Changes in Surface Morphology and Glacial Lake Development of Chamlang South Glacier in the Eastern Nepal Himalaya Since 1964

83 Changes in Surface Morphology and Glacial Lake Development of Chamlang South Glacier in the Eastern Nepal Himalaya since 1964 1* 2 3 1 Takanobu SAWAGAKI , Damodar LAMSAL , Alton C BYERS and Teiji WATANABE 1Faculty of Environmental Earth Science, Hokkaido University N10, W5, Sapporo, 060-0810, Japan 2Graduate School of Environmental Science, Hokkaido University N10, W5, Sapporo, 060-0810, Japan 3The 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 favorable (Reynolds, 2000; Quincey et al., 2007), i.e., exhibiting a glacier surface gradient of less than 2°, low Glaciers in the Hindu Kush-Himalaya have been ice velocity, and/or complete stagnation. Sakai and Fujita receding and melting since the end of the Little Ice Age (2010) discussed the importance of the glacial surface in 1850 (Fujita et al., 2001; Bolch et al., 2008a, 2011; lowering since the Little Ice Age. Glacier recession and Shrestha & Aryal, 2010; Fujita & Nuimura, 2011). One associated phenomena have multiple impacts and sig- of the consequences has been the formation and expan- nificances, all of which need to be considered in an inte- sion of glacial lakes, particularly during the last half grated manner (Haeberli et al., 2007; Hegglin & Huggel, century, as a result of glacial retreat that is most likely in 2008). Most importantly, an understanding of the reces- response to contemporary global warming and regional sion of debris-covered glaciers is absolutely necessary in warming trends (Yamada & Sharma, 1993; Mool et al., terms of hazards assessment, primarily because the 2001; Bajracharya et al., 2007; Watanabe et al., 2009). glacial lakes that form on them sometimes produce As a result, the potential for glacial lake outburst floods devastating GLOFs (Clague & Evans, 2000; Richardson (GLOFs) is increasing throughout the Hindu Kush- & Reynolds, 2000a, 2000b; Ives et al., 2010), which are Himalaya (e.g., Watanabe et al., 1994). often several times larger than normal climatic floods Supraglacial ponds and lakes are likely to form on the (Cenderelli & Wohl, 2001). GLOFs can cause wide- surface of debris-covered glaciers when conditions are spread damage and loss of life, property, infrastructure, Global Environmental Research ©2012 AIRIES 16/2012: 83-94 printed in Japan 84 T. SAWAGAKI et al. and the geomorphic environment (Ives, 1986; Vuichard complex geometry, lack metadata (ephemeris) pertaining & Zimmermann, 1987; Cenderelli & Wohl, 2003; to image acquisition, and require highly sophisticated Narama et al., 2010). A thorough understanding of image- processing software to extract 3D information. glacial recession is also critical to the estimation of the Despite this, Corona data provide an invaluable source glacier mass balance for water resource management for investigation in various fields such as glaciology and within a given region (Bolch et al., 2008b; Immerzeel archaeology. Detailed information on Corona and ALOS et al., 2010). PRISM data and their processing is described well by Mapping of glacier area change can be carried out Lamsal et al. (2011). with non-stereo orthorectified imagery; however, multi- During the past several decades in the Mt. Everest and date, stereo-capable data are required in order to calculate Makalu-Barun national parks of Nepal, 24 new glacial volumetric changes of glaciers, especially for the debris- lakes have formed and 34 major lakes are reported to covered type. Multi-date stereo-images with long-period have grown substantially as a result of climate change time differences as well as high spatial resolution are and regional warming trends (Bajracharya et al., 2007). needed to produce accurate and detailed 3D topographic Recent analyses of comparative satellite imagery have or terrain maps, that in turn can expand our under- suggested that at least twelve of the new or growing lakes standing of the morphological changes of a glacier’s within the Dudh Kosi watershed, nine of which are surface. Photographic products from the Corona program located in the remote Hongu valley of Makalu-Barun (~1960 to 1972) are the oldest remote sensing stereo National Park, are ‘potentially dangerous’ based on their images publicly available with a wide geographic rapid growth over the past several decades (Bajracharya coverage and high spatial resolution (~1.8 to 7.6 m). et al., 2007; Bajracharya & Mool, 2009). However, Likewise, the Advanced Land Observing Satellite despite the large amount of national and international (ALOS) PRISM, is a relatively new remote sensing media attention recently generated by these new and/or satellite program (launched in 2006) that has stereo growing lakes in the Hongu valley, relatively little was capability capable of generating digital terrain models known about them in 2009 because of their extreme (DTMs) and 3D maps, and which also offers high spatial remoteness and difficult access. resolution stereo-data (2.5 m). Several studies have In response, we carried out the first scientific field investigated volumetric changes in glaciers in the investigation of these glacial lakes in October-November Himalaya using either Corona or ALOS data (e.g., Bolch of 2009 (Fig. 1). At the time, a glacial lake situated at the et al., 2008a; Lamsal et al., 2011). Corona data have a 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 85 among the most dangerous of the nine ‘potentially Chamlang South Tsho has developed rapidly between dangerous’ lakes within the valley (Mool et al., 2001; 1964 and 2000 on the debris-covered Chamlang South Bajrachayra et al., 2007; ICIMOD, 2011), prompting the Glacier (Fig. 2). The altitude of the lake surface is research team to focus its activities on the Chamlang 4,940 m. South Glacier while conducting preliminary analyses of the other eight lakes. Respecting its positional relation- 3. Data and Methods ship with the peak, we call this lake ‘Chamlang South Tsho’ although it has been referred to by various other 3.1 Image processing names. The aim of our study was to examine changes in Two sets of stereo-data (ALOS PRISM and Corona) surface morphology of the Chamlang glacier and the lake with a time span of over four decades were used. ALOS between 1964 and 2006. PRISM data (acquired on 4 December 2006; Path: 140, Row: 41, spatial resolution: 2.5 m) with processing level 2. Study Area 1B1 (radiometrically calibrated data) plus Rational Polynomial Coefficient (RPC) data files were obtained Chamlang South Tsho (longitude: 86˚57’33”E, lati- from the Remote Sensing Technology Center of Japan tude: 27˚45’24”N), has been called different names by (RESTEC). ALOS PRISM acquires data in triple mode F, different researchers, e.g., Chamlang Tsho in the 1:50000 N, and B (forward, nadir, and backward). With these data, Schneider map, Chamlang Pokhari by Byers et al. (2012), <10 m geometric accuracy is achievable (Tadono et al., and most commonly West Chamlang in the 1:50000 topo- 2009). graphic map by the Survey Department of Nepal and in Images acquired from Corona camera systems KH-1, Mool et al. (2001) and Bajracharya et al. (2007), which KH-2, KH-3, KH-4, KH-4A, and KH-4B were declassi- also provided an identification number of kdu_gl 466. fied in 1995 and became available in a digital format in Mt. Chamlang has two glacial lakes on the westward side 2003 (McDonald, 1995; Galiatsatos et al., 2008). The of the peak: one in the northwest, with no local name but early systems of KH-1, KH-2, and KH-3 were equipped an identification number of kdu_gl 464 (Bajracharya with a single panoramic camera, while the latter systems et al., 2007), and the other in the southwest region of the of KH-4, KH-4A, and KH-4B were equipped with both peak (Fig. 1). To avoid confusion, we propose the use of forward- and backward-looking cameras. The images the name of Chamlang South Tsho for the lake located in taken by the KH-4, KH-4A, and KH-4B camera systems, the southwest region.

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