprog−
1acialLakeBrazoRico． BC indicatesbasecampsite．

Bulletin ofGlaciologicalResearch

92

marked pinnacles，Glto G5and G7，On thelateral
marginoftheglacierterminus（Fig，2；alsoseeFig．1）
datalogger，WaSSet at aboutO．6mbelowthewater
Awaterpressuregauge，COnneCtedtoacompact

surface at site WLG near the shore of Lake Brazo

Rico，intowhichPeritoMorenoGlaciercalves（Fig．1）．

Theeffectofdynamicpressureisconsideredasneg−
iigiblysmallbecausethesensorofthepressuregauge
wascoveredwithanumberofstonesofvarioussizes
atthebottomofthelake．Figure2showsasketchof

thedistancefromthegauglngSitetothecalvingcliff
isabout400m1500m，andtheheightoftheicecliff
ranges from about40 m to 70m above thelake

Surface（Naruse et al．，2001）．The accuracy of theWaterpreSSuregaugeis±20mmwiththeresolution
Oflmm．Therecordingintervalwas5sfortheearly
theglacierterminus，thelakeshoreandsiteWLG（see 9days and15s for the residua13days because ofbattery shortage．The data atlonger timeintervals
Fig．3）．According to an opticaltopographic survey
fromtwocontrolpoints，αandβontheshoretosix WerenOtuSedforthespectralanalysis．

Fig．2．Schematic picture of measurlng pOints and theCalvlnglCeCliffneartheglacierterminus．Solidcircles
Ontheglacierindicatemarkedpinnaclesmeasuredfrom
thebaseline（αandβ）．Thewaterlevelgaugewasset
near the shore of thelake Brazo Rico． MS indicates
MeteorologicalStation，Wheretheglobalradiationand
Airtemperatureweremeasured．

Fig．3．Photographofthemeasurementsite．Awaterlevel
gaugewassetupbesidetheexposedsmallrockinthelake near theshore．The calvingice cliff can be seen
behind thelake．

Iizuka et al．

鼠ヲ

3．Resu圧S

4．AnalysISandconsideration

The12−dayobservationsupplieddataof16hours
in total，and consequently68series oflarge calving

J．ノ．几坤・ 川〔′／J川〃・小ノ川川わ（、JT（リ■（、汀ノ油

WaVeS Were detected．The68seriesinclude15series

recordedat15sintervals．Eachseriesoflargecalving

WaVeS WaS COmpiled for the number，date，time，

maximum amplitude anddurationtime．Anexample
ofthiswaterleveldataon2and3Decemberisshown

To examine factors affecting calving activity
uslngthedataofthe68seriesoflakelevelforlarge
Calving events，the daily number of the eventsis

ShowninFig．6．Theeventnumberswerelargefor6

to9December．Themaximum amplitudeswere also

largeon7and8December．Similarly，thenumber ofinFig．4．Generally，eaChseriesofcalvingwaveshows Calving events occurrlng eaCh hour on alldaysis

the maximum amplitude at the beginning and lasts
SeVeraltensofminuteswiththeamplitudedecreasing
towards the end．Some of the wave series exhibit

Shownin Fig．7．During daytime hours ofllOO h toCOmplexpatterns，Whenthenextcalvingeventoccur−rs before complete damplng Of the previous waves．
Figure5showsanexampleofwavesforaverylarge
Calvingwhichoccurredatl152hon3December．The

around1800h，the number of events was relatively
highandthemaximumamplitudewasalsolarge．
Global radiation and air temperature variations
measured near the gauging site at Perito Moreno

Glacier（markedas MS inFig．2）areshowninFig．8．

MonthlyaveragetemperatureinDecember1999wasmaximumamplitudeofthewaveswasO．48m，andthis 9．90C and the maximum andminimum temperatures

series continued for about50minutes．

Were19．6and2．80C，reSpeCtively．Thevariationofair

1．1t l1．2∈し ■■■■上りtむ
Aむ︻・Hむー電渉ハVOu八U

八U

1：UUr）（・C．2

9：00

曇4：00 19：00

0：00l）（汀t．3

5：0010：（IO 15：00

Fig．4．Variationsinwaterlevelon2and3December1999．
The horizontalaxisshowsthelocaltime．

CaしvjnglJ8Ve

一む＞
聖﹂
・ここ完
MOO一人︶

一q

0．2

11hOml〜hOロm

1Zh20m12hん8mDecember 3rd

Fig．5．Anenlargedrecord ofwavescausedby a calving
event on3December．

20：（川BulletinofGlaciologlCalResearch

.94

∵∪
．
さ﹁−二一∈︵1U﹁一uX
和≡0402しぶ∈⊃Z
老害
山OU

2 3 4 5 6 7 8 9 ‖）111213
December 1999

Fig．6．Dailynumberofcalvingevents（bars）andthemaximumamplitudes
ofcalvingwaves（opencircles）fortheobservationperiod・門
∈﹈
む
0p
コ二；
ハEV U
≡∈ O
叫 0莞
笈

6554433hむq∈nZ
壱む
A﹈

21

ハU
0246810 12 14 161EE 20 22 24l．1つt、illTimし、

Fig．7．Hourlynumberofcalvingevents（bars）andthemaximumamplitude
ofthecalvingwaves（opencircles）onthedayforallthedata・﹇ ハ0 0㌣ リ
0 0E連0山ロ 0uリO
こ汚
毒 64 0ぷ
一票 200蒜

250251000

2 3 4 5 6 7 8 9 1011

甲山
巴n登監
E心一遍・
lDecember．1999

Fig．8．Variationsinglobalradiation（thinline）andairtemperature（thickline）atPeritoMorenoGlacier（measuredbyHelmutRott）・

Iizuka et al．

9ごitemperatureinFig．8doesnotappeartoberelatedto

Fig．10．The first dominant peak exists mostly atresults suggest that theice−melt by air temperaturerisehelpstofractureiceorenhancesglacierflowto

Seicheis a free surface oscillation which occursin

thedailynumberofcalvingeventsinFig．6．However， around O．018Hz and secondly at around O．037Hz，
thehourlycalvingnumberinFig．7isrelatedtothe
althoughthepowervalueshave awiderange．Thesetemperaturerise duringthe day；Calvingeventsmay
peaksprobablycorrespondtotheinherentfrequencies
OCCurin response to daily temperature rise．These
Ofsurfaceseicheintheproglaciallake．Thesurface
inducecalving．

J．二∴．ヤい・／＝′■−川．／／ト、J、Using the Fourier Transform，pOWer SpeCtra Of
Calvingwaveswerecalculatedforeachcalvingevent．
Fortheanalysis，pOWerSpeCtraWereCalculatedat arangeofO．001toO．1Hz．Anexampleoftheanalyticalresultsis shownin Fig．9．There are three definite

responsetothelake−basinscale（HorneandGoldman，1994）．Ifthelakedepthandhorizontaldistancewere
given，theinherent frequency could be calculated．

However the data are not accurate enough at thisStage．Furtherinvestigations of thelake topography
are needed．

5．Concludingremarks

powerpeaksatfrequenciesofO．018Hz，0．023Hzand WaterlevelvariationsinproglacialLake Brazo
O．036Hz．Thespectralpowerofthreedominantpeaks
Rico of Perito Moreno Glacier show that surface

fora11thetimeseriesareplottedwiththefrequencyin

WaVeS，inducedby calving events，COmmOnly have a

PoNer SPeCt「Urn Of caしving tJaVenV﹇S一b︵U■ヽ一︻U てO ﹂﹂
n ﹁むコU ∠ONE﹈

ヰd0．DO

O．02

0，0ん

0．0る

F「equency［Hzコ

0．08

0．10

Fig．9．AnexampleofpowerspectracalculatedforacalvlngeVent．

﹇SN∈﹈﹂￠きO
d0．00

0．020．04
Frequency［Hz］

0．06

0．08

Fig．10．Distributionsofthethreedominantspectralpeaksonfrequencies．

9fi

Bulletin ofGlaciologicalResearchwave shape with aninitialpeak．Thereis no clear
relationship between the air temperature and daily
number ofcalvingevents，but the hourly number of
eventsinthedayislikelytoberelatedtohourlyair

References

Aniya，M．andSkvarca，P．（1992）：Char・aCteristicsandvariations
OfUpsalaandMorenoglaciers，SOuthernPatagonia．Bulle−
tinofGlaciologicalResearch，10，3953．
temperaturerise．Asaresultofspectralanalyses，theBrown，C．S．，Meier，M．F．andPost，A．（1983）：Calvingspeedof
waveamplitudepeakedaroundO．02Hz．Itispossible
Alaska tidewaterglaciers，With application to Columbiathat this frequency corresponds to theinherent fre−glacier．U，S．GeologicalSurveyProfessionalPaper，1258−C，Cl−C13．
quencyofsurfaceseicheintheproglaciallake．
Horne，A．J．andGoldman，C．R、（1994）：Limnology．McGraw−
Hill，Inc．，Tokyo，576pp．
Acknowledgments
Naruse，R．，Aniya，M．，Skvarca，P，and Casassa，G．（1995）：
Recent variation of calving glaciersin Patagonia，SouthWe express our sincere thanks toIng．Pedro
America，reVealed by ground surveys，Sate11ite−data ana．
1ysesandnumericalexperiments．AnnalsofGlaciology，21，
SkvarcaofInstituteAnt孟rticoArgentinowhohelped

us duringthe field observation．We also appreciate
Dr．Helmut Rott ofInnsbruck Universitywho kindly
Offeredthepreciousmeteorologicaldatameasuredat

Perito Moreno Glacier．We also acknowledge Dr．

Kazuhisa Chikita of Hokkaido University for his
criticalreadingofthe manuscript andusefulsugges−
tionsforitsimprovement．Thisstudywassupported

byagrant−in−aidforInternationalScientificResearchProgram（No．10041105）Ministry of Education，Sci−
ence，SportsandCulture，Japan．

297−303．

Naruse，R．，Skvarca，P，andKobayashi，S．（2001）：Measurements
Ofsurfaceheightandflowvelocityatthecalvingterminus
OfPeritoMorenoGlacier，SOuthernPatagonia，inDecember
1999．Glaciologicaland GeomorphologicalStudiesin
Patagonia1998and1999，editedbyAniya，M．andNaruse，Rリ141144．
Skvarca，P．，Naruse，R．andAngelis，H，（2004）：Recentthicken−
ing trend of Glaciar Perito Moreno，SOuthern Patagonia．
Bull．Glac．Res，，Zl，45−48．
Warren，C．R．（1994）：Freshwatercalvingandanomalousglacier
OSCillations：reCent behaviour of Moreno and Ameghino
Glaciers，Patagonia．The Holocene4，4，422429．