37

Bu11etinofGlaciologicalResearch21（2004）37−43
電）JapaneseSociety ofSnowandIce

Morphostratigraphyofmorainesin theLagoTranqui10area，Chi［ean Patagonia

Stephan HARRJSONl，NeilGLASSER2and Masamu ANIYA3

10xfordUniversityCentrefortheEnvironment，MansfieldRoad，0Ⅹford，UK

2CentreforGlaciology，InstituteofGeographyandEarthSciences，University ofWales，Aberystwyth，Aberystwyth，UK
3InstituteofGeoscience，UniversityofTsukuba，Tsukuba，Ibaraki305−8571Japan（ReceivedSeptember14，2003；Revisedmanuscriptreceived November13，2003）

Abstract

ThevalleysdrainingtheHieloPatag6nicoNorteinsouthernChilecontainanumberofmoraine

belts，Whichrecordthepastexpansionoftheicefieldanditsoutletglaciers．Thispaperdescribesthenature ofthemorainesintheExploradoresvalleywhichdrainsthenorthernflanksoftheicefield．
Fourmorainesequencesaredescribedanddifferentiatedonthebasisoftheirmorphostratigraphic
relationships．Themorainesreflectstagesofrestrictedglaciationconfinedtohighvalleysandmore

extensivevalley−basedglaciation．Theworkprovidesaschemeforasubsequentdatingprogramme．

1．lntroduction

The Hielo Patag6nico Norte lies astride thesouthern Andes between46030

S and47O30′S with an

areaofc．4200km2（Fig．1）．Theoutletglaciersdrain−ingtheicefieldextendtolowerlatitudesthanthoseof
any other substantialice massin the world．The

icefieldisnourishedbythemid−1atitudeweathersys−

tems andischaracterisedby abundantprecipitation，

intheLagoTranquiloareaoftheExploradoresvalley
Which formerly drained the northern flanks of theHielo Patag6nico Norte．The paper aims to placetheseinachronologicalschemebased ontheir mor．
phostratigraphy and provides a classification for a
Subsequentdatingprogramme．
2．Studyarea

highablationrates，SteepmaSS−balancegradientsand
TheLagoTranquiloarealiesattheeasternend
highice velocities．Togetherwith sharplocaltopo− OftheRioNorteandRioExploradoresriversystems，
graphic and climatologicalcontrasts，these circum−
WhichtogetherdrainthenorthernflanksoftheHielo

StanCeSCreate a dynamic andtemperateglaciersys−
tem．

Although there are few detailed mass−balanceStudies，the available evidence suggests that theseglaciers are extremely sensitive to climatic change．
Well，developedmorainesoccurthroughoutthevalleys
drainingtheHieloPatag6nicoNorteandreflectfluc−tuationsoftheoutletglaciers（Harrison，2003）．While

there has been considerable work dating the mostPatag6nicoNorte．Thepresentwatershedlieslkmto

thewestofLagoTranquilo．Mountainstothenorth，SOuth and west nurtured valley and cirque glaciers

during the Quaternary and these，at Various times，COalescedtoproducelargevalleyglaciersinthe Rio
NorteandtheRioTranquilovalleys（Fig．2）．
3．Methods

recent（LittleIceAge）glacialmorainesinthearea（egThe geomorphic and morphostratigraphic relaN
Aniya，1995；1996；AniyaandNaruse，1999；Aniyaand tionshipsoftheLagoTranquiloareawereestablished
Shibata，2001；Glasser et al．，2002；Winchester and through detailed geomorphological mapping of an
Harrison，1996；Winchester et al．，2001；Harrisonand area of approximately35km2．This reglOn eXtends
Winchester，1998；2000）therehasbeenlittle analysis
fromLosCipresesinthewesttoPuertoRioTranquilo

Ofthenatureorageoftheearliermoraines．Althoughthesemorainesclearlyrelateto anearlierexpansion
in the volume of theicefield，Which resultedin theextension ofits outlet glaciers，there has been noprevious attempt at mapping these nor in assessing
theirmorphostratigraphiccharacteristics．
This paper reports on a research project that
aimstoanalysethemorphostratigraphyofmoraines

intheeastandLosTresArroyosinthenorthtothe

Valleysdraininginto Rio Norteinthe south（Fig．2）．

Field mapping was carried out using base maps re−produced from thel：50000ChileanInstituto Geo−
grafico Militarmap4630−7240．

Thegeomorphology ofthe Lago Tranquilo area

iscomplex．Therefore，itiscriticallyimportant thatthe geomorphologicalmaps not only accurately

.38

Bu11etinofGlaciologicalResearch

Fig．1．TheHieloPatag6nico NorteshowingthemainoutJetglaciers．

Harrison et al．

39．
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p
巴
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虐﹄

40

BulletinofGlaciologicalResearchreflect the spatial and genetic complexity of land‑forms，but also summarise the geomorphologyin a
Sufficiently simplified form to enable the viewer toreadily comprehend them（Anderson et al．，1998）．

Consequently，genetically similarlandforms were
mappedco11ectivelyaslandformassemblages，though
SOmeindividuallandforms were represented as dis−tinctentitiestoavoidoversimplificationandtofulfil
the research aims．

4．Glacigeniclandformsandsediments
Gユacia‖andformsintheLagoTranquiloareacan

begroupedintofourdistinctlandformassemblageson
the basis of their morphological and topographic

characteristics（Tablel）．Thesearereferredtoasthe
Stage One，Two，Three and Fourlandform assem−

blages．

J．J‥ヾ／′／ヾ− ‖紬．ヾ山一、∴J／んJJ・在り川．＼、′／高／川／・′ヾヾ．川／一山叶ん助が椚那Stage One moraines are associated with recent
glacierrecessionandarefoundatthesnoutsofcon−

temporary valley and cirque glaciers（Fig．3）．The

Fig．3．Stagelmorainein the vicinity of a smallva11ey
glacier，WeStOfLagoTranquillo．

largestofthesemorainesoccursasaterminalridgein
frontofGlaciarExploradores．

formedduringseveralepisodes ofglacier expansion

ふ、（れJ…J／ざresolvedbyaplanneddatingprogramme．However，inandretreat．Asaresult，thereissomeambiguityasto

the age of the Exploradores moraine，Which willbe

InApri12003，alargelow−1yingwaterloggedarea this paper we tentatively suggest that this moraine
WaSlastincontactwiththeglacierduringtheLittle
Exploradores，preVentingaccesstotheglaciersnout． IceAge．

existedbetweenLagoBayoandthesnoutofGlaciar

Thereforenosedimentarydescriptionswerepossible／．ニ．ヾ／叫t γ1′・り小h・石／ん〃Jイ／∴川ノ＼■−／山肌〃／小ヾり，両神、

at the moraine．

⊥〟〃郎刑椚

Glacier recession from this moraine has been

dated by dendrochronology to the end of the nine−

teenthcentury（Larapers．comm．）．Morainesofsimi−

lar morphology and relationship to contemporary
glaciersarewidelyreportedfromotherglaciersoftheHielo PatagBnico Norte and dated by lichenometry

StageTwomorainesarerestrictedto＜20mhigh
Sharp−CreSted terminalmoraines deposited at themouthsoftributaryvalleysat altitudesabove c．850

metres above sealevel．

and dendrochronology to the LittleIce Age （e．g．
Winchester and Harrison，1996；Winchester et al．，2001）．However，AniyaandNaruse（1999）datedsimi−

1armoraineformationto1300BPintheSolerva11ey
and it is cIear that such moraines may have been

ふ−（〟川ぐ〃′∫Naturalexposuresin the Stage Two moraines
Showthattheyarecomposedentirely ofsandyboul−

der gravel．Althoughtexturally variable，the sandybouldergravelistypicallyamassivebouldergravelin

Tablel・Morphologicalandtopographiccharacteristicsofglaciallandformassemblagesassociatedwith
glacialStagesOnetoFourintheExploradoresvalley．

Altitude range
ofdrift
Maximum moraine
ridgethickness
Moraine ridge
Slopegradients
Maximumdrift
sheetthickness
Bedrockstriations

StageOne

StageTwo

StageThree

StageFour470−700m

180−700m

400−900m

く200−700m

15m

40m

25m

15m

10−25810−30010−40010−25020m

14m

Frequent

Frequent

2▼3m

20m

Notobserved Rare／degraded

4J

Harrison et al．

asandmatrix．Thefollowingproportionsaretypical： that these moraines are composed of two distinct
grave160％，Sand30％andmud＜10％．Clastdistribu− Sedimentary facies，With c．5m of sandy boulder
tionwithin this faciesis variable，with gravel−Sized
graveloverlyingc．10mofsandygravel．

Clasts occurringeitherinclusters orin contact with

One anOther．Lithologicalcounts（n＝100）show thatthe gravel−Sized clasts comprise granite（72％）andSChist（28％）．Thegravel−Sizedclastsarepredominant−1ysubrounded（60％）andsubangular（36％），Withlower
percentages of rounded（2％）and wellrounded（2％）
Clasts．Thelargestbouldershaveb−aXeS Ofuptol．5m．

ん血−ゆナで／α〟りJJ

Thesandybouldergravel，althoughagaintextur−allyvariable，istypicallyamassivebouldergravelin

asandmatrix．Thefollowingproportionsaretypical：
grave160％，Sand30％andmud＜10％．Clastdistribu−
tion within this faciesis variable，With clasts occur−

ringeitherinclustersorincontactwithoneanother．

Lithologicalcounts（n＝100）show that the gravel−
Sizedclastscomprisegranite（60％）andschist（40％）．
The gravel−Sized clasts are subrounded（52％）andSubangular（48％）．Thelargestbouldershaveb−aXeSOf

Texturally，thesandybouldergravelisverysimi− upto2m．

1artothesandybouldergraveldescribedbyGlasser

The sandy gravelfaciesis a moderately wellandHambrey（2002）atthecontemporarymarginsof SOrtedunit，COnSistingofgravel（70％）andsand（30％）．
Glaciar Soler on the eastern side of the Hielo

Patag6nico Norte．Here they wereinter−

Lithologicalcounts（n＝100）show that the gravel−

preted as anice−marglnaldeposit formed
fromthemixingbyglaciotectonic proces−

SeS，Slumpingandstreamsortingofdiffer−ent parent populations（basalglacial，Su−

praglacialand glaciofluvialsediments）attheglaciermargin．Evidenceforthisinter・

pretation comes from the heterogeneous
Sedimenttexture，Clastroundnessandlow

proportions／absence ofstriated andfacet−
ed clasts．

It is clear that these moraines andsediments are older than the LittleIce
Age moraines developed in the region．

However，their smallsize and position

SuggeSt that they reflect a short−1ived cli−mate deterioration，prObably during thelatterpartoftheHolocene．
J．、●∴、ヾ／・伸・7丁伸t く∧Jt・んJ／山〃イバげ川 ヾ−・−／ト

Fig．4．Stage3morainestothewestofLagoTranquillo．

Stage4surfaceintheforeground．

仙リJJ（び∫ぐ〃J抽榔、ん抑所用情StageThreeglacialdepositsandland−

forms formlarge（c．100m high）sharp−

crested terminalandlateralmoraines andaremainlyfoundtothewestandsouthof

LagoTranquillo（Figs．4and5）．Severalof

thelateralmoraines form multiple fea−tures．Boulders are common on their sur−facesand up to8m or soinheight；manyareweatheredwithconsiderablespallingof

Surfacelayers．The altitude oftheseland−
forms falls from600L900metresabovesea

levelinthe east ofthe area to400metresabovesealevelfurtherwest．
ふ−r〃川ぐ〃かAc．15mhighnaturalexposureinthe
inner flank of one of the Stage Threemorainesin the tributary valleys shows

Fig．5．Stage3moraineandStage4drift−COVeredsurface
tothesouthofLagoTranquillo．

BulletinofGlaciologicalResearch

42

Sizedclastscomprisegranite（70％）andschist（30％）．
Thegravel−Sizedclastsaresubrounded（58％），Suban−gular（40％）and angular（2％）．Thelargest gravel−
sizedclastshaveb−aXeSOfuptoO．1m．
J〃／り♪八一血JわJJ

diamictonis a massive，Clast−rich silty diamicton，COmprisinggravel（50％），Sand（40％）andmud（10％）．

The gravel−Sized clasts are typically subrounded（66％）andsubangular（32％），withminorangular（2％）．
Lithologicalcounts（n＝200）show that the graveト
sizedclasts aretypically dominatedby schist（88％）

The sandy boulder gravel in the Stage Threemorainesisinterpreted as aniceTmarginaldeposit
formedfromthemixingbyglaciotectonicprocesses，Slumpingandstreamsortingofdifferentparentpopu−

Withlowerproportionsofgraniteandotherundiffer−

gravelfaciesisinterpreted as a reworked glacioT

themouthoftheRioNorteValley，isprlmarilycom−

entiatedrocks（12％combined）．Striatedandfaceted
Clastsarecommon，withupto26％striatedclastsand
32％facetedclastsinsamplesof50．
Thefansarelarge（c．80mhighand250mwide）

1ations（basalglacial，Supraglacialand glaciofluvial
accumulations of sand and gravel located at thesediments）attheglaciermargin（seeinterpretationof
mouthsoftributaryvalleys．Thelargestofthefans，atStageTwosandybouldergravel，above）．Thesandy

fluvialdepositonthebasisofitssorting，Clastround−posedofalocallycrudely−beddedtowell−SOrtedsandy
nessandabsenceofstriatedandfacetedclasts（Glas− CObble gravel．Itis textural1y variable but typical
proportions are gravel（80％）and sand（20％）．Lith−SerandHambrey，2002）．

0logicalcounts（n＝200）show that the gravel・Sized
Clasts comprise schist（86％）and granite（14％）．The
StageThreemorainesreflectaglacialadvancewhichgravelTSized clasts are subrounded（78％），rOunded
WaSreStrictedtotributaryvalleysandlargecirques．
（16％），Subangular（4％）arld wellrounded（2％）．The
Whilsttheageofthiseventisnotclearasyet，WeCan
largestgravel−Sizedclastshaveb・aXeSOfuptoO．5m．
speculate that it represents a significant climatic
The kame features，located on the valley floor，
deteriorationduringtheHoloceneortheLate−Glacial．
arelow（c．7m high），elongated（c．15m diameter）
In the Leones valley to the south，thelarge glacial
mounds of sand and gravel．Sections throughthe
morainedammingtheeasternsideoftheLagoLeones
kamesshowwell−Stratifiedunltscomposedofvariablehasbeendatedto c．3000yearsBPusingOSLdating
amountsofsandsandgravels．Inmanycasestheunits
oflacustrine sediments5m below the crest of theShowevidenceofpost−depositionalfaulting．
moraine（Haresign et al．，unpublished data）andit
WOuldbesurprisingifsuchaclimaticeventwasnotJ〃んリpハイ（J／んりJ
representedinothervalleysdrainingtheicefield．
The landforms and sediments associated with・ノ．」．5／噸■t、爪）J′クーg／（J（、南／血〃イ／i）川ト′肌砧＝石肌川刑如−

ム肋朗椚那Stage Four depositionallandformsinclude

moraines；drift hummocks；bedrock−COred ridges；

1argefansandkames，andtheirassociatedsediments（Fig．5）．Theseareconcentratedinanarealr2kmto
the west，SOuth and east of Lago Tranquillo．Since

theselandformsandsedimentscover alarge area ofthelandscapetheyaredescribedherecollectivelyasa

morainic surface ．The morainic ridges are verybroadwithlow relative relief andwithan absence ofThe sandy boulder graveland sandy gravelare
texturallysimilartothosedescribedaboveaspartof

the Stage Three glaciallandform／sediment assem−

blage and are therefore similarlyinterpreted asice−
marginaldeposits and reworked glaciofluvialsedi−mentsrespectively．Thediamictonisinterpretedasa
basalglacialdeposit on thebasis ofclast roundness（subroundedandsubangularclasts），andthepresence
ofnumerousstriatedandfacetedclasts．Inaddition，it

is texturally similar to basalglacialdeposits de−
SCribedfromcontemporarytemperateglaciersofthe

HieloPatag6nicoNorte（GlasserandHambrey，2002）．

boulders on their surfaces．These deposits arerestrictedto below500metres above sealevel．

Thelargefanscomposed ofsand andgravelat
the mouths of tributary valleys are interpreted asJ〃J／J〃り上山

inthemainvalley．Evidenceforthisistheirposition

Naturalexposuresin the moraines，drift hum−mocks and bedrockTCOred ridges of the Stage Fourmorainic surface are rare and observations are con−alluvialfansdepositedadjacentto，OrOntO，glacierice

relativetothemainvalley，theirsedimentarycompo−
Sition（locally crudely−bedded to well−SOrted sandyCObblegravelwithsubroundedandroundedclastsand

finedtohand−eXCaVatedsections．Theseshowthatthe nostriatedclasts）．Sedimentologically，thesedeposits
morainicsurfacegenerallyforms athin（c．0．5−2m are very similar to those described from contempo−
rary glaciofluvial environments at temperate
thick，butlocally thickerin places）1ayer of sandy

gravel，Sandybouldergravelordiamictondrapedonagentlyundulatingbedrocksurface．Thesandygraveland sandy boulder gravel are texturally similar to
those described above as part of the Stage ThreePatagonianglaciers（GlasserandHambrey，2002）．

Thefaultedandbeddedsandandgravelsexposed
inthekamesdemonstratethattheyweredepositedin
anice−COntaCtenVironmentinassociationwithburiedglaciallandform／sediment assemblage．The massesofice．Theactivityofglaciofluvialmeltwater

4.3

Harrison（ヲJαJ．

StreamSissuggestedbythewell−beddednatureofthe
Sandandgravelunits．Suchsedimentassociationsare
typicalofthosefoundinproglaciallocationsinotherjn，AndyNelson，AngeloNunes−Gomez，KarenStraw

Winchester，1998）．

Antony Smith andIan Gulley of theInstitute ofPatagonian valleys（e．g．Aniya，1987；Harrison andAliGentleman，Richard Halliday，Mike Lee，Steve
Mahoney，WangPuiMing，DanMorrice，BramNawi−andCatherine Sweeney．The figures were drawn by

Collectively，theselandformsandsedimentscom− Geography andEarth Sciences，University ofWales，

priseamainvalleyglaciationevent．Tothewestandnorth of Lago Tranquillo，the valley glaciers haveproducedalandscapedominatedbyglacialerosionof
bedrock．The few driftlandforms developedin thiseasternsector ofthevalleycomprise Holocene allu−
vial and debris cones at the mouths of tributary

Aberystwyth．
Reterences

Anderson，E．，Harrison，S．andPassmore，D．G．（1998）：Geomor．
phic mapping and morphostratigraphicalrelationships：
reconstructing theglacialhistory of the Macgi11ycuddy sValleys．Theonlywell−developedmorainehereoccurs
Reeks，SOuthwestIreland．Bulletin of the Cartographic
near the present snout of Glaciar Exploradores andSociety，30（2）9−20．
thisisinterpretedhere asbeingyounger than Stage
Aniya，M．（1987）：Moraine formation at Soler Glacier，
Four．
Patagonia．Bu11etinofGlacierResearch，4，107−117．
Aniya，M．（1995）：Holocene glacialchronologyin Patagonia：
Tyndal1andUpsalaGlaciers．ArcticandAlpineResearch，
5．Discussion
27，311−322．
Aniya，M．（1996）：Holocene variations of Ameghino Glacier，NodatesareyetavailableinwhichtoplacethesesouthernPatagonia．TheHolocene，6，247L252．
Aniya，M．and Naruse，R．（1999）：Late−Holocene glacial
glacialstagesinto chronologicalcontextandwe areadvancesatGlaciarSoler，HieloPatag6nicoNorte，South
thereforeunabletoplacethemintoeitheraMercer・America．Transactions，Japanese Geomorphologicaltype or Aniya−Type moraine date scheme．We can，Union，20，69「83．
however，COmpare their morphologicaland spatial
Aniya，M．andShibata，P．（2001）：TheHoloceneglacialchronol−
Characteristics to those of moraines developed in
OgyOfRioSolervalley，HieloPatag6nicoNorte，Chile．InM．AniyaandR．Naruse（edi），GlaciologicalandGeomor−
Other valleysinthe reglOn．In many of the valleys
phologicalStudiesinPatagonia，1998and1999．67−83
drainingtheeasternsideoftheicefield，threeorfour
Glasser，N．F．andHambrey，M．）．（2002）．Sedimentaryfaciesand
distinctglacialstagescanberecognized．Forinstance，
landform genesis at a temperate outlet glacier：Soler
intheLeonesvalley20kmtothesouthofthestudy
Glacier，North PatagonianIcefield，Sedimentology，49（1）area，three major moraine systems are recognized（Harrison and Glasser，unpublished data）．On mor−

phostratigraphic grounds，and based upon their size

andpositionwithregardtothepresent・dayicefront，

these correlate with Stages One，Three and Fourdescribedinthisstudyanddisplaysimilarlandform／sediment associations．Further correlations between

themorainesequencesobservedintheExploradores
Valley and those from other valleys draining theicefieldwi11requirelarge−SCalemappingoftheglacial
geomorphologyoftheicefield．
Acknowledgments
ThisworkwasfundedbygrantsfromtheRoyal

GeographicalSociety（grantRGSO3／02）theQRAand

theUKNaturalEnvironmentResearchCouncil（grantNER／B／S／2002／00282）．We thank RaleighInterna−

tionalforfieldlogisticalsupportinChile．Weextend
OurthankstothefollowlngpeOpleatRaleighInterna−
tionalwho provided field assistancein March／Apri1

2003：Esther Baker，Ruth Creamer，Lucy Dickinson，

43−64．

Glasser，N．F．，Hambrey，M．J．andAniya，M．（2002）．Anadvance
OfSolerGlacier，NorthPatagonianIcefieldat c．AD1222
1342．TheHolocene，12（1）113120．
Haresign，E．，Winchester，V．，Warren，C．R，and Harrison，NeoglacialhistoryofGlaciarLeon，ChileanPatagonia：theSignificance of calving dynamics．Globaland PlanetaryChange（submitted）．
Harrison，S．andWinchester，Ⅴ．（1998）：Historicalfluctuations
Of the Gualas and Reicher Glaciers，North Patagonian
Icefield，Chile．The Holocene，8，481−485．
Harrison，S．and Winchester，Ⅴ．（2000）：Nineteenth− andTwentieth−Centuryglacierfluctuationsandclimaticimpli−
CationsintheArcoandColoniaVal1eys，HieloPatag6nico
Norte，Chile．Arctic，AntarcticandAlpineResearch，32，55
63．

Harrison，S．（2003）：The Pleistocene Glaciations of Chile．InEhlers，J．and Gibbard，P．（edi）Quaternary Glaciations：
ExtentandChronologyINQUA，EIsevier，89−103．
Winchester，Ⅴ．and Harrison，S．（1996）：Recent oscillations of
theSanQuintinandSanRafaelglaciers，PatagonianChile．
GeografiskaAnnaler，78A，35−49．
Winchester，Ⅴ．，Harrison，S．and Warren，C．R．（2001）：Recentretreat of Glaciar Nef，Chilean Patagonia，dated byli−
Chenometry and dendrochronology．Arctic，Antarctic andAlpineResearch，33，247¶252．