Natural Resources, 2013, 4, 449-455
Published Online November 2013 (http://www.scirp.org/journal/nr)
http://dx.doi.org/10.4236/nr.2013.47055
Open Access NR
449
Changes in Imja Lake and Karda Lake in the Everest
Region of Himalaya
Wenbo Chen1*, Tomoko Doko2,3, Hiromichi Fukui4, Wanglin Yan1
1Graduate School of Media and Governance, Keio University, Fujisawa, Japan; 2Research Institute of Environment and Information
Sciences, Yokohama National University, Yokohama, Japan; 3Research Fellow of the Japan Society for the Promotion of Science,
Tokyo, Japan; 4Chubu Institute for Advanced Studies, Chubu University, Kasugai, Japan.
Received August 24th, 2013; revised September 27th, 2013; accepted October 12th, 2013
Copyright © 2013 Wenbo Chen et al. This is an open access article distributed under the Creative Commons Attribution License,
which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.
ABSTRACT
The Himalaya is a region sensitive to climate change. Changes in the glacial regime are one indicator of global climate
changes. There are several studies focusing on analysis of temporal changes of these glacial lakes in the Himalaya re-
gion. However, the researches on addressing these trends in relation with surrounding topographical conditions are quite
limited. In this study, we analyzed spatio-temporal changes in Imja Lake, located on the southern slope, and Karda Lake,
located on the northern slope of the Mt. Everest region, in 1976, 1992, 2000, and 2008. Moreover, we examined whe-
ther the topographic conditions differ between the two slopes. Landsat and ASTER GDEM (advanced space borne ther-
mal emission and reflection radiometer, global digital elevation model) data were used to identify boundaries of target
glacial lakes and to calculate three indices of growth rate compared to year of 1976 (%, GRa), growth rate compared to
preceding year (%, GRb), and growth speed (m2/year, GS) of the two lakes. The topographic conditions in circular
buffer zones from the centroid of the two lakes were analyzed. Although the area of two lakes demonstrated linear in-
crease from 1976 to 2008, growth rate compared to year of 1976 (GRa) differed significantly (Kruskal-Wallis test, p <
0.05). The area of Imja Lake enlarged significantly faster than the one of Karda Lake (Kruskal-Wallis test and Chi-
squared test for independence on m × n contingency table between 1976, 1992, 2000, and 2008 on growth speed (GS)).
The two slopes differed in terms of three topographical variables: altitude, aspect, and angle of inclination (Kruskal-
Wallis test, p < 0.05). The differences between the growth trends of the two lakes can be explained by differences in the
topographic conditions on their respective slopes. However, differences in temporal changes should be explained by
other temporal factors, e.g. climatic variables.
Keywords: Glacial Lakes; Topography; Himalaya; Remote Sensing; GIS
1. Introduction
The Himalaya is well known for its high altitude, frigid
temperatures, high wind speeds, thin air, and remoteness.
The physiography of the Himalaya is characterized by a
complex network of mountains and valleys [1]. Sharp ri-
dge crests and deep valleys are its main characteristics
[1]. These characteristics may influence changes in its gla-
cial regime.
Since the last century, most Himalayan glaciers have
melted at a rate that ranges from a few meters to several
tens of meters per year [2]. These changes directly af-
fected the formation and enlargement of downstream
glacial lakes, often resulting in a glacial lake outburst
flood (GLOF) [3-8]. Thus, identifying and monitoring
changes in glacial lakes become important in under-
standing of the regional environment and local ecosys-
tems.
Several studies have focused on the trend of growing
glacial lakes in the Himalaya region. However, few of
the studies address these trends in a context of the sur-
rounding topographic conditions of the target lakes.
The objectives of this study were (a) to analyze spa-
tio-temporal differences in the trends of changes in Imja
Lake, located on the southern slope, and Karda Lake, lo-
cated on the northern slope of the Himalayan range dur-
ing four time periods, i.e., 1976, 1992, 2000, and 2008
and (b) to examine whether the topographic condi-
*Corresponding author.

Changes in Imja Lake and Karda Lake in the Everest Region of Himalaya 450
tions differ between the northern and southern slopes of
the Mt. Everest region.
2. Methods
2.1. Study Area
The study area is located in the Mt. Everest region, Hi-
malayan range. The northern slope is located in China,
and the southern slope is located in Nepal (see Figure 1).
The target glacial lakes are Karda Lake, located on the
northern slope, and Imja Lake, located on the southern
slope.
Karda Lake is located in Tibet, China, on the northern
slope of Mt. Everest. The altitude of Karda Lake is 5,643
m; the latitude and longitude are 28˚4.28' and 87˚3', re-
spectively. Karda Lake is a moraine lake, which was a
smaller pond at the snout of Karda Glacier in 1925 [9].
Accessing Karda Lake is extremely difficult, and hence
previous studies of Karda Lake are limited. The year
when Karda Lake started to expand is not known.
Imja Lake (lat./long. 27˚4'/86˚5.4', altitude 5010 m) is
located in the Dudh Koshi Basin of Nepal, on the south-
ern slope of Mt. Everest. Imja Lake did not exist in the
early 1960s [2]. Instead, only several smaller supraglacial
ponds were present in this location. Imja Lake began
growing in 1975 due to glacial melting. Its surface area
expanded from 0.30 km2 in 1975 to 0.85 km2 in 2000 [2].
It has been identified as one of the lakes displaying the
greatest potential for a GLOF now in the Nepalese part
of the Himalaya [10]. Imja Lake has been relatively stud-
ied as it is easier to access and it is concerned due to its
faster expansion.
Figure 1. Study area.
2.2. Data Sources
Satellite images with minimal obstruction by clouds and
snow coverage were used in this study. These images
were from the Landsat MSS from December 1976, with a
spatial resolution of 60 m, the Landsat TM from Novem-
ber 1992, with a spatial resolution of 30 m, the Landsat
ETM + from October 2000, with a spatial resolution of
30 m, and the ASTER from January 2008, with a spatial
resolution of 15 m. For the terrain analysis, ASTER Glo-
bal DEM data were downloaded from the ASTER GDEM
website.
2.3. Identification of Glacial Lakes
Figure 2 presents the flowchart of the study. First, the
NDWI (normalized difference water index) was calcu-
lated to allow identification of water bodies from the
Landsat satellite images. NDWI is defined as the differ-
ence of reflectance observed in the green band and the
NIR band divided by the sum of the two reflectance val-
ues [11]. The value of this index ranges from −1 to +1.
Second, a model of the terrain was developed from a
digital elevation model (DEM) derived from the ASTER
GDEM data. Based on our previous field work in the
Himalaya and Tibet, China, it was recognized that the
angle of inclination that allowed drainage of melt water
had gradients greater than 10˚. Study in Bhutan [12] and
study in China and Nepal [13] reported similar observa-
tions. Thus, a threshold value of a ground angle of incli-
nation of 10˚ (maximum) was adopted in this study.
Finally, the boundaries of two glacial lakes were iden-
tified by integrating the NDWI and angle of inclination
criteria. The satellite imagery analysis and data process-
ing were performed using ENVI® 4.7.
2.4. Trends of Changes in the Two Glacial Lakes
First, the surface areas of Imja Lake and Karda Lake dur-
ing the four time periods in the years 1976, 1992, 2000,
and 2008 were calculated in m2 and coded as Alake.year.
The variable lake was coded as either “Imja” or “Karda”,
and the year was coded as 1976, 1992, 2000, or 2008.
For example, AImja.1976 denotes the surface area of Imja
Lake in 1976.
Second, based on the surface areas of the glacial lakes,
three indices were developed: 1) the growth rate of the
area of a particular lake compared to its area in 1976 was
defined as GRa.lake.year (%), for example, GRa.Imja.1992 =
AImja.1992 / AImja.1976 * 100, whereas GRa.Imja.1976 = 100; 2)
the growth rate of the area of a lake compared to that of
the lake in the preceding time interval was defined as
GRb.lake.year (%), for example, GRb.Imja.2008 = AImja.2008 /
AImja.2000 * 100; and 3) the growth speed of a lake was de-
fined as the expanded area per year between consecutive
time periods and was code as GSlake.year (m2/year),
d
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Changes in Imja Lake and Karda Lake in the Everest Region of Himalaya
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451
Figure 2. Flowchart of the method.
between China and Nepal was assumed to represent the
crest of the mountain range in this study. The lake closest
to this boundary was Imja Lake, which is located 6.7 km
from the boundary. Second, a buffer zone around the
centroid point of a target lake was generated for each
lake, using a radius of 6.7 km. Finally, the topographical
variables inside the buffers around the two lakes were
evaluated based on the ASTER GDEM data using ArcMap
ver. 10®. The slope aspect was measured clockwise in
degrees from azimuth 0, due north, to 360, again due north,
coming full circle. The value of each cell in an aspect
dataset indicates the direction of the cell’s slope face. Le-
vel areas having no downslope direction were given a va-
lue of −1.
for example, GSImja.2008 = (AImja.2008 − AImja.2000) / (2008 −
2000).
Third, the trends of changes in the two glacial lakes
were analyzed using a bar chart and a line chart. For
comparison purposes, the data were aggregated in 8-year
time intervals. Because the interval from 1976 to 1992
spanned 16 years, the surface area in 1984 was interpo-
lated to the mean value between 1976 and 1992, defined
as Alake.1976 + (Alake.1992 − Alake.1976) / 2.
Fourth, two statistical tests were applied. The Krus-
kal-Wallis test was applied to examine if there is a signi-
ficant difference (p < 0.05) between the two lakes regar-
ding the three indices, GRa.lake.year (%), GRb.lake.year (%),
and GSlake.year (m2/year). The Chi-squared test for inde-
pendence on an m x n contingency table was applied to
test for independence between the time periods and the
two lakes regarding the three indices (p < 0.05). These
statistical analyses were conducted using Microsoft Ex-
cel 2010.
The distribution of the three topographical variables
was examined using histograms. Descriptive statistics
were calculated for each variable. The topographical dif-
ferences between northern and southern slopes were test-
ed using the Kruskal-Wallis test (p < 0.05). These statis-
tical analyses were conducted using the software R, ver-
sion 2.13.2.
2.5. Topographic Conditions on Northern and
Southern Slopes 3. Results
We hypothesized that the changes in the two lakes are
influenced by their positions on the two different slopes
(northern slopes and southern slopes) of the Mt. Everest
region. To address the potential differences in topogra-
phic conditions between the two lakes, three topographi-
cal variables, which are their altitude, angle of inclination,
and aspect, were calculated. First, the distance from the
centroid of a lake to the international boundary was cal-
culated using ArcMap ver. 10®. The international boundary
3.1. Trends of Changes in the Two Glacial Lakes
Map comparison during the 32 years showed that both
Imja Lake and Karda Lake were generally increasing
(see Figure 3). The surface areas (m2) of the two glacial
lakes in 1976, 1992, 2000, and 2008 are summarized in
Table 1. The surface area of Imja Lake expanded by
574,104 m2 from 1976 to 2008, and the surface area of
Karda Lake expanded by 287,957 m2.

Changes in Imja Lake and Karda Lake in the Everest Region of Himalaya 452
Figure 3. Changes in Imja and Karda Lakes.
The trends of the changes in the two glacial lakes were
plotted with regard to the growth rate (Figure 4) and
growth speed (Figure 5). The growth rate compared to
year of 1976 (GRa.lake.year) of both lakes displayed linear
increases beginning in 1976 (Figure 4; line chart). How-
ever, the growth rate compared to preceding year of both
lakes, GRb.lake.year (%) (Figure 4; bar chart), displayed
downward trends over time. The growth speed, GSlake.year
(m2/year), of both lakes declined over time (Figure 5).
Table 2 shows results of statistical tests to examine
differences between Imja Lake and Karda Lake. The
Kruskal-Wallis test revealed a significant difference (p <
0.05) between the two lakes regarding the GRa.lake.year in-
dex (%; T = 3.85, f = 1) and the GSlake.year index (m2/year;
T = 3.85, f = 1) but not regarding the GRb.lake.year index (%;
T = 1.19, f = 1). On the other hand, the Chi-squared test
for independence on the m × n contingency table (p <
0.05) demonstrated a relationship between the time peri-
ods and GSlake.year (m2/year; T = 349.82, f = 2, m = 2, n =
3) index but none between the time periods and the
GRa.lake.year (%; T = 2.03, f = 2, m = 2, n = 3) nor
GRb.lake.year (%; T = 2.81, f = 2, m = 2, n = 3) indices.
3.2. Topographic Conditions of Different Slopes
Table 3 presents descriptive statistics of the topography
(aspect, angle of inclination, and altitude). Figure 6 pre-
sents the values of these three variables in histogram
form. The findings indicate that the northern slope had a
mean southeast aspect (154.3 degrees), whereas the
Table 1. Changes in lake surface area.
Area (m2) Year Imja Lake Karda Lake
1976 284,411 389,317
1992 567,360 550,732
2000 724,365 623,236
2008 858,515 677,274
southern slope had a southwest aspect (194.1 degrees).
Although the mean altitude of the southern slope (5,530
m) was lower than that of the northern slope (5,878 m),
its angle of inclination was steeper (mean angle of incli-
nation = 27.3 degrees) than that of the northern slope
(mean angle of inclination = 19.8 degrees).
There were significant topographical differences (Krus-
kal-Wallis test, p < 0.05, df = 1) between the northern
and southern slopes with regard to their aspect (Kruskal-
Wallis chi-squared = 14622.1, p < 2.2e - 16), altitude
(Kruskal-Wallis chi-squared = 66969.65, p< 2.2e - 16),
and angle of inclination (Kruskal-Wallis chi-squared =
14639.19, p < 2.2e - 16).
4. Discussion
Our statistical analysis (Figures 4 and 5, Table 2, Krus-
kal-Wallis test) revealed significant differences between
the two lakes in terms of their growth rates, GRa.lake.year
(%), and growth speed, GSlake.year (m2/year). There was no
difference between the growth rate compared to pre-
ceding year, GRb.lake.year (%), of the two lakes. Although
the two lakes exhibited a linear trend of enlargement
from 1976 to 2008, their rates of growth differed signifi-
cantly. The growth rate of Imja Lake was much greater
than that of Karda Lake. On the other hand, their rates of
expansion displayed a downward trend over time. The re-
cent changes, i.e., between 2000 and 2008, were smaller
than those between 1976 and 1984. These downward trends
were consistent in both of the lakes.
The differences between Imja Lake and Karda Lake
can be explained by differences in the topographic condi-
tions between the southern and northern slopes. Our spa-
tial buffer analysis and statistical analysis revealed that
the northern and southern slopes differ with regard to the
three topographical variables of altitude, aspect, and an-
gle of inclination (Figure 6, Tables 2 and 3, Kruskal-
Wallis test). The difference in altitude is considered to
have influenced the development of the glacial lakes. Ge-
nerally, the temperature decreases 0.65˚C per 100 m of
elevation increase in the high mountains. This generali-
zation implies that the environment of Karda Lake is
colder than that of Imja Lake. Second, the difference in
aspect affects the level of solar heating. Heating is great-
est on southwest-aspect slopes [14], which may cause
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Changes in Imja Lake and Karda Lake in the Everest Region of Himalaya
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453
Figure 4. Trends in growth rates of lake surface area.
Figure 5. Trends in growth speed of lake surface area.
Table 2. Results of statistical tests to examine differences between Imja Lake and Karda Lake.
(A) Temporal data analysis
Kruskal-Wallis test for
a whole time period
Chi-squared test for independence on m × n
contingency table between 1976, 1992, 2000, and 2008
Growth rate compared to year of 1976 (GRa) T = 3.85, f = 1* T = 2.03, f = 2, m = 2, n = 3 (No difference)
Growth rate compared to preceding year (GRb) T = 1.19, f = 1
(No difference) T = 2.81, f = 2, m = 2, n = 3 (No difference)
Growth speed (GS) T = 3.85, f = 1* T = 349.82, f = 2, m = 2, n = 3*
(B) Non-temporal data analysis: analysis on topographic conditions
Kruskal-Wallis test
Altitude Aspect Angle of inclination
Imja Lake
Karda Lake
Kruskal-Wallis chi-squared
= 66969.65, p < 2.2e - 16*
Kruskal-Wallis chi-squared
= 14622.1, p < 2.2e - 16* Kruskal-Wallis chi-squared = 14639.19, p < 2.2e-16*
Note. *means there is a significant difference between two lakes (p < 0.05).

Changes in Imja Lake and Karda Lake in the Everest Region of Himalaya 454
Table 3. Summary of aspect, angle of inclination, and altitude.
Slope Parameter North South
Min −1 −1
Mean 154.3 194.1
Max 359.8 359.9
Aspect (degree)
SD 101.28 93.99
Min 0 0
Mean 19.8 27.3
Max 68.54 81.47
Angle of inclination (degree)
SD 11.64 17.07
Min 5102 4522
Mean 5878 5530
Max 7173 7930
Altitude (m)
SD 283.72 526.43
Figure 6. Aspect, angle of inclination, and altitude on northern and southern slopes.
Imja Lake (southwest aspect) to receive greater heating
than Karda Lake (southeast aspect). Third, the southern
slope is steeper than the northern slope. This difference
in angle of inclination may cause glacial melt water to
concentrate and accumulate in relatively level areas
downstream. Finally, because the windward side of the
mountain range may receive more air moisture than the
leeward side [15,16], the southern slope may receive
more precipitation than the northern slope. The interac-
tion between all of these factors is considered to cause
the difference in the growth trends of the two glacial
lakes.
On the other hand, our statistical analysis of the tem-
poral changes during the four time periods in the years
1976, 1992, 2000, and 2008 (Chi-squared test) revealed a
relationship between the time periods and growth speed
(Table 2). These phenomena cannot be explained by
changes in topographic conditions on the northern and
southern slopes because the topographic conditions are
usually stable over time. To address this issue, environ-
mental variables that are affected by temporal changes
should be considered. We assume that climatic variables
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Changes in Imja Lake and Karda Lake in the Everest Region of Himalaya 455
could explain the temporal changes of the rates of expan-
sion of these two lakes. Available climatic data are cur-
rently quite rare because the extreme conditions in the
Himalaya region make it extremely difficult to build me-
teorological stations there. Future studies require a cli-
matic model to allow analysis of the temporal changes of
the glacial lakes caused by climate variables.
5. Acknowledgements
The authors are thankful to the Global Earth Observation
Grid, Japan, for providing the ASTER data via the GEO
Grid project, which was developed with the goal of pro-
viding an E-Science infrastructure to the worldwide earth
sciences community. Funding for this research was pro-
vided by the Research Promotion Fund in Remembrance
of Mori Taikichiro in 2011, 2012, and 2013 of Keio Uni-
versity, and Kurita Water and Environment Foundation,
in 2013.
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