95

Bulletin of Glaciological Research ,. (,**1) 3/ῌ+*1
῍Japanese Society of Snow and Ice

Glaciological and geomorphological studies at Glaciar Exploradores, Hielo Patagónico
Norte, and Glaciar Perito Moreno, Hielo Patagónico Sur, South America, during ,**-ῌ,**/ (GRPP*-ῌ*/)Masamu ANIYA+, Hiroyuki ENOMOTO,, Tatsuto AOKI-, Takane MATSUMOTO.,
Pedro SKVARCA/, Gonzalo BARCAZA+, Ryohei SUZUKI0, Takanobu SAWAGAKI1,
Norifumi SATO2, Evgeni ISENKO3, Shogo IWASAKI+*, Hernan SALA/, Akira FUKUDA++,
Kazuhide SATOW+, and Renji NARUSE++ Graduate School of Life and Environmental Sciences, University of Tsukuba, Ibaraki -*/ῌ2/1,, Japan, Department of Civil Engineering Kitami Institute of Technology, Kitami *3*ῌ2/*1, Japan- Department of Geography, Kanazawa University, Kanazawa 3,*ῌ++3,, Japan. Faculty of Science, Hokkaido University, Sapporo *0*ῌ*2+3, Japan/ Instituto Antártico Argentino, Serrito +,.2, C+*+*AAZ Buenos Aires, Argentina
0 Graduate School of Environmental Studies, Nagoya University, Nagoya .0.ῌ20*+, Japan
1 Graduate School of Earth Environmental Sciences, Hokkaido University, Sapporo *0*ῌ*2+*, Japan
2 Kaihatsu Koei Co., Ltd. Kita ., Nishi /, Chuo-ku, Sapporo *0*ῌ***., Japan
3 Institute of Low Temperature Science, Hokkaido University, Sapporo *0*ῌ*2+3, Japan+* National Institute of Polar Research, Itabashi, Tokyo +1-ῌ2/+/, Japan++ Graduate School of Science and Technology, Shizuoka University, Hamamatsu .-,ῌ 2/0+, Japan+, Nagaoka National College of Technology, Nagaoka 3.*ῌ2/-,, Japan+- NPO, Glacier and Cryospheric Environment Research Laboratory, ,ῌ--3 Higashi-cho, Tottori 02*ῌ**++, Japan(Received October ,, ,**0; Revised manuscript acepted November ,,, ,**0)

Abstract
The major results of the Glaciological Research Project in Patagonia (GRPP) ,**-ῌ,**/, whichtargeted Glaciar Exploradores of the Hielo Patagónico Norte (HPN) and Glaciar Perito Moreno of the
Hielo Patagónico Sur (HPS), were reported. Studies at Glaciar Exploradores include recent glacialchronology, glacier ﬂow measurements with D-GPS, meteorological measurements with an AWS andhydrological measurements at the outlet stream. Three moraine systems were recognized, and mostrecent two of them were formed sometime between the +,th and +1th century and the early to mid-+3th
century. The annual glacier ﬂows in the area within / km from the terminus ranged .2 to +-2 m in ,**-ῌ,**.. Strong emergence velocity was observed near the terminus. The annual precipitation near theterminus was close to -*** mm, the mean annual air temperature was 1./ῌ and the annual speciﬁc runo#
was about 0,** mm in ,**/. Also the variations of ,+ outlet glaciers of the HPN from +3.././ to ,**./*/
were presented with their notable characteristics. The area loss due to recession in 0* years amounted
to ca. +** km,, of which close to -*ῌ was accounted by Glaciar San Quintin, the largest glacier of the HPN.
At Glaciar Perito Moreno, observations and measurements were carried out for ﬂow, strain gridand meteorological measurements, and calving activities. Flow velocity per day in December ,**.
ranged -.3/ to *./- m, with the average of +.00 m at the calving front. At the middle reach, the average
daily ﬂow velocity was +./ m, and the proﬁle survey revealed that the inner zone maintained thicker
conditions, but with no signiﬁcant trend of additional thickening. The annual mean temperaturenear the EL (ca. +-/* m) was +.*ῌ, while that at near the terminus was 0.-ῌ in ,**/.

+.

Introduction

The glaciological Research Project in Patagonia(GRPP) was initiated in +32-, as a joint project ofJapan and Chile (Nakajima, ed., +32/) and since then,the GRPP has been carried out with Chilean and/or
Argentinean partners (Nakajima, ed., +321; Naruse andAniya, +33,; Naruse and Aniya, +33/; Aniya and Naruse, ,**+a,b). This paper reports some of the major

96

Bulletin of Glaciological Researchresearch results of the latest project, GRPP*-ῌ*/.
The project title is “Holocene Environmental Changes
in Patagonia Iceﬁeld, South America”, with the main
objectives including:(+) to establish the Holocene glacial chronology of
the Hielo Patagónico Norte (HPN),(,) glaciological studies of Glaciar Exploradores,
HPN,(-) to continue monitoring of variation of the HPN
outlet glaciers,(.) to elucidate calving mechanism of Patagonian
glaciers, and(/) to establish paleomagnetic characteristics recorded in the Middle Miocene-Holocene igneous rocks
and sediments.
Of these, this paper reports the major results of
the objectives (+) to (.). The Patagonia Iceﬁeld lies
near the end of South America, between .0῍-*ῌ and/,῍-/ῌS along 1-῍-*ῌW, and it comprises the Hielo
Patagónico Norte (HPN, or Northern Patagonia Iceﬁeld, .,** km,) and the Hielo Patagónico Sur (HPS, orSouthern Patagonia Iceﬁeld, +-*** km,) (Fig. +). The
glacier area together, +1,,** km, makes the Patagonia
Iceﬁeld one of the largest in the world, and the largest
temperate icebody in the Southern Hemisphere,
where land mass is scarce. The Patagonia Iceﬁeld is
located in the westerly zone and characterized bylarge amounts of precipitation and melting/calving,making it highly susceptible to climate change. For
these reasons, it is very important to study glaciologi-

Fig. +.

Location of Hielos Patagonicos, South America.

cal aspects of the Patagonia Iceﬁeld, in order to understand the nature of global environmental changes atpresent as well as in the past.
GRPP*-ῌ*/ targeted mainly two glaciers, Glaciar
Exploradores of the HPN (Fig. ,) and Glaciar Perito
Moreno of the HPS (Fig. -). The reasons why wetook up Glaciar Exploradores are; (+) relatively easy
access for various measurements using instruments,(,) the glacier has been relatively stable over the last
0* years, and (-) it has a large terminal moraine infront of the glacier snout. Patagonian glaciers arenotorious for di$cult accessibility for scientiﬁc studies because of the weather and approach. Therefore,
the accessibility was one of the major factors to choose a glacier. The outlet glaciers of the HPN havebeen more or less receding during the last 0* years(Aniya, ,**+); yet the variation of Glaciar Exploradores has been relatively small. Holocene glacial chronology of the HPN has not been established, although Aniya and Naruse (+333) recognized two recent advances at Glaciar Soler on the east side of theiceﬁeld, at +-** BP and the Little Ice Age (LIA) around
AD+0/*. Recently, Glasser et al. (,**/) identiﬁed two

Fig. ,. Satellite image of Hielo Patagónico Norte (Landsat ETMῌ, March ++, ,**+) with names for outlet
glaciers, and the area of Glaciar Exploradores indicated with a rectangle.

Aniya et al.

97

ance. At Glaciar Perito Moreno, the large ice ﬂow
velocity has been observed and the inﬂuence of theglacier ﬂow on the glacier change is considered to begreat. It is presumed that glacier kinetics that o#sets
the mass imbalance has strong inﬂuences on glacierstability. In order to possibly understand or obtain aclue why the glacier is stable, we need a long-term
record of meteorological, glaciological and calving activity observations.

,.

Study Area

Glaciar Exploradores, HPN
The HPN is located around .1῍S and 1-῍-*ῌWwith an area of about .,** km, in +31. (Aniya, +322, seeFig. ,). It has the highest mountain in Patagonia,
Monte San Valentin (-3+* m) at the northeastern corner of the iceﬁeld. The iceﬁeld has ,2 outlet glaciers,of which ,+ major glaciers have been studied for theirvariations since +3.. to +333 (Aniya, ,**+). Glaciar
Exploradores is located at the northeast corner of theiceﬁeld on the north ﬂank of Monte San Valentin, withan area of about 3/ km,, a length of ,*.- km and an
AAR *.00 in +31. (Aniya, +322). The ablation area of
the glacier used to be formed by three glacier bodies,but one branch joining from the east has detached by
now due to recession. In front of the present glaciersnout, there is a big, continuous terminal moraine,with which prominent lateral moraines on both sides
are associated. If we can infer the age of this moraine, we may be able to establish a part of the Holocene glacial chronology of the HPN, because there aresimilar moraines at other glaciers such as Grosse,
Reicher, Gualas, Nef, Colonia to name but a few. Despite its relative stability when other glaciers of the
HPN have been rapidly retreating, no glaciologicalstudy has been carried out at Glaciar Exploradores
yet. Members who worked at this ﬁeld include;
Aniya, Aoki, Matsumoto, Barcaza, Sawagaki, Sato,and Iwasaki.
,.+

Fig. -. Hielo Patagónico Sur and Glaciar Perito Moreno.
(Landsat ETMῌmosait, March ++, ,**+)

glacial advances before the LIA advance, although
without assigning ages. For the HPS, three (Mercer,+310) or four (Aniya, +33/) Neoglaciations were identiﬁed. However, at the HPN, normally only two (Aniya
and Naruse, +333) or at some glaciers three (Glasser etal., ,**/) moraine systems are recognized between thepresent glacier snout and the Pleistocene moraines.
Glaciar Pertito Moreno of the HPS is one of themost studied glaciers in the Patagonia Iceﬁeld (e.g.
Skvarca and Naruse, +331); yet we do not know themechanism of its stability at least over the last 0*
years when other glaciers in Patagonia have been
retreating and thinning (e.g., Rignot et al., ,**-). The
characteristics of glaciers in Patagonia are large accumulation in upper zone and large ablation in lower
zone, which ice transport by glacier ﬂow makes bal-Glaciar Perito Moreno, HPS
Glaciar Perito Moreno is one of the most wellknown glaciers in Patagonia, because it is located in
the Glacier National Park of Argentina that has been
designated as the World Natural Heritage, attracting
many tourists from all over the world. It is locatedon the eastern side of the HPS at /-῍-*ῌS and 1-῍**ῌW,
with an area of ,/2 km,, a length of -* km and an AAR
of *.1- in +320 (Aniya et al., +330). The GRPPs havebeen studying this glacier since +33* and have accumulated a wealth of glaciological and meteorologicalinformation (e.g., Naruse and Aniya, +33,; Aniya et al.,+33,; AniyaandSkvarca,+33,; Naruseet al., +33,; Naruse
and Aniya, +33/; Naruse et al., +33/a; +33/b; Takeuchi
et al., +330; del Valle et al., +33/; Skvarca and Naruse,+331; Naruse et al., ,**+; Iizuka, et al., ,**.; Skvarca et
,. ,

98

Bulletin of Glaciological Researchal., ,**.). In addition, because of easy access, there
are few studies by others (e.g., Warren, +33.; Rott etal., +332; Michel and Rignot, +333). One of the mostwell-known and notable characteristics of Glaciar
Perito Moreno is the repeated advance with consequent damming up of lake “Brazo Rico-Sur” (Mercer,+30,; +302). The uniqueness of the glacier also includes its stability since the +3.*s despite the generaltrend of glacier recession in Patagonia (Aniya andSkvarca, +33,; Aniya et al., +331). The most recent
advance and damming up occurred in ,**-, which wasfor the ﬁrst time since +322. The ice-dam was eventually ruptured on March +-, ,**. (Chinni and Warren,,**.; Skvarca and Naruse, ,**0). Members who worked at this glacier include; Enomoto, Skvarca, Suzuki,
Isenko, Sala, Fukuda, Satow and Naruse.

-.

Studies at Glaciar Exploradores-.+ Geomorphology and recent glacial advances-.+.+ Moraine distributions and dating
At Glaciar Exploradores, a big, conspicuous terminal moraine has been clearly recognized (Harrison etal., ,**.) and it was assumed to be of the LIA from its
position. However, when we started the GRPP*- in,**-, we recognized another terminal moraine system
inside the big moraine (Aniya et al., ,**/). Then in
December ,**., we suspected another terminal moraine down below along Río Exploradores from theroad, which was subsequently conﬁrmed in the ﬁeld
in August ,**/.
Therefore, there are three moraine systems at
Glaciar Exploradores, which we denote here as TM+(oldest), TM, (main), and TM- (most recent). We collected dating materials from these moraines; two fromthe TM+, six from the TM,, and seven from the TM-,in order to establish the recent glacial chronology(Fig. .).
TM+ is located about - km down from the TM,, on
the right bank of Río Exploradores by the mountainslope. Its relief from the valley ﬂoor is more than ,/*m, with a length ca. +*** m and a width ca 3** m at thebase. It consists of a pile of gigantic boulders, whoselong axis ranges /ῌ+* m, and is densely covered withthick vegetation on well-developed soils. However,two dating materials (organic matters) yielded modern ages of ca. +** BP, which are obviously not indicative of the time period of the moraine formation.
TM, is the most prominent, conspicuous terminal
moraine here. At places, water seeps out from near
the base of the moraine, indicating that the moraine isstill ice-cored. The relief of the proximal side exceeds
2* m and it is limiting the entire glacier front in an arc,with spilling ways at the both end (one was dry by
now though). It used to have two spillways in the
middle, which became dry before +3./ and have become a wind gap since. We obtained six dates forFig. .. Sampling points for datings in front of Glaciar
Exploradores (Aerial photograph by SAF, Chile,
March ++, +331)

this moraine from wood samples: ,A, 3,/*ῌ/* BP; ,B,+3**ῌ/* BP; ,C, +.**ῌ.* BP; ,D, +*/*ῌ/. BP; ,E, 21*
ῌ/* BP, and ,F, 2,*ῌ0* BP. We also counted thenumber of tree rings of a cut tree by the road with adiameter of .* cm to be roughly ,** years (/ year/cm).
The largest diameter at breast height (DBH) aroundhere is /ῌ0* cm. With a simple linear extrapolation,
we obtain about -** years since the tree invasion.
The moraine system, TM-, is located between TM, and the current glacier snout, and can be divided
into two types, TM--+ and TM--,, according mainly tothe vegetation cover, size and morphology, among
others. TM--+ is located at the eastern edge by theoutlet stream, consisting of several ridges more or lessparallel to each other and the present snout. It haslarge Nothofagus whose DBH ranges to .*ῌ/* cm, justin front of the snout. The area is scattered withlimestone boulders, which cannot be found elsewhere
at Exploradores. TM-ῌ, is still mostly ice-cored withgenerally ﬂat topography; however, in places the surface has become hummocky partly due to di#erential
melting of the core ice. At many places, vegetation
has invaded and we can ﬁnd Nothofagus with the
DBH +/ῌ,* cm. Recent acceleration of core-ice melting is evident at many places, with trees falling and/or surface ponds enlarging. The following dates

Aniya et al.

were obtained for TM-: -A, ca. +*2 BP (plant); -B, ca.
+*3 BP (organic matter); -C, ca. ++/ BP (wood); -D, ca.
+,+ BP (wood); -E, ca. +,- BP (organic matter); -F, ca.
+-. BP (plant); -G, ca. +.1 BP (organic matter).
Ages of moraines and scenario of the recent glacial advances
From these datings, moraines’ topographic relations to each other, and tree ring analysis the following results and conclusions are reached.
(+) Invernada Moraine: the age could not be positively deﬁned as the ages obtained from the samples
are obviously too young to be of indicative of theformation age. However, from the date of the Main
Moraine, it could be of the Neoglaciation III (ca. +0**ῌ
+-** BP, Aniya, +33/).
(,) Main Moraine: from the six dates we obtained forthis moraine, the youngest, ca. 2,* BC (AD ++2*) seems
to delimit the moraine formation age. In addition,
tree ring analysis suggests that the trees invaded themoraine around ca. -** years ago. Therefore the moraine formation was probably sometime between the+,th and +1th centuries.
(-) Modern Moraines: Moraine -ῌ+ is probably formed during the early to mid-+3th century, while Moraine -ῌ, was formed after +3.././ from interpretation of the Trimetrogon aerial photographs.
Based on these dates, the following scenario seems
most probable. After forming the main moraine sometime between the +,th and +1th century, the glacierretreated. Then the glacier bodies that formed bothTM-ῌ+ and TM-ῌ, advanced at the same time aroundthe early to mid-+3th century. The glacier body thatformed TM-ῌ+ started retreating earlier than theother part (TM-ῌ,), and during the slow retreat theglacier formed a series of recessional moraines (midto late +3th century). Meanwhile, the large part of
the glacier that subsequently formed TM--, had beenstationary for a long time, being blocked by the large
main moraine. It was only ca. +3.*s when that part

99

started receding after a prolonged period of surface
lowering. Because of long stagnation (about +**years?), a mantle of thick debris has been developed,
which facilitated easy plant invasion under the mild
climate.

-.+.,Table +

Glacier ﬂow and its characteristics
In recent years, most of the outlet glaciers from theHielo Patagónico Norte have been receding quickly.
However, the terminus of Glaciar Exploradores has
been stable (Aniya, ,**+). He attributed its stability
to the debris cover in the snout area. During the
GRPP*-ῌ*/, we observed the ﬂow of Glaciar Exploradores with the following two purposes. The ﬁrst is tocheck whether or not the terminus is really stagnant,and the second is to consider the reason for the stability if the glacier is really found to be stable.
-.,

Measurement procedures
Due to its size and the di$culty to establish control points on either side of lateral moraines for theconventional triangulation survey to ﬁx the positionof a stake on the glacier surface, we used in stead thepost-processed di#erential GPS (D-GPS) method tomeasure the ﬂow velocity of the glacier. We madeD-GPS observations three times: December ,**-, December ,**. and August ,**/, each lasting for ,ῌweeks, during which several measurements were carried out. In December ,**-, the initial set-up of points
and measurements were undertaken by Aoki and
Sawagaki, while other observations in ,**. and ,**/
were done by Aoki alone. The instrument we used isa Topcon GP-SX+, which is a L+ single band receiver,and we used the WGS-2. for mapping coordinates.
In December ,**-, we established a point in thebase camp as the reference point for D-GPS, at which
we measured the position six times, each lasting foreight hours. Subsequently, the radius of the error
circle was found to be ,.* m and /.* m in the horizontal
and vertical component, respectively. Among six-.,.+

D-GPS measurements for the reference point (,**- and ,**. (M*2)).

100

Bulletin of Glaciological Researchmeasurements (Table +), we chose the one that wasnearest to the center of the horizontal error circle as
the reference coordinates for the subsequent D-GPS
measurements and processing of the points on theglacier. In December ,**., the reference point was
moved to M*2, because the base camp was moved, andthe same procedure was undertaken to obtain the newreference coordinates for the ,**. and ,**/ measurements.
In the / km stretch of the ablation area from theterminus, we set up six measuring points on big,
conspicuous erratics strewn on the glacier surface as
the permanent point, on each of which a bolt wasembedded for a GPS placement (Fig. /). Over the periods, some erratics tilted; however, the shift of the bolt
was not signiﬁcant, when considering the amount of
the movement. Point G+ was lost in ,**., probably
due to the boulder falling into a crevasse, and a point
G+B was newly established nearby as a substitute. In
addition, some temporary points were also set up on
the glacier ice by drilling a hole for a stake during theeach observation period. With the D-GPS measurements, we obtained the latitude, longitude and ellipse
height, of which the latitude and longitude were translated into the UTM coordinates using GIS (Geographic
Information Systems) to calculate the glacier ﬂow
with the Euclidean geometry. The vertical measurements were not converted to the orthographic heights, because the geoid height of the limited, small
area is safely assumed to be the same.
Results and discussion
The results of the measurements are shown in
Table ,. The annual ﬂow rates (Dec. ,**--Dec. ,**.)-.,.,

Table ,

Fig. /. Flow measurement points and their movements, along with the location of meteorologicaland hydrological stations.

Glacier ﬂow measurements at Glaciar Exploradores, HPN.

Aniya et al.

of points G,, G-, G., G/ and G0 range from .2 m to +-2
m. In addition, the ﬂow rate between the midsummer and the mid-winter (Dec. ,**.-Aug. ,**/) wereobtained for those ﬁve points and G+B.
Horizontal ﬂow
The glacier ﬂows were observed at all the measuring points, including even G+ and G+B that were seton the debris-covered snout area, only several tens ofmeters from a proglacial lake. These measurements
clearly indicate that the ice at the terminus area is not
stagnant; it is actively moving at a surprising rate.
The direction of the ice movement is o#set to the east
from the centerline of the glacier, probably because
the outlet stream is located on the eastern margin.
The relationship between the annual ﬂow velocity and the distance from the terminus indicates thatthe velocity decreases from the upper reach toward
the terminus almost linearly. Upon a close examination, however, there seems a slight gap between points
G. and G-. Points G-, G,, G+ and G+B are located on
the debris-covered ice, while points G., G/ and G0 are
located on the debris-free ice. The decreasing rate forpoints G.-G0 is higher than that for points G--G+, andtrend lines for each group are slightly o#set. Thisimplies that there is compression in the glacier ﬂow
between point G- and G.. Indeed the glacier surface
around G- shows a convex form. The glacial dynamics a#ected the surface morphology.
On ,, December ,**., a heavy rainfall was recorded (+,* mm/day) and the day after the ﬂow velocity increased by +,*ῌ+/*ῌ, suggesting that the basal
water of the glacier accelerated the glacier ﬂow.
From this observation, basal sliding and possibly basal deformation of till are signiﬁcant components of the
ﬂow at Glaciar Exploradores.
Vertical ﬂow
From December ,**- to December ,**., the change
in the surface elevation was not signiﬁcant at all the
points, although the high rate of surface melting wasobserved, indicating that the upwelling of ice compensated the loss of ice. From our measurements, theemergence velocity and the melting rate in the ablation area are found to be about the same, which isimportant for maintaining the stability of the terminus position.
In December ,**., the emergence velocities also
increased after the hard rainfall, suggesting that thehigher compression induced by the higher horizontal
ﬂow velocity enhanced the emergence velocity.
Concluding remarks
From the measurements of horizontal and vertical ﬂows in three periods, it was found out that Glaciar Exploradores is moving very actively, even at thedebris-covered terminus. This is why Glaciar Explo-.,.-

101

radores has been relatively stable when other glaciersof the HPN have been receding. However, from theﬁeld observation during ,**-ῌ,**/, it is apparent that
Glaciar Exploradores is now in the phase of slow,
gradual retreat, because the proglacial lakes and englacial ponds in the debris-covered terminus area are
expanding and the glacier surface has become increasingly hummocky.
Meteorology
In order to clarify the climatic condition on andaround Glaciar Exploradores and to estimate melt rateon the glacier, an automatic weather station (AWS)
was installed south of the ,**./*/ base camp toward
the terminus (+2, m a.s.l.), and it has been monitoring
meteorological elements such as air temperature, relative humidity, global radiation, wind speed, wind direction, atmospheric pressure and precipitation sincethen. Observations on spatial distributions of melt
rate and air temperature and of surface heat balancecharacteristics were also carried out on the ablation
area of the glacier in December ,**.. In addition,observations of air temperature and melt rate distribution were carried out in August and December ,**/.
The monthly mean air temperature and the monthly total precipitation at the AWS in ,**/ are shownin Fig. 0. At the glacier terminus, air temperature
was the highest in February and the lowest in August
in ,**/. The daily mean air temperature varied between 1 and +0῍ in summer and between ῌ+ and 1῍in winter. The annual mean temperature in ,**/ was
1./῍. There was only nine days with a negativevalue of the daily mean air temperature in ,**/, maybe due to low altitude and to the inﬂuence of maritime
climate condition. In contrast, maritime climate andthe cooling e#ect of glacier may have kept daily air
temperature lower than +/῍ in almost all days insummer.
It is widely known that the climatic feature of the
Paciﬁc coast in Patagonia is characterized by heavy
precipitation throughout the year. The sum of measured precipitation at the AWS was ,13. mm, with ,3days of record missing from late November; thus theactual precipitation during ,**/ could have been nearly -*** mm. At the moment we have no other data tocompare, with which to discuss whether or not thisvalue is close to the normal in the region. Precipitation intensity at the glacier terminus was usually
lower than / mm hῌ+, and thus the highest daily precipitation since December ,**. was +,* mm (,, December ,**.). On the other hand, the number of days
with precipitation in the year was very large, and it ishard to ﬁnd a clear pattern in the seasonal variation of
precipitation from our record. In four days during
the winter observation period in August ,**/, wetsnow fell and accumulated about - cm and +* cm thickon the terminus and the upper part of the ablation
-.-

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Bulletin of Glaciological Research

Fig. 0. The monthly mean air temperature, the total precipitation and the mean discharge at the terminus of
Glaciar Exploradores in ,**/. Because some data are missing for November, the precipitation total ofNovember is probably an underestimate.

area (VE2 in Fig. /), respectively. However, we supposethat the proportion of snowfall in the total precipitation would be small because air temperature usually
stayed higher than *῍ even in wintertime.
Wind blowing in the up-valley direction along
Río Exploradores was often observed at the AWS,
especially rainy and cloudy days. Thus, the frequencyof wind direction between southeast and southwestthat would indicate glacier wind was only ,*ῌ during
the observation period in December ,**., which is incontrast to at the terminus of Glaciar San Rafael
where glacier wind occurred 2*ῌ to 3*ῌ of the time
during the summer +32- (Ohata, +323).
The daily melt rate in the clean ice part of theablation area was 0* mm dῌ+ on average during theobservation period in December ,**., whereas that on
the ice covered by thin debris was 10 mm dῌ+. As aresult of the observation in December ,**/, we found
the relationship between the melt rate and the thickness of the debris cover which is quite similar to thosereported by many previous studies (e.g., Mattson etal., +33-) as follows: when the debris cover is thinnerthan around 1 cm, the melt rate tends to be higher
than clean ice, whereas if the debris cover exceeds thisthickness, the melt rate is retarded. Based on the
results of the observations of air temperature and themelt rate in December ,**., the degree-day factor in
the clean ice part of the ablation was calculated to be
1.+ mm῍ῌ+ dῌ+ on average.
Hydrology
We installed a hydrological station to measure
and record the water level of Río Deshielo (localname), the outlet stream from Glaciar Exploradores,-..

with the one-hour interval on a site very close to theglacier terminus in December ,**. (see Fig. / for location). The area of drainage basin is about ,*1 km,,thus the proportion of glacier-covered area is around0*ῌ. Hourly discharge was calculated from the recorded water level and the stage-discharge curve thatwas obtained from nine discharge measurements.
In Figure 0, the monthly mean discharge in ,**/ isshown. The daily mean discharge usually varied between .* and +** m- sῌ+ in summer and once in Marchexceeded ,** m- sῌ+ due to heavy rainfall. Even in
mid winter, discharge around ,* m- sῌ+ was continuously observed due to glacier ablation and rainfall.
The annual speciﬁc runo# from the drainage basin in,**/ was about 0,** mm. This value is consistent
with the estimates of the annual speciﬁc runo# (/1**ῌ
01** mm) obtained from the water balance computation within the river basins around the HPN by Escobar et al. (+33,). One of the interesting features foundin hydrological regime of Río Deshielo is that thediurnal discharge variation appeared less clear thanmany other proglacial streams in the world throughout the year, while discharge usually showed a remarkable increase after a severe rainstorm. Thismay have resulted from frequent rainfalls, that is,
contribution of water from the non-glacierized areathat occupies about .*ῌ of the whole drainage basin.
However, we have no clear explanation on this featureyet.
Due to high sediment supply from the glacier,stream water always contained suspended sediment
during the observation period (in contrast, suspended
sediment concentration in Río Norte and its tributaries in the area upstream from the terminus of Glaciar

Aniya et al.

Exploradores during winter was visually observed tobe very much low). Suspended sediment concentration measured at the hydrological station varied between *.+ and *.1 g Lῌ+ during the period.

..

Glacier variations of the HPNDuring the GRPP*-ῌ*/, aerial surveys were carried out in December ,**-, July ,**., December ,**.
and August ,**/. The aerial survey of July ,**. wasthe ﬁrst such attempt in Patagonia in winter andrevealed many interesting and important features,
which have been heather to date unknown to thescientiﬁc community. For example, despite the middle of winter, ablation areas of many glaciers, particularly those on the west side of the iceﬁeld were free ofsnow, with bare ice and crevasse openings. During
this survey, those on the east side were covered withsnow, indicating together with winter Landsat images(e.g., July +,, +333; July ,/, ,**.) that during wintersnow falls much more on the east side than on thewest side of the iceﬁeld. Subsequent ﬁeld campaign
in July-August ,**/, including both ground investigation and two aerial surveys in July and August, revealed that snow on the ablation area melt away
quickly, for example +*ῌ,* cm of snow in a day or two
with the sun, indicating warm temperature.
Among those ﬁve aerial surveys, data of Decembers ,**- and ,**. were used to update the glaciervariation to ,**./,**/ from the previous work (Aniya,,**+). In this updating work, aerial photographs of

ca. +: 1*,*** taken in +331/32 were available (see fordetail Aniya, ,**1), and the previous snout positions ofsome glaciers were modiﬁed and the varied distanceand area were measured again to modify the statistics.
Figure 1 shows the variation of ,+ outlet glaciers from
+3.././ to ,**./*/.
During the last 0* years, the general trend has
been recession with a wide variety of retreating rates,
thereby losing an area of ca. +** km,. There are a few
notable characteristics in the variation. First of all,the area loss of Glaciar San Quintin, the largest glacierin the HPN, is outstanding with ca. ,3 km,, accounting
nearly -*ῌ of the total area loss. The neighboring
glacier, Glaciar San Rafael, retreated almost as fast as
San Quintin until ca. +33*; however, the variation during the +33*s and the ,***s has been quite di#erent
from San Quintin. While San Rafael has become
more or less stable with repeated stagnation/advance/retreat, San Quintin has continued to recede
fast. It seems imminent at San Quintin that snout
disintegration will soon occur at any time. The terminus oscillation of San Rafael after +33* seems tohave been strongly controlled by the fjord topography (primarily width, with some inﬂuence of depth aswell), because the oscillation has occurred where thewidth of fjord changes. Glaciar León, on the other
hand, varied very little over the same period, while
the neighboring glaciers, Glaciares Soler (to the south)and Fiero (to the north) have been gradually retreating.
Contrasting behaviors of two neighboring debriscovered glaciers, Grosse and Exploradores are alsointeresting to note. They both are located on thenorth side of Monte San Valentin (-3+* m), the highest
mountain in Patagonia, and hence are not directly
connected with the iceﬁeld. Glaciar Grosse started
forming a proglacial lake during the +32*s and sincethen the proglacial lake has been steadily growing.
Glaciar Exploradores, in contrast, has remained moreor less stagnant during the same period, because of
the strong emergency ﬂow near the snout. The di#erence in winter precipitation due to their relative locations in the iceﬁeld (Grosse-northwest side; Exploradores-northeast side, of Monte San Valentin) may account for these recent contrasting behaviors.
It would be interesting to compare the summer
and winter photographs of the same year to see whether or not there is a seasonal ﬂuctuation.

/.

Studies at Glaciar Perito Moreno

Observation sites
Observations of ice velocity at the terminus, glacier surface height and ﬂow in the middle reach werecarried out in November and December ,**., and in
December ,**/. The observation points are shown in
Fig. 2.
/.+

Fig. 1. Area changes of ,+ outlet glaciers of the HPNfrom +3.././ to ,**./*/. One tick on the rightordinate indicates + km, change (down-decrease;
up-increase).

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Bulletin of Glaciological Research

At the glacier terminus, ice movements were measured by tracking ice pinnacles at the calving front,
and short-term change of the glacier ﬂow was investigated. The water level of the glacier lake and glaciercalving activities were monitored by a water level
gauge. Di#erential GPS (D-GPS) observations wererepeated in the middle reach. The air temperature
was recorded on the surrounding slope of Glaciar
Perito Moreno and on the north slope of Co. (Mt.)
Cervantes (,-2* m).
Glacier ﬂow velocity at the terminus
At the glacier terminus, the ﬂow velocity of theglacier was measured by triangulation from the opposite shores of a bay in Lago (Lake) Brazo Rico, thesame as Naruse et al. (,**+). In November and December ,**., more than ten targets were observed fora one-month period, with the maximum ice velocity of-.3/ m dῌ+, the minimum of *./- m dῌ+, and the average/.,Fig. 2. Observation points for glacier ﬂow and surface
elevations at Glaciar Perito Moreno.

Fig. 3.

of +.00 m dῌ+. During the two-week observation in
December ,**/, the maximum velocity was -./. m dῌ+,the minimum *./+ m dῌ+ and the average +.-. m dῌ+.
The average of the two years yields a large ice velocity of +./ m dῌ+.
The daily ﬂow velocity was investigated for onemonth long in November and December ,**. (Fig. 3).
The increase in ﬂow velocity was observed on December 0. Since this increase was observed at several
points, it was not caused by collapse of a local ice
block, and some conditions for increasing ice velocity
must have existed in this zone. Precipitation was
suspected, but unfortunately it was not recorded. Because November and December ,**. had much rain
for this area, the precipitation may have inﬂuenced
the frequency of calving and large-scale collapses.
Calving frequency
With the same method as Iizuka et al. (,**.), awater gauge was installed at the opposite side of acalving front, which recorded at a ,-second interval,
and large waves due to collapse of ice blocks from thecalving front were observed. The waves by calving
lasted over +* seconds with the amplitude over +* cm;
thus they can be easily distinguished from waves
caused by wind. The calving frequencies in November and December ,**. are shown in Figure +*. Since
the gauge was set on a single site and recurring waves
were integrated when the amplitude exceeded +* cm,
this data indicate relative values of the scale andfrequencies of calving. An amplitude exceeding ,*cm indicates the occurrence of a big calving.
These data show that calving activities increasedon particular dates, December - and .. Since thefrequency of smaller (i.e., +* cm) amplitude increased,
there could have been a large number of small calving. The increase in the glacier ﬂow velocity wasobserved during these two days, which may have/.-

Daily variation of glacier front velocity at Glaciar Perito Moreno, in November and December ,**..

Aniya et al.

Fig. +*. Frequency of calving from Glaciar Perito
Moreno to Lago Brazo Rico, in November andDecember ,**..

elevation has been monitored since +33* (Skvarca etal., ,**.) and thickening was recognized by the observation in austral summer of ,**,/*-. While the innersites showed the continuous thickening trend in ,**-,
the lateral zone did not. From the observations in,**. and ,**/, the thickening trend was not observed
although the elevation remained at a high level.
Since this area is in the ablation zone, surface
elevation change can ﬂuctuate due to changes in melting, ice ﬂow and/or dynamic conditions of the glacier.
We set ﬁve measuring points for D-GPS survey andmeasured deformation of three strain grids on the ice
surface (Fig. ++). By repeating the measurements ofdisplacements of these points, we can calculate ice
deformations for divergence/convergence and vertical ice motions, thereby the emergence velocity can be
estimated for grids, T+, T, and T-. The ice thickness
data are available from the seismic-wave observationin +33/ (Stuefer, +333) and was used for this calculation. The D-GPS survey was done in December ,**.,and March, July and December ,**/. The preliminary result from the ﬁrst half of the year (,**/) shows
an ice velocity of +./ m dῌ+ on average. This is almost
the same as the previous measurement (Naruse et al.,+33/b).
The grid T+, which is located near the lateralzone, showed a negative emergence velocity (sink ordivergence), while grids T, and T-a that are located in
the inner zone showed a positive emergence velocity(rise or convergence). There are strong variations in
the vertical motion in place and time.
This uplifting area is the same as the area of alarge inter-annual variation in the surface elevation,
which has been monitored since +33*. The dynamic
behavior will be an important factor for explaining
the unique variation of Glaciar Perito Moreno. The
data are still being accumulated in ,**0 to investigate
the e#ects of ice advection and in-situ dynamics.
Temperature record
The winter observation reported that the lower
part of Glaciar Perito Moreno showed ablation even in
winter. On the other hand, in the upper part, snowfall was expected even in summer. The air temperature record around the altitude of the equilibrium line
(ca. ++/* m) is useful information with which to infer
the occurrence of ablation. The air temperature record was obtained by an AWS that was set-up on thenorth slope of Co. Cervantes (see Fig. 2). The annual
mean temperature for ,**.ῌ,**/ was ca. +.*῍. The
temperature frequently became below zero; thus there
were many occasions of snowing in this area throughout a year. On the other hand, the annual mean
temperature at the glacier terminus area was 0.-῍,
and the winter temperature was positive in the monthly mean. Since the seasonal variations at thesestations were small, the di#erence of /῍ between/./

Fig. ++. Observation of glacier deformation by D-GPS
set at the middle reach of Glaciar Perito Moreno.
Five measuring points and three strain grids were
set in December ,**..

been related to the increased calving activities.
/..

Middle reach proﬁleIn the middle reach shown in Figure 2, the surface

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Bulletin of Glaciological Researchthese two stations results in contrast in the ablation
and accumulation patterns on this glacier; that is, yearround accumulation in the upper zone possible, while
year-around ablation in the lower zone possible. A
strong glacier ﬂow would balance the ice masses between the upper accumulation zone and the lower
ablation zone including calving area.
Discussion on lake water level change, calving, andablation
Lago Brazo Rico is located to the south of Glaciar
Perito Moreno and connected with Lago Brazo Sur.
Their areas together are ++1.3 km, (Skvarca and Naruse, ,**0). The water level of the lake is closely
related to a glacial change. Advancing glacier tongue becomes an ice dam when reaching the opposite
bank, thereby causing the lake water level to rise,making the glacier front and ice dam instable.
There has been recurring formation and collapseof ice dam and water level changes at an interval ofseveral years to ten years (Skvarca and Naruse, ,**0).
In a short-time scale, there is a seasonal cycle of thewater level, an increase in summer and a decrease in
winter, which is related to daily calving and melting
variations. The water level gauge is a good indicator
for these phenomena.
The variation in the water level after that event
indicates that it rose quickly between December ,**.
and February ,**/ with a speed of +.- cm d῍+ and a
total of *.1 m in // days (Fig. +,). After reaching apeak on February +., ,**/, it started decreasing toward winter with some irregularities around May.
After hitting the minimum on July ,-, the lake surface
started to rebound quickly. A comparison of thetemperature record and the water level change indicates a seasonal change in unison with the winterminimum and a short variation of ,ῌ- months.
The water level record indicates that fall of thewater level stopped in July, and after August, continuous water level rise started. The glacier front
becomes unstable with a water level rise, and thencalving can be enhanced. There is an interaction of
glacier and lake changes.
/.0

Fig. +,.

Water level change of Lago Brazo Rico.

Toward understanding the glacier change in Patagonia, elucidation of inﬂuences of melt water andglacier dynamics is fundamental. A large amount ofmelt water ﬂows out through the inside of a glacierand from the bottom, which is expected to greatly
a#ect glacier dynamics and state. The amount ofsnow accumulation in the upper iceﬁeld and its transport downward by glacier ﬂow, the amount of melt
water, and ice dynamics are still unknown parameters
for Patagonian glaciers.

Acknowledgments
This study was supported by a grant in aid for
Scientiﬁc Research of Japan Society for Promotion of
Research (No.+/,/-**+, Principal investigator, M.
Aniya). We thank Compaña Hielo y Aventura, Prefectura Naval Argentina, Parque National Los Glaciares for ﬁeld campaign at Glaciar Perito Moreno, and
H. Rott, University of Innsbruck, Austria, for collaboration of the meteorological data at Glaciar Perito
Moreno.

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