83
Changes in Surface Morphology and
Glacial Lake Development of Chamlang South Glacier in
the Eastern Nepal Himalaya since 1964
Takanobu SAWAGAKI1*, Damodar LAMSAL2, Alton C BYERS3 and Teiji WATANABE1
1
Faculty of Environmental Earth Science, Hokkaido University
N10, W5, Sapporo, 060-0810, Japan
2
Graduate School of Environmental Science, Hokkaido University
N10, W5, Sapporo, 060-0810, Japan
3
The Mountain Institute, 100 Campus Drive, 108 LA Elkins, WV 26241, USA
*e-mail: [email protected]
Abstract
We carried out multi-date morphological mappings to document the development of the glacial lake
‘Chamlang South Tsho’ in the eastern Nepal Himalaya over four decades. High-resolution Corona KH-4A and
Advanced Land Observing Satellite (ALOS) PRISM stereo-data taken in 1964 and 2006 were processed in
the Leica Photogrammetric Suite (LPS) to generate digital terrain models (DTMs). The DTMs produced
topographic maps representing elevations and morphology of the glacier surface with a maximum error of
+/- 10 m. A bathymetric map was also produced based on sonar sounding data obtained in November 2009.
Extensive surface lowering was found to have occurred since 1964, as high as 156.9 m in the upper glacier
area. The average lowering of the glacier for the entire 42-year period from 1964 to 2006 is 37.5 m, with the
average surface-lowering rate calculated at 0.9 m/year. The average surface lowering for the 45 years from the
glacier surface in 1964 to the lake bottom in 2009 was 99.5 m at a rate of 2.2 m/year. The minimum and
maximum surface lowering during that period were 12 m and 153.8 m, respectively. The area surrounding the
largest supraglacial pond in 1964 exhibited a low surface gradient, and there had already been a large degree
of ice melting that favoured further lake expansion. The larger lowering rate at the lake area supports the
previously presented idea that ice calving into the pond triggered the larger and faster up-glacial lake
expansion.
Key words: ALOS PRISM, Chamlang South Glacier, Corona, digital terrain model, glacial lakes,
Nepal Himalaya, photogrammetry, satellite images, surface morphology, topographic map
1. Introduction
Glaciers in the Hindu Kush-Himalaya have been
receding and melting since the end of the Little Ice Age
in 1850 (Fujita et al., 2001; Bolch et al., 2008a, 2011;
Shrestha & Aryal, 2010; Fujita & Nuimura, 2011). One
of the consequences has been the formation and expansion of glacial lakes, particularly during the last half
century, as a result of glacial retreat that is most likely in
response to contemporary global warming and regional
warming trends (Yamada & Sharma, 1993; Mool et al.,
2001; Bajracharya et al., 2007; Watanabe et al., 2009).
As a result, the potential for glacial lake outburst floods
(GLOFs) is increasing throughout the Hindu KushHimalaya (e.g., Watanabe et al., 1994).
Supraglacial ponds and lakes are likely to form on the
surface of debris-covered glaciers when conditions are
Global Environmental Research
16/2012: 83-94
printed in Japan
favorable (Reynolds, 2000; Quincey et al., 2007), i.e.,
exhibiting a glacier surface gradient of less than 2°, low
ice velocity, and/or complete stagnation. Sakai and Fujita
(2010) discussed the importance of the glacial surface
lowering since the Little Ice Age. Glacier recession and
associated phenomena have multiple impacts and significances, all of which need to be considered in an integrated manner (Haeberli et al., 2007; Hegglin & Huggel,
2008). Most importantly, an understanding of the recession of debris-covered glaciers is absolutely necessary in
terms of hazards assessment, primarily because the
glacial lakes that form on them sometimes produce
devastating GLOFs (Clague & Evans, 2000; Richardson
& Reynolds, 2000a, 2000b; Ives et al., 2010), which are
often several times larger than normal climatic floods
(Cenderelli & Wohl, 2001). GLOFs can cause widespread damage and loss of life, property, infrastructure,
©2012 AIRIES
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T. SAWAGAKI et al.
and the geomorphic environment (Ives, 1986; Vuichard
& Zimmermann, 1987; Cenderelli & Wohl, 2003;
Narama et al., 2010). A thorough understanding of
glacial recession is also critical to the estimation of the
glacier mass balance for water resource management
within a given region (Bolch et al., 2008b; Immerzeel
et al., 2010).
Mapping of glacier area change can be carried out
with non-stereo orthorectified imagery; however, multidate, stereo-capable data are required in order to calculate
volumetric changes of glaciers, especially for the debriscovered type. Multi-date stereo-images with long-period
time differences as well as high spatial resolution are
needed to produce accurate and detailed 3D topographic
or terrain maps, that in turn can expand our understanding of the morphological changes of a glacier’s
surface. Photographic products from the Corona program
(~1960 to 1972) are the oldest remote sensing stereo
images publicly available with a wide geographic
coverage and high spatial resolution (~1.8 to 7.6 m).
Likewise, the Advanced Land Observing Satellite
(ALOS) PRISM, is a relatively new remote sensing
satellite program (launched in 2006) that has stereo
capability capable of generating digital terrain models
(DTMs) and 3D maps, and which also offers high spatial
resolution stereo-data (2.5 m). Several studies have
investigated volumetric changes in glaciers in the
Himalaya using either Corona or ALOS data (e.g., Bolch
et al., 2008a; Lamsal et al., 2011). Corona data have a
complex geometry, lack metadata (ephemeris) pertaining
to image acquisition, and require highly sophisticated
image- processing software to extract 3D information.
Despite this, Corona data provide an invaluable source
for investigation in various fields such as glaciology and
archaeology. Detailed information on Corona and ALOS
PRISM data and their processing is described well by
Lamsal et al. (2011).
During the past several decades in the Mt. Everest and
Makalu-Barun national parks of Nepal, 24 new glacial
lakes have formed and 34 major lakes are reported to
have grown substantially as a result of climate change
and regional warming trends (Bajracharya et al., 2007).
Recent analyses of comparative satellite imagery have
suggested that at least twelve of the new or growing lakes
within the Dudh Kosi watershed, nine of which are
located in the remote Hongu valley of Makalu-Barun
National Park, are ‘potentially dangerous’ based on their
rapid growth over the past several decades (Bajracharya
et al., 2007; Bajracharya & Mool, 2009). However,
despite the large amount of national and international
media attention recently generated by these new and/or
growing lakes in the Hongu valley, relatively little was
known about them in 2009 because of their extreme
remoteness and difficult access.
In response, we carried out the first scientific field
investigation of these glacial lakes in October-November
of 2009 (Fig. 1). At the time, a glacial lake situated at the
southwestern foot of Mt. Chamlang was considered to be
Fig. 1 Location of the Chamlang South Tsho in the Hongu valley, eastern Nepal
Himalaya. CST: Chamlang South Tsho, CNT: Chamlang North Tsho.
Changes in Surface Morphology and Glacial Lake Development of Chamlang South Glacier
among the most dangerous of the nine ‘potentially
dangerous’ lakes within the valley (Mool et al., 2001;
Bajrachayra et al., 2007; ICIMOD, 2011), prompting the
research team to focus its activities on the Chamlang
South Glacier while conducting preliminary analyses of
the other eight lakes. Respecting its positional relationship with the peak, we call this lake ‘Chamlang South
Tsho’ although it has been referred to by various other
names. The aim of our study was to examine changes in
surface morphology of the Chamlang glacier and the lake
between 1964 and 2006.
2. Study Area
Chamlang South Tsho (longitude: 86˚57’33”E, latitude: 27˚45’24”N), has been called different names by
different researchers, e.g., Chamlang Tsho in the 1:50000
Schneider map, Chamlang Pokhari by Byers et al. (2012),
and most commonly West Chamlang in the 1:50000 topographic map by the Survey Department of Nepal and in
Mool et al. (2001) and Bajracharya et al. (2007), which
also provided an identification number of kdu_gl 466.
Mt. Chamlang has two glacial lakes on the westward side
of the peak: one in the northwest, with no local name but
an identification number of kdu_gl 464 (Bajracharya
et al., 2007), and the other in the southwest region of the
peak (Fig. 1). To avoid confusion, we propose the use of
the name of Chamlang South Tsho for the lake located in
the southwest region.
85
Chamlang South Tsho has developed rapidly between
1964 and 2000 on the debris-covered Chamlang South
Glacier (Fig. 2). The altitude of the lake surface is
4,940 m.
3. Data and Methods
3.1 Image processing
Two sets of stereo-data (ALOS PRISM and Corona)
with a time span of over four decades were used. ALOS
PRISM data (acquired on 4 December 2006; Path: 140,
Row: 41, spatial resolution: 2.5 m) with processing level
1B1 (radiometrically calibrated data) plus Rational
Polynomial Coefficient (RPC) data files were obtained
from the Remote Sensing Technology Center of Japan
(RESTEC). ALOS PRISM acquires data in triple mode F,
N, and B (forward, nadir, and backward). With these data,
<10 m geometric accuracy is achievable (Tadono et al.,
2009).
Images acquired from Corona camera systems KH-1,
KH-2, KH-3, KH-4, KH-4A, and KH-4B were declassified in 1995 and became available in a digital format in
2003 (McDonald, 1995; Galiatsatos et al., 2008). The
early systems of KH-1, KH-2, and KH-3 were equipped
with a single panoramic camera, while the latter systems
of KH-4, KH-4A, and KH-4B were equipped with both
forward- and backward-looking cameras. The images
taken by the KH-4, KH-4A, and KH-4B camera systems,
which have a stereo capability, a higher spatial resolution
Fig. 2 Landform features and surrounding geomorphic environments of the Chamlang South Glacier.
Corona KH-4A image depicting the supraglacial ponds and glacier surface in 1964 (a) and
IKONOS image acquired in 2000 (b) showing the morphological change of a large lake (Chamlang
South Tsho) from 1964 to 2000. C1–C5: Abandoned channels, P: Current largest pond.
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T. SAWAGAKI et al.
(3.00-7.60, 2.70-7.60 and 1.8-7.60 m, respectively) and
wide area coverage offer the oldest available stereo data.
Corona panoramic filmstrips contain inherent geometric
distortions, which need to be rectified to extract reliable
information from its images (Slama, 1980; Altmaier &
Kany, 2002). Typical geometric distortions of a Corona
image gradually increase from the centre to the extreme
edges of an image along the track (Slama, 1980; Altmaier
& Kany, 2002; Lamsal et al., 2011). The processing of
Corona stereo images for DTM generation has been well
described by Altmaier and Kany (2002), Bolch et al.
(2008a) and Lamsal et al. (2011). Corona KH-4A stereo-pair images (acquired on 26 November 1964, entity
ID: DS1014-2118) of the study site were obtained from
the USGS in a digital format scanned at 3,600 dpi
(7 microns).
Stereo images were processed with the aid of the
Leica Photogrammetric Suite (LPS). DTMs and topographic maps were produced after rigorous editing of the
triangulated irregular network (TIN) model. Stereo
MirrorTM/3D Monitor and Leica 3D TopoMouse greatly
facilitated and enhanced the tasks of image processing
such as ground control point (GCP) collection and terrain
editing. A fully editable Leica Terrain Format (LTF) and
a TIN (vector DTM) model was created for each dataset,
so that the editing of inherent errors took place with
automatically generated DTM to produce accurate 3D
terrain maps.
ALOS PRISM images (F, N and B) with RPC file and
three GCPs (collected from a map of the Everest area
compiled by the National Geographic Society in 1988)
were employed to triangulate (RMSE ~0.40 pixel) stereo
images to create a stereo model and were used for DTM
generation. A stereo model was generated for the entire
area covered by the scenes; however, only a DTM of the
study area was created. The vector DTM was edited upon
viewing the stereo model as a base. Extensive editing was
carried out upon viewing the stereo model until satisfactory terrain representation with mass points was achieved.
Thick or thin distribution of mass points that did not truly
represent ridges, ponds, and depressions were also edited
to ensure that enough had been accurately represented.
Densification and thinning of mass points were mainly
carried out during terrain editing, so that the produced
DTM would duly represent the actual terrain surface.
After rigorous terrain editing a promising DTM was
produced (Fig. 3); image processing tasks, including
DTM editing, are well described by Lamsal et al. (2011).
To correct the geometric distortions of the Corona
images, a non-metric camera model was selected in the
LPS platform. This requires only the focal length and
pixel size of the scanned image, and the flying height of
the camera platform as input for interior orientation
parameters (IOPs) (Altmaier & Kany, 2002; Casana &
Cothren, 2008). Acquiring reliable GCPs from identical
locations is one of the most crucial tasks in
Fig. 3 Location of the ground control points (GCPs) denoted by white triangles (a). The
red box shows the area shown in (b). Figure 3b shows a representation of
landform by mass points, triangles and contour lines in vector DTM (LTF).
Changes in Surface Morphology and Glacial Lake Development of Chamlang South Glacier
photogrammetric operations for producing quality DTMs
and topographical maps. The GCPs for the Corona
images (Fig. 3) were taken from corrected ALOS stereo
models, with meticulous care given to their accuracy.
Afterwards, approximately 100 tie-points were automatically generated with an image matching technique
for stereo data based on the provided IOPs and exterior
orientation parameters (EOPs). All tie points were
automatically placed at the correct locations on both
images (forward and backward). Aerial triangulation was
then performed (RMSE ~1.25 pixel) to produce a vector
DTM. Later, substantial DTM editing was carried out to
obtain a representative terrain surface as explained
above.
3.2 Evaluating the accuracy of the produced DTMs
and topographic maps
The pond/lake boundary of Chamlang South Tsho
was delineated from the surrounding moraines and
glacier while viewing the DTM superimposed over the
stereo model of the ALOS PRISM data. The surroundings are higher than the lake surface, and the texture of
the lake is also different. The flat lake surface is easily
identifiable on the stereo model. Uncertainty in delineating the precise lake boundary over the stereo model is
believed to be very small, i.e., less than one meter.
The accuracy of the produced DTMs and topographic
maps of the Chamlang South Glacier was also assessed
by differentiating the 2006 ALOS DTM from the 1964
Corona DTM in the unaltered area outside the lateral and
terminal moraine boundary. As shown in Fig. 2, the
Chamlang South Glacier is surrounded by lateral and
terminal moraines. The glacier surface within the lateral
and terminal moraines is subject to surface lowering
because of glacier melt. It is assumed that the surface
beyond the lateral moraines has remained unchanged.
This unchanged surface (buffer of ~0.55 km2) beyond the
lateral/terminal moraines is used for assessing the consistency among the DTMs and the topographic maps.
Figure 4a is a portion of the elevation change map
beyond the lateral moraines (unchanged ground) of the
Chamlang South Glacier. The glacier surface area within
the lateral moraines was masked for the calculation. The
difference between the Corona and ALOS DTM ranges
from 11 to –13 m (Fig. 4a). To quantify this DTM error
more precisely, a histogram of DTM differences was
prepared (Fig. 4b). The calculations were carried out on a
3 × 3 m grid, and the total pixel count was 59,001. Subsequently, the pixel count for each class was converted to
an error percentage. The classes with the most dominant
DTM difference were –1-1 m (26%) and 1-3 m (26%),
while the classes with negligible influential difference
were –13 - (–11) m (0.1%), –11 - (–9) m (0.2%), –9 - (–7) m
(0.4%), 7 - 9 m (1%), and 9 - 11 m (0.2%). The range of
DEM differences from –5 to 5 m accounts for 90.9% and
the range from –1 to 3 m comprises 52.0%. As a result, it
is concluded that a maximum relative DEM error of 10 m
may exist in the generated DTMs and the topographic
maps of the Chamlang South Glacier.
87
The use of Corona data to generate a DTM has been
extremely limited in the scientific literature. The few
studies that do exist include Altmaier and Kany (2002)
with Corona KH-4B; Bolch et al. (2008a, 2011) with
Corona (KH-4) and ASTER; and Lamsal et al. (2011)
with Corona KH-4A and ALOS PRISM. We employed a
combination of Corona KH-4A (spatial resolution,
2.7-7.6 m) and ALOS PRISM (spatial resolution, 2.5 m)
data as used by Lamsal et al. (2011) to generate DTMs
and topographic maps. Three-dimensional topographic
mappings with Corona KH-4A and ALOS PRISM stereo
imageries can represent glacial surfaces, including
micro-landforms, such as supraglacial ponds, depressions, moraine ridges, and ice cliffs satisfactorily well
with a high accuracy. However, the DTMs produced with
automatic procedures were largely unsatisfactory, which
led to extensive DTM editing to remove unnecessarily
thick mass points or to add mass points where their
distribution was thin. Despite careful editing of DTMs,
there may still be small errors (a maximum of +/– 10 m).
However, representation of the terrain of the glacier surface was entirely satisfactory for the present purpose.
a)
b)
Fig. 4 Portion of the elevation change map beyond the
lateral and terminal moraines of the Chamlang South
Glacier, showing unchanged areas (a), and a
histogram of DEM differences (b).
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T. SAWAGAKI et al.
3.3 Bathymetric survey
Many researchers have examined the areal expansion
rates of glacial lakes in the Himalaya by using photographs, maps and satellite images (Watanabe et al., 1994;
Yamada, 1998; Ageta et al., 2000; Haeberli et al., 2001;
Yabuki, 2003; Byers, 2007; Sakai et al., 2007;
Racoviteanu et al., 2008, 2009; Byers et al., 2012).
However, few studies have investigated bathymetric
changes in the supraglacial or proglacial lakes and ponds
of concern (cf. Benn et al., 2001; Fujita et al., 2009),
partly because it is extremely difficult to gain access to
most of the high altitude glacier areas in the Himalayan
mountains. Recurrent measurements have also been
restricted or are completely absent. Still, it is important to
measure the water depth of glacial lakes in order to have
a better understanding of the expansion process
mechanisms involved (e.g., Röhl, 2008; Sakai et al.,
2009).
We carried out geomorphic observations and a bathymetric survey at and around Chamlang South Tsho
between 26 and 29 October 2009, at the end of the
ice-melting period. The lake water depth was confirmed
continuously using sonar sounding from a boat. Fishing
sonar (Fish Elite 500C) was utilized for sounding the
depth. Depth measurement points were simultaneously
recorded by GPS.
which have already been abandoned (Fig. 2a). These
channels suggest that the former melt-water drainage
over- spilled when the glacier surface was much higher
than today. The magnitude of the overspill was determined not to be large, based on the small size of the
depositional landforms on the terminal moraines. The
largest channel located to the northwest of the terminal
moraine currently has surface water (a small river), the
uppermost of which is subsurface flow. The water of this
small river is most likely derived from the pond shown as
P in Fig. 2b.
Morphologies shown in Fig. 5 were converted to
DEMs (Fig. 7) for the purpose of raster-based calculations to quantify glacial morphology and its change by
producing elevation change maps and surface profiles.
Here, we use the term ‘lowering’ in a descriptive manner,
without suggesting specific processes, because this is
more favorable to the description of morphological
changes that occurred between 1964 and 2006.
4. Results and Discussion
Figure 5 shows the surface morphologies around the
Chamlang South Glacier with topographic maps in 1964
and 2006 at contour intervals of 2 m (faint lines), 10 m
(lighter bold lines), and 20 m (bold lines), mapped by
Corona KH-9 and ALOS PRISM stereo images, respectively. As can be seen when comparing the two images,
noticeable glacial surface morphology change occurred
during the 42-year period from 1964 to 2006.
Corona KH-4A image shows a few supraglacial
ponds in 1964 (Fig. 2a). These ponds were most probably
very small in 1962 when a climbing expedition team
from Hokkaido University scaled the summit of Mt.
Chamlang. The largest pond was located at an altitude of
4,952 m, and the glacial surface upward from the pond
had a relatively steep gradient in 1964 (Fig. 5a). The
steep section of the glacier had completely melted out by
2006 resulting in the formation of a large lake,
‘Chamlang South Tsho’, that had a lake water surface
altitude of 4,940 m in 2006 (Fig. 5b). This suggests that
some 12 m of lake surface lowering had occurred during
the period between 1964 and 2006. As shown in the
bathymetric map (Fig. 6), the current lake is approximately 550 m wide (north-south) and about 1,650 m long
(east-west), with the bathymetric survey suggesting that
the maximum water depth is 87 m. The current lake area,
8.7 × 107 m2, is roughly six times larger than that shown
on the Schneider map (surveyed between 1955 and 1974).
The total water volume is estimated to be 35.6 × 106 m3.
The terminal moraine of the Chamlang South Glacier
has six dissected channels (Figs. 2a and 2b), five of
Fig. 5 Topographic maps of the Chamlang South Glacier in
1964 (a) and 2006 (b). Contour intervals: 2 m (faint
lines), 10 m (lighter bold lines), and 20 m (bold lines).
The red lines show the lateral and terminal moraines.
Fig. 6 Bathymetric DEM of the lake in 2009.
Changes in Surface Morphology and Glacial Lake Development of Chamlang South Glacier
In Fig. 7, the surface morphologies for both years are
represented in eleven classes (ranging from 4,710 5,150 m at 40-m class intervals) with the same 11 ranges
and color indexes used to depict comprehensive surface
morphology comparisons. The actual calculation was
done using numeric values of the DEM.
The two most salient features on the morphological
maps of the glacier, in terms of DTMs from 1964 and
2006, include the following: (i) there was an elongated
lower surface or depression along the middle of the glacier in 1964 (Figs. 5a and 7a) as depicted by the light
green colour in the 4,950-4,990 m class range, and (ii) the
glacier surface above the elongated depression surface
was relatively steep in 1964, but subsequently melted out
causing substantial surface lowering in the area by 2006.
Topographic maps (Fig. 5) and DEMs (Fig. 7) clearly
show that the elevations of the debris-covered glacier
surface have substantially changed. A map of elevation
changes for the entire area (Fig. 8) was produced by
subtracting the DEM values for 2006 (Fig. 7b) from those
for 1964 (Fig. 7a). The values for elevation change are
presented in nine classes (Fig. 8). Extensive surface
lowering, e.g., as high as 156.9 m, is visible in the
up-glacier area, just up from the 2006 east lakeshore,
from melting of the steep glacier surface that existed in
1964. This characteristic is similar to that of the Imja
Glacier Lake (Lamsal et al., 2011).
The average lowering of the glacier surface (calculated for 3 × 3 m grids using the elevation change map,
Fig. 8) for the 42-year period from 1964 to 2006 over the
entire area is 37.5 m, with the average rate of surface
lowering being 0.9 m/year. Figure 8 clearly demonstrates
that surface lowering at the dead-ice and nearby area is
smaller, whereas the lowering gradually increases in the
up-glacier area and reaches its maximum in the uppermost area. This suggests that less glacier melting has
occurred in the down-glacier area when compared with
the up-glacier area.
The elevation change map in the lake area of 2009
(Fig. 9) was produced by subtracting the 2009 lake bottom values (bathymetric DEM, Fig. 6) from the 1964
glacier surface values (topographic DEM, Fig. 10b). The
surface lowering values are grouped into eight classes to
depict lowering extent. The average surface lowering for
the 45 years from 1964 to 2009 was 99.5 m at a rate of
2.2 m/year; the minimum and maximum surface lowering during this period were 12 m and 153.8 m, respectively. The explicit influence of a steeper surface gradient in
the upper part of the up-glacier area in the 1964 map, as
well as the deepest area in the 2009 bathymetric map, are
manifested in the elevation change map of the lake: i.e.,
greater surface lowering has occurred in the area specified above (Fig. 9).
The longitudinal profile L–L’ (Fig. 11) shows the
extent of the surface lowering along the glacier of 1964,
and the lake area and dead-ice area in 2006 together with
the steepness of the glacial surface gradient for both years.
Along profile L–L’ (Fig. 11), the maximum surface
lowering in the dead-ice area for the 42-year period from
89
Fig. 7 Digital Elevation Model (DEM) of the Chamlang South
Glacier in 1964 (a), and DEM for 2006 (b). Terrain
elevation values are grouped in eleven classes with the
same colors at 40 m intervals for each year. Red line
shows the lakeshore in 2006.
Fig. 8 Elevation change map showing the surface lowering of
the Chamlang South Glacier for 42 years from 1964 to
2006.
Fig. 9 Surface lowering from the glacier surface in 1964
(topographic DEM) to the lake bottom in 2009
(bathymetric DEM).
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T. SAWAGAKI et al.
a)
b)
Fig. 10 Topographic contour map (a) and DEM (b) of the 1964
glacier surface in the 2009 lake area, extracted from
Figs. 5a and 8 respectively.
1964 to 2006 was 29 m (from 4,954 m to 4,925 m), while
the maximum surface lowering in the lake area for
the 45-year period from 1964 to 2009 was 134 m (from
5,026 m to 4,892 m). Figure 5a clearly shows that the
area around the largest supraglacial pond had a low
surface gradient by 1964, and that there had already been
large melting, which favoured further lake expansion: the
relative height between the lake surface and the lateral
moraine (DGM of Sakai & Fujita, 2010) exceeded
100 m, so the lower area of the Chamlang South Glacier
in the 1960s can be categorized as a glacier of the type
‘with glacial lake’ of Sakai and Fujita (2010). The area
down-glacier from the pond melted less whereas the
steeper up-glacial area melted progressively more,
accelerating between 1964 and 2006. Considering the
steeper up-glacier surface and the water-surface level of
the largest supraglacial pond in 1964, it is suggested that
ice calving into the pond triggered the larger and faster
up-glacial lake expansion (Kirkbride & Waren, 1997;
Röhl, 2008; Fujita et al., 2009; Sakai et al., 2009). One
reason for low surface lowering in the dead- ice area as
well as non-downward lake expansion could be due to a
thicker debris cover there, as debris thickness increases
progressively down-glacier, hampering ice melting
(Mattson et al., 1993; Kayastha, 2000; Benn et al., 2001).
Thus, ice calving is undoubtedly a main mechanism of
lake expansion, especially for the further expansion of a
large glacial lake once it has formed. In contrast, direct
ice melting, including processes such as water-line
melting, aqueous and subaqueous melting, remain largely
significantly less influential than ice calving processes.
Subaqueous melting is also very small in the case of the
Imja glacial lake to the north (Fujita et al., 2009). If ice
calving had not been the main mechanism, downward
lake expansion in Chamlang South Tsho would have
been larger.
Profile A–A’ (Fig. 11) in the dead-ice area demonstrates that the glacial surface, even in 1964, was significantly lower than its lateral moraines, although the
glacial surface in the 1960s had been close to, or even
higher than, the lateral moraines in the lower area of the
Imja Glacier (Lamsal et al., 2011). Thus, the surface
lowering in the lower area of the Chamlang South Glacier
from 1964 to 2006 was small, suggesting that substantial
ice melting in the area had already occurred by 1964.
Profile B–B’ (Fig. 11) reveals that glacial ice melting
was less in the pond area, as well as the section towards
the left lateral moraine than the section towards the right
lateral moraine. In this particular profile section (Profile
B–B’), the glacier surface in 1964 was already considerably lower than the lateral moraines. Furthermore, the
undulating surface structure under the lake in 2006 seems
unlikely to indicate bedrock, thus suggesting that it most
probably consists of glacial ice and/or debris deposits on
the ice. Two other profiles C–C’ and D–D’ (Fig. 11)
exhibit progressively larger glacial surface lowering in
the up-glacial area.
Few studies reporting morphological changes of
glaciers (e.g., Bolch et al., 2008a) and glacial lakes (e.g.,
Lamsal et al., 2011) in the Nepal Himalaya exist, particularly those concerned with pre- and post-glacial lake
development and expansion as presented here. Prior to
the current study, no field research at the Chamlang
South Glacier had been conducted, so a comparison of
glacier surface lowering of the glacier and glacial lake to
its own previous period is not possible. However, the
glacier surface lowering at the Chamlang South Glacier
can be compared with two of the most thoroughly
researched glaciers in the same region, i.e., the Khumbu
and Imja glaciers (Bolch et al., 2008a; Lamsal et al.,
2011; Nuimura et al., 2011). The results found at the
Chamlang South Glacier agree well with the conclusions
of these studies. For example, Nuimura et al. (2011)
calculated a surface-lowering rate of 0.6-0.8 m/year in
17 years from 1978 to 1995 in the ablation area of the
Khumbu Glacier, and Bolch et al. (2011) also reported
0.5-1.2 m/year of surface lowering in the 40-year period
from 1962 to 2002 for the same glacier. Lamsal et al.
(2011) found surface lowering of the dead-ice and
up-glacier area of the Imja Glacier for the 42-year period
from 1964 to 2006 at the rate of 0.4 m/year and
1.1 m/year, respectively. Further, Fujita et al. (2009)
showed that the lowering rate of the dead-ice area of the
same glacier for the period from 2001 to 2007 was 0.06 to
1.03 m/year. Of particular interest is the fact that the rate
of lowering in the lake area of Imja Tsho for 38 years
was the same as that of the Chamlang South Tsho at
2.2 m/year. Furthermore, Fujita et al. (2009) estimate that
direct ice melting at the lake bottom of Imja Tsho for the
past several years is not significant. Therefore, the
evidence strongly suggests that the larger lowering rate
Changes in Surface Morphology and Glacial Lake Development of Chamlang South Glacier
91
Fig. 11 Cross sections (A–A’, B–B’, C–C’, D–D’) and a longitudinal section (L–L’) showing glacier
topographies in 1964 and 2006, and lake bathymetry in 2009.
of the Chamlang South Tsho is attributable to ice-calving
processes.
The applicability of repeat remote sensing data, especially DTMs, in the study of glacial lake dynamics has
been described elsewhere (e.g., Kääb, 2005; Surazakov
& Aizen, 2006; Fujita et al., 2008). Nevertheless, results
from this study are distinguished from the previous
research through the use of remote sensing data (e.g.,
Lamsal et al., 2011) in the representation of the glacial
morphology and surrounding terrain morphology, as well
as the documentation of changes over time. Clearly,
coarse resolution data such as ASTER and SRTM
(15/30 m and 90 m spatial resolutions, respectively)
inhibit the detection of micro-landform features (Fujita
et al., 2008). However, our research further demonstrated
and corroborated the previous conclusions of Lamsal
92
T. SAWAGAKI et al.
et al. (2011) concerning the use of high-resolution
Corona and ALOS data in the LPS platform, and its
production of sufficiently accurate DTMs and detailed
topographic maps that represent changes in glacier
surfaces, including micro-landform features such as
supraglacial ponds, ice cliffs, and moraine ridges.
Centre for Integrated Field Environmental Science’ at
Hokkaido University; the National Geographic SocietyWaitt Grant Programme, Washington, DC; The Mountain
Institute, Washington, DC; and Himalayan Research
Expeditions, Kathmandu, Nepal.
5. Conclusions
References
This study employed high-resolution Corona KH-4A
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photogrammetry system to generate DTMs. The produced DTMs, and subsequently derived topographic
maps, represented elevations and morphology of the
glacier surface in fine detail with a maximum error of
about +/- 10 m. Consistency among the produced DTMs
and topographic maps in the Chamlang South Glacier
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terminal moraine boundary. A maximum relative DEM
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A substantial glacier surface lowering occurred
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The area around the largest supraglacial pond in 1964
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Acknowledgements
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Nuimura of Nagoya University. We would also like to
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Takanobu SAWAGAKI
Takanobu SAWAGAKI is an Assistant Professor of
the Faculty of environmental Earth Science,
Hokkaido University. His major fields of study
are Glacial Geology, Quaternary Science and
Geographical Information Systems. He has broad
experience in circumpolar and alpine regions as a
member of Japanese Antarctic research expeditions, the Academic Alpine
Club of Hokkaido, and his own research expeditions in cold regions around
the world.
Damodar LAMSAL
Damodar LAMSAL obtained his Ph.D. at the
Graduate School of Environmental Science,
Hokkaido University, in September 2011. His
major areas of interest include modeling of
glacier surface morphology, glacial lake development, and evaluation of the potentiality of
glacial lake outburst floods (GLOFs) and their hazards. He has expertise in
geographic information systems (GIS) and remote sensing (RS), especially
digital photogrammetry.
Alton C BYERS
Alton C. BYERS, Ph.D., is a mountain geographer,
climber and photographer specializing in applied
research, integrated conservation and development programs. He received his doctorate
from the University of Colorado in 1987, focusing on landscape change, soil erosion, and
vegetation dynamics in Sagarmatha (Mt. Everest) National Park, Khumbu,
Nepal. He joined The Mountain Institute (TMI) in 1990 as Environmental
Advisor, and has since worked as Co-manager of the Makalu-Barun
National Park (Nepal Programs), Director of Appalachian Programs,
Director of TMI’s 400-acre Spruce Knob Mountain Center in West
Virginia, and Director of Science and Research at TMI since 2004.
Teiji WATANABE
Teiji WATANABE is a Professor of the Faculty of
Environmental Earth Science and the Graduate
School of Environmental Science, Hokkaido
University. Having a background in alpine geomorphology, he specializes in mountain geoecology, with interests in interaction of humangeo-ecosystems in high mountain areas and natural resource management
in protected areas. He has conducted extensive fieldwork in the Himalayas,
the Karakorums, the Alps, the Pamirs, and Japanese mountains.
(Received 20 November 2011, Accepted 13 March 2012)