BulletinofGlaciologicalResearch22（2005）121−133

J2J◎JapaneseSocietyofSnowandIce

A34−year−longrecordofmassbalanceandgeometricchangesoftheDjankuat
Glacier．Caucasus

VictorV．PopovninlandRenjiNaruse2

1Cryolithology＆GlaciologyDept．，GeographicalFaculty，MoscowStateUniversity，LeninskiyeGory・Moscow・119992，Russi

2InstituteofLowTemperatureScience，HokkaidoUniversity，Sapporo，0600819Japan（ReceivedOctober15，2004；RevisedmanuscriptreceivedNovember30，2004）

Abstract

Dynamics ofmassbalanceanditscomponentsofthe DjankuatGlacier，repreSentativeforthe

CentralCaucasus，during the34−yearTlongperiod ofdirectmeasurementsareanalyzed・Mean massbalanceisslightlynegative卜160mmw．e．），Withaverageaccumulationandablationvaluescomingto
2410and−2570mmw．e．，COrreSpOndingly．Asaresult，OrthogonalprojectionoftheDjankuatGlacierareaonthenorthernmacro−SlopeoftheMainCaucasusRidgedecreasedby12％intheperiod1968−
1999，Whileitssurfaceloweredslightlylessthan6m（inwaterequivalent）．VariabilityofbothmassbalancecomponentsispracticallythesameattheDjankuatGlacier．Massbalanceextremescoincide

withtheyearsofmaximaofitscomponents・Thewhole34−year−longobservationperiodismarkedby
weaktrendstowardsincreaseofbothbalanceconstituents．Dominanttendencytowardstheimprove，
mentoftheDjankuatGlacierbudgetconditionschangedtothecontrary（or，atleast，WaSinterrupted）

since1998．Itis not clearwhetherthispatternindicates the beginning ofthe new stage ofglacierdegradationin theCaucasusoritshouldberegardedonlyasanaturalfluctuationofatmospheric
PrOCeSSeS．

1．Lntroduction
TheDjankuatGlacier，locatedintheCaucasus，iscurrentlythemostwidelyinvestigatedglacierinRus−

sia．The World Glacier Monitoring Service has se−

Adylsu va11ey，engraftedinto the northern macro−slope ofthe meganticlinorium．The Adylsu River，in
itsturn，isanimportanttributaryoftheBaksanRiver，
which belongs to the Casplan Sea basin．The upper−

most part of the va11ey，tOgether with the studied

glacier，facesNW．It hasatyplCalalplneappearanCe，
1ecteditasoneofthelOreferenceglaciersoftheEarthwithalotofsurroundingpeaksexceeding4000ma．s．1．
fortheglobalmass−balanceprogramme．Directobser− The extensive glaciation（Fig．2）is thecharacterisl二ic

vationsherehavelastedcontinuouslyfor34yearsup
to present．Thisis thelongest time seriesin Russia

featureoftheregion．

Morphometrically，theDjankuatGlacierhasmuch

andthesecondintheex−USSRterritory，yieldingonly incommonwithahypotheticalpatternofthetypicaltotheTuyuksuGlacier；besides，Djankuathasoneof
Caucasianvalleyglacier．Itlieswithinthealtitudinal
thelongest records a1lover the world．This mass
span2700−3750m a．s．1．anditis3．5kmlong，being
characterized by a step−1ikelongitudinalprofile．ItsbalanceseriesistheonlyoneintheCaucasussuitable
for tracing present evolutionary tendencies．Conclu−
physicalareais3．009km2，StatuS1999．Ingeneral，its
sions，derived here，COuld be extended to the entire ablationandaccumulationareasoccupythe2700−3020
centralsectionoftheGreatCaucasus，becauseinitiallymand3300−3600melevationrangescorrespondingly，

Djankuathasbeentherepresentativeglacierforthis
reglOn Since theInternationalHydrologlCalDecade（IHD）（TheDjankuatGlacier，1978）．

2．Generalcharacteristics of the Djankuat Gla−

Cier

Djankuat（Fig．1）issituatedin theaxialpartof

theMainCaucasusRidge，intheupperreachesoftheand thefirnlinemigrationbeltliesin between．Steepslopes above3600m a．s．l．are mainly represented byfirn／icerevetmentaroundthenotlrishmentbasin．
Djankuatis a typICalsimple valley glacier，COn，Sistingof4adjacenticestreams：tWOprincipalstreams
originate from under Mt．Gumachiand from the
Djantuganfirnplateau，andtwosecondaryonesflow

down from the slopes of Mt．Uya−tau and Mt．Djantu−
gan．Theindividualpeculiarityofthe DjankuatGla−

ノ22

Bu11etinofGlaciologicalResearch

Fig．1．A）TheDjankuatGlacier：generalviewoftheglacier（phototakenbyA．A．Aleynikovin2000）．

w華E

1 0 1 2 3 4 km
払■■Fig．2．Glaciersoftheinvestigation area（CentralCaucasus）．ASTERsatelliteimageof16．09．2001．TheDjankuatGlacieris
Shownbyarrow．

Popovninetal．

ト、涙．1．I引l）iヾitこ11t（、rIIこIiIll11川It−lいr111t、l）Jmlltし1こItし；】こ1し・i什Cier morphologylS theinitiation of one of the mostprominent and significant central ice streams from

This allowed to submit mass balance calculation re−Wards both northern and southern macro−Slopes of

SyStem aS Well．Approximately at the same time aprlnClpleofdrawingaccumulation，ablationandmassbalancefields wasintroducedinto practice of glaci−
OloglCalresearchattheDjankuatGlacier．Thesefields

the crestalfirn plateau，distributing massfluxes to−
the Great Caucasus．Theice dividelocation on theplateau surfaceis quiteindefinite，itis not clearly
pronouncedin theglacialreliefand continuously mi−
grates along theflat plateau．A specialinvestigation

byAleynikovetal．（2002）revealedtheDjankuatcatch−ment areaon theplateaucontinuously changing thr−

Oughout the entire34−yearTlong observation period，
averaging from O．300km2in1968▼1984，0．223km2in
19841992，0．243km2in1992−1998and O．387km2since
1999．

Djankuatisatemperateglacier，andthedominant
ice formation mechanismis the temperatefirn one（Shumskii，1964）．Itslocation within the zone ofrelar

tively humid climate determines the intensive mass
turnover，WiththeorderofmagnitudeofseveralthouT
Sandmillimetersofwaterequivalentperyear．
3．Mass baIance caIculation scheme

From the very onset of the continuous monitor−
ing at the Djankuat Glacier，maSS balance bn andits
components were calculated in accordance with theStratigraphic reporting system，aCCumulation being
represented by winter balance bw and ablation by
Summer balance bs．Since thelate1980s this scheme
turned to be closer and closer to the most sophisti−

Cated system−the combined system，Which requires
muchmoredetailed（frequent）measurementsin tran−

Sitionalperiods，Separatingbalanceyearsortheirsear
SOnS When accumulation and ablation processes canproceedsimultaneouslyindifferentaltitudinalspans．

SultsnotonlylnaCCOrdancewiththetraditionalstra−

tigraphic reporting system，but with thefiⅩed−date

WereSubsequentlydigitizedina50×50mrectangulargridin ordertocomputeexternalmass turnoverpa−
rameters for the entire glacier．Introduction of thedigitizingscheme andotherslightinnovationsdidn

affect the statistical uniformity of the balance timetSeries．Comparisonofmassbalancevalues，Calculated

forthesameyearbytheformerandthenewschemes，Showed that the difference didn t exceed 4％ as anaverage．That s why allconclusions about the ol）−

SerVed changes seem to be climate−related and not
CauSed by differenceinmethods．
TheaccumulationfieldattheDjankuatGlacieris

drawnonthebasisofdataobtainedat300L400（some−times more than500）measurement points of direct
SnOW depth survey，distributed more orless evenly

OVerthewholeaccessiblearea，COVeringca．90％ofthe
glacier ssurface（Fig．3a）．Snowdensityisestimatedin

4L5snow pits，dug both on the snout andin thefirnbasin，and extrapolatedlater over the entire area（）fthe correspondentglacierbelt．Snow depthsurveyis

Carried outin May，June，COinciding with the time of
SnOW maXimum．However，dates of maximum snow

accumulationin thelower and upper parts of theglacier usually differ byl．52months．Thatis why

SpeCialamendments，COuntingforaccumulationafter

the survey or ablation prior toit，are alsoinserted．
Seasonalsnow accumulation oninaccessible zonesis

Calculatedwiththehelpofgeographicalindices（suchBulletin ofGlaciologicalResearch

ノ24

0

500

1000

1500 m

Fig．3．a）Mass balance observationalnetwork at the Djankuat Glacier（status1999as an example），for accumulation
measurements：1−meaSurementpOintsofsnowdepthsurvey；2−SnOWpitsfordensimetry；3−borderoftheDjankuat
GlaciercatchmentareaontheDjantuganPlateau．

asabsoluteelevation，Slope，Surfacegeometry，aSpeCt， ternalfeeding （or ablation decrement），being based
dynamics oftheseasonalsnow melt−0ff，etC．）and sta−
on simulation results or indirect considerations andtisticalcorrelations between the grid nodes，looking
rather stablein time due to temporalconformity oftheaccumulation patternovertheglaciersurface．
Ablation atthe DjankuatGlacierismeasured byevaluated after a thorough examination，introduced

The usualablation network consists of50−80stakes

SnOWline dynamics and data of autumn（August−
September）snow depth survey．The threefields are
Strictly correlated with each other，SO that conse−means of the well−known method of stakes and pits．
（Fig．3b），meetingtherequirementsofthefirstclassof
reglmeObservations．Besides，meltingln thenourish−
mentareais estimated as a difference between snow−

pack water equivalents，meaSuredin spring andin

in former publications（e．g．The Djankuat Glacier，
1978）．

Mass balancefield results from the sum of accu−

mulationandablationfields，COrreCtedbymapplngOf

quentlytheequation
わ蝕＋∂5＝∂乃autumn．When drawing the ablation負eld，theinfluT iskeptvalidineachnodeoftheregulargrid．
ence of debris cover on thawing rate（Popovnin and
The 負nalcalculation of overa11glacier budget
Rozova，2002）isalsotakenintoaccountaswellasen− parameters is carried out by averaging values notand subglacialmelting，ablationin crevassesand in−
ObtaineddirectlyinmeasurementpointsbutdigitizedPopovninetal．

0

J25

500

Fig・3・b）Mass balance observationalnetwork at the Djankuat Glacier，forablatior］meaSurementS：1−ablation stakes

anditsnurrlbers；2−referencecable；3−borderofthedebriscoveron theglaciersnout；4−borderoftheDjankuat
GlaciercatchmentareaontheDjantuganPlateau．

inthegridnodes・Hereby，theinfluenceofsubjective 1994）concerned the observation periodbetween1968

arrangementofanydirectmeasurementiseliminated，
and the resultant data set becomes statistically slgTnificantandindependent．

4．StatisticaJstructureofmass baJance timese−ries

Results of accumulation，ablation and mass bal−ance calculation over theinstrumentalobservation
periodaresummarizedinTablelanddepictedonFig．
4．

The dynamics of mass−balance features of the
DjankuatGlacierthroughout34yearsofdirectmeas−

urements has not yet been analyzed before．Previ−

andtheearly1990s，Whereastimeseriesexceeding30
yearscandisclosepresenttendenciesinexternalmass

andenergyturnovermorereliably．Thisdurationre−

flects animportant quantitative thresholdin statis−

tics，ingeneral：ifatimeseriescontains＞30items，jts

Variability can be evaluated by nonLShifted disper−
Sion．

Negative mass balance values prevailed during

the34−yearTlong observation period，and are regisT
teredin19years．Themeanlong−termmeanValuesof
accumulationandablationare2410and2570mmw．e．，

COrreSpOndingly，makingupanaveragemassbalance

Value of−160mm w．e．The rangein accumulation

Valuesis2350mm，With a standard deviation of420

OuSlypublishedsummaries（e．g．BaumeandPopovnin， mm．The rangein ablation valuesis aboutl．5times

Bu11etinofGlaciologlCalResearch

J2∂

4 0
0
︵
0
．
0
甲
き
∈
∈ 2 0
︶
0
u
O
葛
一 1 0 0
⊃
∈
⊃
0
0
e
P
u
e
￠ 0 0 10
2
﹄
眉
∽
の
2 00
巾
0
∈
ビ
○
00
焉
0
一
月
く

1967／681970／711973〝4 1976／77．1979／80198ガ831985／861988／89 1991／921994／951997／98 2000／01

Balance years
Fig・4・Accumulation，ablation and mass balancefluctuationsofthe DjankuatGlacierduring the34Tyear−long periodof
direct measurements．

Smaller（1670mm），With a strongly higher standard
deviation of470mm．Variation coefncientcv of accu−

mulation（calculatedasstandarddeviationdividedby
the mean）is also slightlyless than that of ablation−0．17against O．18．During the1968−1974（IHD）period
CuOfaccumulationwasO．10，Whereascl，Ofablationwas
twice as high（0．21）．Later，however，the20−year−longtoalmostcompletelackofcorrelation between them．
In other words，the amount of winter snowis foundOut nOt tOinfluence the summer thawing．Allthis
demonstrates the specialimportance of the observa−
tionperiodduration：Shorttimespansleadsometimes

to unreliableconclusions，nOtCOrrOboratedlateron．

timeseriesrevealedalreadyaquitedifferentrelation−

Mass balance variationis muchhigherthan that
Of any ofits constituents：the range ofits annual

WaSOften characterizedbybothincreasedaccumula−

COrreSpOndstothemostnegativemassbalancevalue

Ship：Ct，OfaccumulationbecameO．20andcvofablation
Valuesis2680mm w．e．and the standard deviationis
becameO．18（Popovnin，1989）．Hence，thetendencyto− 650mm．Thelatteris somewhat higher than for theWardslevelingofaccumulationandablationvariation
IHD period（580mm），thoughit yields to that of theWithtimecan beeasily traced．Apparently，Variation
first20years（680mm）．Itispeculiarthatmassbalance
Of mass balance components would remain approxi−
Valueismostlypredeterminedbyablation：itscorrela−matelythesameinthelong−term timescale．
tionwithaccumulationr（b軌bn）＝0．70isslightlysmall−
Formerly，When analyzinglO−and20−year−longer than that with ablation r（bs，bn）＝0．77．Balancetime series（Chizhov，1982；Popovnin，1989），the bal−
extremes coincide with maxima ofits components：
anceeffectcausedbyaccumulationandablationano−
the highest accumulation，Observedin1986／87（4000malies was revealed tocoincide：forexample，ayear，
mm w．e．）answers the balance maximum（＋1540mm），
markedbyfavourableconditionsfortheglacierhealth，
Whereas the highest ablationin1999／2000（3630mm）
tion and reduced ablation．Nevertheless，analysis of （−1140mm）．
the34−yearTlong seriesleads to the opposite conclu−
The high degree of temporal steadiness of theSion：low correlation coefncient between annualval−
externalmass／energy turnoverfields resultsin theuesofaccumulationandablationr（bw，bs）＝0．07testify peculiar pattern：localaccumulation，ablation andPopovninetal．

上27

Tablel・Results of the Djankuat Glacier mass balance monitoring（in mm of water equivalent）
duringtheperiodofdirectobservations．
Balanceyear
1967／68
1968／69

1969／70
1970／71
1971／72
1972／73
1973／74

1974／75

1975／76
1976／77
1977／78
1978／79
1979／80
1980／81
1981／82
1982／83
1983／84
1984／85
1985／86
1986／87
1987／88
1988／89
1989／90
1990／91
1991／92
1992／93
1993／94
1994／95
1995／96
1996／97
1997／98
1998／99

Winterbalance Summerbalance Massbalance，（accumulation），
b札，mm W．e．

（ablation），bs

2060
1890
2410
2400
2170
2200

mm W，e．

0
0

︻

0

0

一
一

0
0
0
0
0

O

O

0

O

7 2

O
O

2

O

0 2

O
n
︶

1

6

7 0

8
0
6

2390

1

5

8

9 3

2
9

一
一

3
1

7

2
3
0

2270

0

1820

6

1

0
4
6
ハ
U

1

2
9
8

2620

8

2490

2

2660

9

2480

9

1950

6

▲

14

1
0

4

4
4

7 5

3
4

6

︹9
古0

9
0
3
4

一
一
一
一

1
0

6

7 3

9
5
1
0
0
・
4

7 2

3
1

5

6
0

9 6

2
7
4

7

1

0 9
l
0 9

■
4

2540

l

3
7

2430

0
0
9

一

2

5

7 2

4
5
5
9

5

8 2

6
0
1
2
2

7 1

2
3
2

1

2

9 0

3

mass balance extrerneS are eVery year Observed al−
mostatthesamesitesoftheglaciersurfaceirrespec−
tiveoftheabsolutevaluesofcorrespondingparame−
tersforthewholeglacier．Theonlyexceptionsarethe

beltofsteepfirn／iceslopes，Whereaccumulation val−uesarecorrelatedweaklywiththebackgrounddueto
the active gravitationalredistribution ofthe matter，and thelowermost part of the snout，Where annual
ablation depends prlmarily on winter snow amountthatdetermines the duration of thepartofthesum−
mer season when the exposed supraglacial debris
COVerplaysitsscreeningrole．
5．Trendsin mass balance

Each of34−year−long time series of budget paTrameters（accumulation，ablation，maSS balance）has

1
2
2
2
2
3
2
2
2
2
2
2
2
2
2
2
2
2
2
2
2
2
3
2
3
3

2

8 7

5

一

8

∩7
プ6

2

2240

2410

9 5

O

2780

Average

4

2 2

0
︵
U

2520

2490
2420

8 2

0

O

1999／2000
2000／01

3

0

O

2810

8 6

0

2560

2270

1

0

∩
︶

2140

2540

0 0

0

O

2070

9

0

O

3180

5 5

0

2220

4000

run−0ff，

106m3aゝ1

0

2180

1650

mm W．e．

Glacier−derived

0

一
一

2360

2530

bn

itsownpeculiarfeaturesthroughouttheentireperiod■

Ofdirect observations．

7

4

0

Aweaklinearlyincreasingtrendcanbedetected
7 1

1
On Fig．4for the accumulation series．Itis
not very9
Wellpronounced，judging byits 9R2−Criterion
value
0（0．0783）．Thesameisvalidalsoforablation（orsummer
8 5balance），reVealing a very slight trend
towardsin−
3
8 4
CreaSe Ofits absolute value（R2＝0、0776）．Dominant1
8 −tendencyinmassbalanceseriesin1968−2001ispracti−
3
Callynon−prOnOunCedatall（R2＝0．0005，thatisstatisti−
1 9
4
Callyinsignificant）：Weakincrease
ofaccumulationis
9 0
almostcompensated by weakincreaseofablation．
0

The accumulation time series can
0 8 be subdivided
intoanumberofstages：
4∩1，Stagel（1968−1977）：Accumulationisalmoststa−
プ6
ble（cu＝0．07），anditaverages2200mm；
1−Stage2（1978−1982）：Mean accumulation
value
4
9
1

BulletinofGlaciologicalResearch

J2βincreases abruptly up to2560mm w．e．，thelow varia− the mean mass balance value suddenly decreasedtion remainingatthesamelevel（cl／．＝0．07）；
down to−830mm．
−Stage3（1983−1986）：Accumulationvaluesarethe
Signs of56year cyclic recurrence can be de−lowestofthewholeobservationperiod（2000mmatan
tected for accumulation records within the34−year−
average），itsinter−annualvariationgrew rapidly
long period underinvestigation．The most vivid fea−
ture of the ablation seriesis biannualharmonic，eX−（c王ノ＝0．15）；
T Stage4（19871993）：Thisis a time span of thepressed best of allin1968−1985and attenuated afteト
highestaccumulation（themeanvaluecomingto2770
Wards；78year cycles can be traced also．Biannualmm）and thegreatestvariation（c，ノ＝0．24）；
CyClicity stands out also for the mass balance series，−Stage5（1994−2001）：Thefinalstageischaracterr
PrOnOunCed even betterthanfortheablation series．

ized by the reduction of both accumulation and its
variation．

6．Discussion of mass balance trends−Stagel（1968−1981）：Ablationslightlyexceedsits
long−termaVerage（2560vs．2570mm），anditsvariation
is high（cL，＝0．19）；Only two episodes of considerably

月uctuationsinamoredetailed way，payingattention

A similar subdivision of the ablation time series
intostageslooksasfollows：increased ablation take placein the early1970s andearly1980s；−Stage2（1982L1993）：Both absolute ablation va−

1uesandtheirvariationbecomesmaller（2330mmand

Cu＝0．12，COrreSPOndingly）；−Stage3（19942001）：Thefinalperiodis themost
peculiar，because ablation reachesits absolute maxi−
mum（averaging2590mm），aCCOmpaniedbythegrowth
Ofinter−annualvariation（c．，＝0．16）；the verylast 4
years，1998−2001，Werethemostoutstanding，Sincethis

WaStheonlytimespanthroughouttheentireobserva−
tion period at the Djankuat Glacier，When ablation

Let us discuss now the reasons of mass balance

to the mostgeneralclimaticprerequisitesduringthe
pastperiods．
In19681986mass balance wasinfluenced mostly

by ablation and not by accumulation：r（bs，bn）＝0．87，
Whereasr（bzp，bn）＝0．60．Asawhole，thistimeinterval

WaS Characterized by moderate amount of winter
SnOWthatincreasedalittleduringthelasthalfofthe
Period．SummertemperaturedidnotdiscloseanyproT
nounced trendoverthis timespan．

The1987−1997stage wasquiteinverse：r（bs，bn）＝0．53and r（buノ，bn）＝0．91，meaning that mass balance

WaS determined mainly by accumulation．The mainfeature of this stage was the growth ofwintersnow

amount．Simultaneously，Summerair temperaturein−practica11y exceeded3000mm w．e．during4consecu− CreaSed also，nOtWithstanding the fact that ablation

tiveyears．

Fluctuations of glacier−derived bulk run−0ff（Ta−blel），thatis，maSSloss（in water equivalent）multi−
Plied withtheglacierarea，naturallyinheritfeatures，
peculiar for the ablation time series．However，they

Wereinfluencedtoacertaindegreebyarealreduction

period used tostartsomewhatlaterthaninprevious
yearS．

Since1998practically functionaldependence be−

tween mass balance and ablation r（bs，bn）＝0．99isObserved，thoughapparentlyonecannotspeakofany

Statisticallyslgnificanttrendforsuchashort，4−year−
OftheglacierofmorethanlO％．Therefore，thegeneral long timeinterval．Nevertheless，at the same timedecreasingtendencyfortherun−0ffisexpressedquite

SOme nOteWOrthy features of this short stage should

as the averageforthe whole34Tyear−longperiod waspatently atypical not only for the Djankuat Glacierdefinitely．The only exception occurredin1998−2001， be noted．Forinstance，a unlque phenomenonis tra−When considerablyincreased ablation caused thein−
Ced：interrelationshipbetweenmassbalanceandaccu−
CreaSeOftherunningmeantolO．2×106m3a】，Where−
mulation becameinverse −r（bw，bn）＝−0．76 − thatis

evaluated as8．7×106m3al．

Themassbalancetimeseriesispredeterminedby

butfortheEarth sglacierizationentirelyaswell（e．gl
Chizhov，1982）．Directlyobservedalterationsinmacro−tendencies，reVealedseparatelyforeachofitscompo− CirculationpatternsovertheGreatCaucasussincethe
nents，but hasits own peculiarities as well，Since at beginningof19981edtothecertaindecreaseofwinterdifferentstagesitisinnuencedmainlybyeitheraccu−

SnOWamOuntandsharpsummerairtemperaturerise．

The absolute air temperature maximum，eVer re−balance value was considerably negative 卜370mm
COrded at the Campsite weatherstation800m below
W．e．）．Between1976and1986thebudgetconditionsof the Djankuat Glacier terminus，increased by more
theglacierrelativelyimprovedattheexpenseofaccu−
than20c after early1990s．Summer precipitation re−mulationgrowth，thoughitsaveragevalueremained
duced considerably：e．＆Only2short periods of rain
negative（150mm）．Much more pronounced was thisWere registeredin August1998，bringlng15mmin
improvementin1987−1997：the average value obviT
total，Whichisonlyca．20％ofthelong−termClimatic
OuSly movedinto thelield of positive values（＋220
mean．
mm w．e．）．However，this stage was followed by the
However，in spite of the evidentpeCuliarities ofmulation or ablation．In1968−1975 the mean mass

extraordinarilyunfavourableperiod，andin19982001

thelast4years，the mass balance of the Djankuat

Popovninetal．

J2タ∈∃ lll■

′）
3

2

7

0

500

1000

4

1500 m

Fig．5．Changesin the Djankuat GlacierlOOmintervalcontourlines andits boundaries
in19681999：1−arealloss；2−arealexpansion；3−COntOurlinesin1968；4−COntOurlinesin1999．

Glacierseems to revealno decreasing trend over themeansoflOmisohypseswerecompiled asaresultof

Outthewholeperiodunderinvestigation．Atthesame
time theslightincrease of both balance components
by absolute value mean the gradual increase of thetotalmass turnover and of the glacier energy．The
glacier reglme tends to the pattern，anSWering more

ragingmeasureddistancesbetweenapairofadjacent

Whole34−year−longperiodofdirectmonitoring．Trend− terrestrialphotoLtheodolite surveys，undertakenin
1ines，depicted on Fig．4，demonstrate evidently that 1968，1974，1984，1992，1996and1999．Areas were esti−
theglaciercanbeconsideredquasiTStationarythrough−mated，and mean slope values were derived by ave−maritime conditions．Future measurements wi11clari−fywhetherthefinalpost−1997stageslgnifiesachange
into an increasingly more negative mass balance

trend orifitis a normal（casual）short−termfluctu−
ation．Anyway，the most recent years（after2001）of

massbalanceestimates havenotyetbeencalculated（rawfield data arestillbeingprocessed），but prelimi−

nary observations seem to testify in favour of thelattersuggestion，because the weatherconditions be−

Came prOfitable for the glacier agaln，and summers

2002and2004，inparticular，WereeXtremelycooland

humid fortheentirealpinebeltoftheCaucasus．

7．ChangesofthegJaciergeometry
Themainconsequenceofaglaciermassturnoverisalwaysthechangeofitsarealandspatialextentas
Wellas altitudinalalteration ofits surface．In order to

Obtainthedetailedandthoroughestimationofchanges

in glacier geometry，SixlargeTSCalel：10，000maps of

the Djankuat Glacier with the relief depiction by

lO−misolinesin every node of the regular50×50m

grid．The monitoring programme alsoincluded an−

nualdeterminationoffrontalfluctuationsalong8lon−

gitudinaltransects．Atthesametimethestereophoto−grammetricalmethod providedanindependentaccu−
racycontrolofmassbalancecalculations．Table2andFig．5show how thespatialpositionoftheDjankuat
Glacierhaschanged between1968and1999．
Inordertounderstandthecharacteroftheglacier
response to the climatic signalitis better toexclude
Djankuat catchment area on the Djantuganfirn pla−
teau，Whose dynamicsis predeterminedlargely by a
COmplicatedmechanicsofdivergenticeflow．Thenthe
OrthogonalproJeCtion areaoftheglacieronlyonthe
northern macro−Slope of the Main Caucasus RidgeturnsouttohavedecreasedbyO．323km2，Orabitless
than12％，duringthisperiod．Themostextensivearea

reduction occurred between1968and1974，thenits
rate gradually decreased and accelerated again after

1992．Changesofthe totalDjankuatGlacierarea，in−

CludinglCeCatChmentareaontheplateau，arelargely
influenced by the process ofice divide mlgration，describedinSection2．Fromtimetotimethisprocess
eithercausestheintensifiedreductionofthetotalarea

Or，Vice versa，COmpenSateSareallosseson thenortll一

Bulletin ofGlaciologlCalResearch

JJりTable2．ArealreductionoftheDjankuatGlacier（excludingtheDjantuganfirnplateau）during1968

1999．

Parameter

1968 1974

1984

Physicalareaoftheglacier，km2

3．034 3．039

Meanslope，degrees

23．1 28．3

OrthogonalproJeCtionarea，km2

2．790 2．676

ReductionoforthogonalproJeCtionarea，km2

0．114

AnnualrateoforthogonalproJeCtionareareduction，
km2a1

ern macro−Slope．Nevertheless，the generalresultant

effect over34years of direct monitoringlS the de−creaseofthetotalglacierareafrom3．234to3．009km2，
Orby9．3percent．

Changesofaglacierareaatprogressiveorregres−Sive stages ofits evolution are traditionally consid−
ered to occur mainly at the expense offrontalvaria−

0．019

1992

1996

1999

2．913

2．816

2．767

24．4

25．1

2．653

25，4

2．549

2．740

25．8
2．499

0．079

0．048

0．050

0．008

0．006

0．012

2．467

0．032
0．011

35m（Zolotaryov and Popovnin，1993）．In1985theterminusretreated2mmore，butafterthestableposi−
tionin1986it re−advanced by3min1987，rumplingand destroying the new−born moraine．Thenit re−mainedin a quasi−Stationary position until1993（e．g．

in1991itretreatedbylmandin1993re−advancedbylm），butitresumeditsretreatsince1994．Thefrontal

OfdirectobservationstookplaceJuStneartheupper−
most boundaries of the DjankuatGlacier．More than75percentofarealreductionoftheglacierfallsonthe

recession reached9m during the next3yearsand17
m moreduring19961999．
In these years the terminal retreat took place
predominantly at the expense of its orographicallyright periphery．Recession of theleft and thecentral
parts ofthesnout wasrestrained by thethickdebris

basin．Thisisexplainedbythefactthatice thickness

shifted towards the central part of the front that

Valuesrapidly compels this thiniceenvelope tomelt
Offcompletely．Thisprocess becameespecially active

toterminalretreatalongthewholefront．In2000thisand stones collapsed from the crestalsection of sur−roundingmountainswithanincreasedoccurrence．Ice

thedynamicsofarealchangesinablationzoneofthe
glacier．During the regressive phase of the glacierevolution the debris cover expands，anditis thisexpansion that governs prlmarily the mlgration not
Only of terminalbut oflateralglacier boundaries astions．The undertaken research shows that this state−mentisincorrect for brief time spans（from years tofirst decades）．Thelargest changes during the period

regionof且rn／icerevetmentaroundthenourishment

COVer．However，1ater the glaciers meltwater tunnel

hereistoosmall，itrarelyexceedslOm．Atthedegla− WaShedawaythemorainicdeposits，eXPOSedthesubL
Ciationstagetheprevalenceofnegativemassbalance
Strateiceontothedaysurfaceand，COnSequently，led
exceededlOm．Evolutionofdebriscoveron thesnout

Since1998，and consequently，tremendous rockfa11s turns out to be a very important process regulating

surface on the revetment above the firn basin of the

Djankuat Glacier diminished during1968r1999by afactorof7．Asimilarsituation，bytheway，1SrepOrted（Panov，1993）to have taken placebetween theendof

the19th centuryandthe1970sonmostoftheglaciersin the CentralCaucasus．
FluctuationsofDjankuat

ssnoutboundariesdu−

ring the period underinvestigation were not so dy−
namic：the contribution of areallosses around the

SnOut COntOurinto the totalreduction of the glacierarea comes to only15per cent．Usually，Variation of

the snout boundaryis characterizedfirstofa11byits
terminalfluctuations．Its totalrecession between1968
and2000waslO5m，but this process was extremely

Well．IfthelateralboundarylSrepreSentedbybareice，

it shiftsinwards with timein accordance with thedominant glacierdegradation tendencies．Butifmar−

ginalpartsofthesnoutarescreenedbyathicklayer
Of morainic materialthat reduces ablation，alateraladvance of the snout boundary can take place．This
expansionis engendered by theiceinflux from theupperglacierbeltsduetoitsviscousflow，Whichisnot

herecompensatedbyablationanymore．Forinstance，

theonlypartoftheDjankuatsnoutboundary，Where
areal expansion was observed during the period of
uneven．During theIHD，in1968−1974，the Djankuat directmonitoring，1SSituatedalongtheleftperiphery
Oftheglacieratanelevationof2710¶2880m a．s．1．The
Glacierterminusretreatedby60m，COrreSpOndingtoa
newrampartofmodernlateralmorainewithaheightmean annualrate oflOm a1（Golubev etal．，1979）．
Ofca．1．5−2mwasformedjustalongthissectionofthe
Later this velocity decreased：by the early1980s theglacier retreated28m more and subsequentlyit re−glaciercontour．
Anothersignificantpeculiarity ofglacio−mOrphoT
mained nearly stationary during a number of years．
logicalevolutionoftheDjankuatGlaciersnoutduring
Thispauseresultedinformationofthefreshterminal
morainelookinglikearampartwithaheightofabout
theperiodofdirectobservationisthesteadfastgrowth

Popovninetal．

J3J

Table3．Changesin the Djankuat Glacier surface elevationin19681999（after Golubev etal．，
1979；Zolotaryovetal．，1997；Aleynikov，2001）．

Meansurfaceelevationchange，mW．e．

1968−1974

1974−1984

−1．90

−0．88

12

40

Shareofglacierareawithhypsometricalrise，％19841992

19921999

0．36

2．77

48

12

N

L

500

500 m

0

」

■■▼r「「−m

I II lr■−32−28−24−20−16 −12 −8 −4 0 4 8
へ／1968

ハ／1999Fig．6．ElevationchangesoftheDjankuatGlaciersurfacein19681999．

not only of the supraglacial moraine area but ofdebristhicknesstoo．In1968thesupraglacialmoraine

in1983and19940Vertheentiredebris−COVeredpartof
theDjankuatGlacierandmappedminutely（Popovnin

duringtheprevalenceofpositivemassbalancevalues．
Comparisonofapairofdebristhicknesssurveys，held

PrOCeSSis particularly significant（reduction up to

COVeredO．104km2，Or3percentoftheglacierarea，and andRozova，2002），reVealstheincreaseofbothaverageby1999thesevaluesincreasedapproximatelythrice−debristhickness（26cmin1983and39cmin1994）anduptoO．293km2，OrlOpercentoftheglacier．Ingeneral，Values ofitslocalmaxima（183 and 280cm，COrre−
SPOndingly）．Such thicknessesoflithogenicenvelope
debriscoverexpansion rateisinverselyproportional
PrOmOte attenuation ofsub−debris thawing，and thisto mass balance：theleast arealincrement occurred25％）for thelowermost zones of the snout．The

／． ？ごBulletinofGlaciologlCalResearch

growthofsupraglacialmoraine，includingtheabove− tion，COmplicatedevenbyepisodesofre−advance．This
mentioned effect of recent intensification of rockfalls

Period seems to have ceasedin1997，becauseclimate

and stone collapses from the revetment of the firnbasin，1eads to hypsometricaldifferentiation of theinconsequentyearshardlypromotedconservationof

COVered stream of the snout，Whose substrateiceis

yearsslgnifythenewwhorlofresumedglacierdegra−

ice and water resources，StOredin theglaciersofthe

SnOutSurface．Nowadays，forinstance，theleft，debris− Caucasus．Itis not obvious sti11whether the recent
insulated from the exterior energyfluxes，tOWerSCa．

20r25mabovetheadjacentstreamsofthecleanice．
Alongsidewitharealchangesandterminalfluctu−

dationintheCaucasusoriftheyrepresentonlycasualfluctuation of the natural dynamics of atmosphericprocesses．A11the more，itis particularlyimportant

ations，areliableindicatoroftheglacierstateisaltera− nowtocontinuethecomplexmonitoringoftherepre−
tionofitssurfaceelevation（Table3）．During theIHD
Sentative glacier，uninterrupted since1960s，aS areli−

the predominantlowering oftheglaciersurface wasregistered．Afterwards，in1974−1984 and1984−1992，

differentiation of the Djankuat Glacier area by the
resultant hypsometricaleffectincreased essentially：
Surface rising began to be detected on considerable
partsoftheaccumulationareaandfirnlinemigration

ablebasisofjudgementsconcerningevolutionofthe
entireglacialsystemintheCaucasus．
Acknowledgments

TheresearchwasapartofaproJeCt Featuresof

belt．In19841992，partS Of the glacier area where PreSenteVOlutionofcontinentaland maritime moun−

Surface rise and surfacelowering were observed be−
Came apprOXimately equal．Alocalzone of surface

risingwasalsoformedonthesnout−alongitsdebris−
COVeredleftmargin．However，thefinaltimeinterval，
1992−1999，WaS marked by drastic reduction of theglacierareasharewheresurfacerisingtookplace．The
registereddecreaseoftheDjankuatGlacierthickness
OCCurred even moreintensively than during theIHD
period．
Asawhole，between1968and1999theDjankuat
Glaciersurfaceloweredalmostby6minwaterequiva−

tainglaciers，SuppOrtedbyInstituteofLowTempera−

tureScience，HokkaidoUniversity，Japan．Itwasalso
SuppOrted by the Russian Foundation of Basic Re−
SearCh（grant No．03−05−64973a）．The authors arein−
debted to D．Petrakov and A．Aleynikov for theirefn−
Cientparticipationinthefieldworkaswellasfortheirprecious assistance when preparing the manuscript．
Our specialthanks are to H．Jiskoot for her fruitful
Criticismandcommentsthatimprovedthepapercon−
Siderably．

References
1ent．Itslocalmaxima，i．e．sites with thelargest de−pression values，graVitated towards thelowermost，
Aleynikov，A．A．（2001）：Relationshipbetweenthemotionand
debris−free，partOfthesnout．Insomeofthesesitesthe
mass balance of an alpine glacier（Djankuat Glacier，
totalhypsometricaleffect reached−28m w．e．，Where−
CentralCaucasus，aS an eXample）．RhD thesis．Moscow，

asits mean value，aVeraged over the whole ablationarea，Came tO−10．5m．In丘rnline mlgration belt theSurfacebecameca．5mloweraswellasinthenourish−

24pp．（in Russian）．
Aleynikov，A．A，，Zolotaryov，Ye．A．and Popovnin，Ⅴ．Ⅴ．
（2002）：1cedividerecognitionontwinnedglaciers：aCaSe
Ofthe Djantuganfirn plateauin theCaucasus．Moscow

ment area and onfirn／ice revetment−4and5．3m，Univ．Herald，Ser．5 Geography （3），36−43（in Russian）．
COrreSpOndingly（Fig．6）．Discrete and area11ylimited Baume，0．and Popovnin，Ⅴ．Ⅴ．（1994）：Langzeituntersuchun−

Plots ofsurface rising aresitedfirst ofallbelow the
Djantugan Passin the nourishment area andin the

ZOneS Of continuous debris cover．The share of theglacierareawiththeresultantsurfacerisingafterthe

Whole34−year−longperiodislessthan13percent．

8．Conclusion
Inspiteofthefactthattheperiodofdirectobser−
Vationsat the DjankuatGlacierlastsnomorethana

third of a century by now（thatis too smallin com−
parison withthe glaciationlifein the Caucasus），thistime span embraces different phases of the present

glacier evolution．The stage of active deglaciation，

dominant up to thelate1970s，WaS fo1lowed by aperiod much more favourable for the glaciers in the
Caucasus，during which many glaciers considerably
deceleratedtheirretreatrateandsome，includingthe

Djankuat Glacier，Came tO the quasi−Stationary posi−

genzurBudgetentwicklungdesReprasentativgletschers
Dshankuatim ZentralenKaukasus．In：

PetermannsGeo−graphische Mitteilungen ，Gotha，Germany，138（5），273
286．

Chizhov，0．P．（1982）：Results of analyzinglong−term glaciermass−balance time series．Data of GlaciologlCalStudies，
42，170176（in Russian）．

Djankuat Glacier（1978）：Leningrad，Gidrorneteoizdat，184p．
（in Russian）．

Golubev，G．N．，Dyurgerov，M．B．andZolotaryov，Ye．A．（1979）：
Problemsofexternalmassturnoverofalplneglaciersat
deglaciationstage（apilotstudyoftheDjankuatGlacier）．
DataofGlaciologicalStudies，36，2533（in Russian）．
Panov，Ⅴ．D．（1993）：PresentglacierevolutionintheCaucasus．
Saint−Petersburg，Gidrometeoizdat，430p．（in Russian）．
Popovnin，Ⅴ．Ⅴ．（1989）：ThebudgetevolutionoftheDjankuat
Glacier，repreSentative for the CentralCaucasus．PhD
thesis．Moscow，24pp．（in Russian）．
Popovnin，Ⅴ．Ⅴ，and Rozova，A．Ⅴ．（2002）：Influence of sub−debristhawingonablation andrunoffoftheDjankuat
Glacierin the Caucasus．Nordic Hydrology，33（1），Lyn−
gby，Denmark，p．95110．
Shumskii，P．A．（1964）：Principles of structuralglaciology．
New York，DoverPublications．

Popovninetal，J∴？

rkovets，Ye．G．（1997）：TheDjankuat Glacierduringthe
Zolotaryov，Ye．A．andPopovnin，Ⅴ．Ⅴ．（1993）：Hypsometricallast25years．Moscow Univ．Herald，Ser．5 Geography
Changesofthe DjankuatGlacierafterI．H．D．（1968−1984）．
（1），24−30（inRussian）．
DataofGlaciologicalStudies，77，177−183（inRussian）．
Zolotaryov，Ye．A．，Popovnin，Ⅴ．V．，Goretskiy，A．S．andKha−