Recent Changes in Glacier Tongues in the Langtang Khola Basin, Nepal, Determined by Terrestrial Photogrammetry

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1 Snow and Glacier Hydrology (Proceedings of the Kathmandu Symposium, November 1992). IAHSPubl. no. 218, Recent Changes in Glacier Tongues in the Langtang Khola Basin, Nepal, Determined by Terrestrial Photogrammetry G. KAPPENBERGER 1, U. STEINEGGER 2, L. N. BRAUN 2 & R. KOSTKA 3 1 Swiss Institute of Meteorology, Osservatorio Ticinese, CH-6605 Locarno Monti, Switzerland 2 Swiss Federal Institute of Technology ETH, Winterthurerstr. 190, CH-8057 Zurich, Switzerland 3 Institute for Applied Geodesy and Photogrammetry, Technical University, Steyrergasse 30, A-8010 Graz, Austria Abstract Changes in the position of glacier tongues reflect the mass balance conditions of past years. A general advance or retreat of glaciers indicates a corresponding change in weather or climate. Changes in glacierized area, in turn, will influence glacier runoff. An analysis of aerial or terrestrial photographs by means of digital image processing allows inferences to be made about glacier fluctuations, even in areas where no accurate geodetic surveys are available over longer time periods. An approximative determination of the displacement of five glacier tongues in the Langtang Khola basin was made for the period between 1980 and The results show that only small fluctuations occurred on south-facing glaciers. Meanwhile, glaciers on north-facing slopes advanced. There is some evidence that this advance took place for the most part after A possible explanation of the aspect-dependent behaviour of glacier terminus changes is given. INTRODUCTION Discharge from glaciated basins of the Himalayas plays an important role, for instance in the maintaining of a relatively high base flow during the dry winter season, most likely due to melting at the base of the glaciers (Motoyama et al., 1987; Braun et al., 1993). Changes in glacierization may alter runoff of a basin to a great extent (see Chen 1991, for alpine conditions). An optimal use of water resources calls for sufficient quantitative glacio-hydrological information. In this contribution a possible application of remote sensing, employing terrestrial photogrammetry, is given. The aim of this investigation was to determine changes of glacierization and their possible consequences for runoff production. Changes of the length and area of glaciers give valuable indications of climatic variations. Changes in accumulation and/or ablation conditions may

2 96 G. Kappenberger et al. cause changes in the position of the terminal position and glacierized area after a response time specific to the glacier considered. This response time may be as long as a quarter of a century for long valley glaciers (e.g. Grosser Aletsch Glacier, Switzerland). A thick debris cover as typical for Himalayan valley glaciers may prolong the response time considerably due to a strong reduction of ablation at the glacier surface. Small and clean kar-glaciers, on the other hand, have a typical response time of one to a few years. With the available images covering only 10 to 20 years' time interval good results could be expected for rather small glaciers without extensive debris-cover. The goal of glacier cartography is the presentation of different glacial phenomena in cartographic form, and the mapping of snow and ice bodies (Williams, 1986). In the study area of Langtang Himal (Fig. 1) the valley glaciers are mostly debris-covered. The old lateral and terminal moraines are well defined in most cases, but the existing images cannot give reliable information on the current position of ice borders. Slope glaciers free from debris cover, however, generally show well defined ice edges. The determination of glacier fluctuations during the past decades can be carried out favourably for this type of glaciers using remote sensing methods. A rather simple method for the detection of glacier fluctuations consists in the watershed boundary or mountain ridge trail gauging station o town, Kharka glacier terminus nvestigated Langtang Li rung 7234 Langtang Glacier 5 km P3Tithang Karpo N I Langtang Gangtsa j La 5122 Gangchenpo 6387 Fig. 1 Location map of Langtang region, where recent changes in glacier tongues were determined by terrestrial photogrammetry. Elevations based on the map of the Austrian Alpine Club (1990).

3 Recent changes in glacier tongues in the Langtang Khola basin 97 comparison of images by means of digital image processing. The result is a visualization of the changes between the times when the images were taken. Glacier fluctuations in the Langtang valley The first investigations on glacierization and the movement of glaciers in the Langtang region were done in the 1960s. Since then, some glaciers were monitored sporadically (Watanabe & Higuchi, 1987). Numerous contributions have been published on Yala Glacier (see for instance Ono, 1985). A continuous observation series for Yala Glacier between 1982 and 1989 is given by Yamada et al. (1992). A glacier inventory was established by Shiraiwa & Yamada (1991). Historic glacier positions were studied and dated by Shiraiwa & Watanabe (1991). Our observations are aimed at contributing some information on strongly differing glaciers over the last years. For this purpose high quality terrestrial images were taken as a reference at a scale as large as possible in the area in question (Table 1, Figs 2-4). Photos taken at a later date were transformed onto these reference images with the aid of clearly identifiable points in the immediate area in question. Resulting from this process are scanned images of the time-series digitally transformed onto the reference image. For a final statement concerning the glacier changes, the well-defined ice margins and the available identifiable details were employed. As a measure of the glacier changes the relative displacement of the ice margin is given. The approximate scale allows the estimation of the absolute value of the displacement. RESULTS For each of the 5 glaciers as shown in Fig. 1 and Table 1 the changes in position of the glacier fronts were evaluated using the method described above. The results are summarized graphically in Figs 2-4. Cones of ice avalanches and uncertain ice borders were not considered in this analysis. The south-facing glaciers (Fig. 2) can be regarded as stationary. For Yala Glacier our finding is in accordance with Yamada et al. (1992) who report a mean advance of 2.6 m between October 1982 and September 1987, and a mean retreat of 4.0 m between 1987 and 1989 based on eight reference points. The two glaciers on north-facing slopes (Fig. 3) show a clear advance of the ice borders. In the case of Gangtsa La Glacier the maximal advance is about 50 m, and for Gangchenpo West Glacier about 30 m. There is evidence that the main advance took place after 1984 here. The considerable retreat of the Pemthang Karpo West Glacier (Fig. 4) can be explained by large ice break-offs. This fact is indicated by the steepness of the slope and the large avalanche cone below the ice front. As a result, the variation of this ice edge is not caused by meteorological or climatological conditions.

4 98 G. Kappenberger et al. Table 1 Details on the glacier termini investigated (inventory numbering based on Shiraiwa & Yamada, 1991). Glacier Inventory: ID No. Kyimoshung (Khymjung) L090 Yala L110 Gangtsa La L520 Gangchenpo West L410 Pemthang Karpo West L310 Height of terminus (m asl) Glacier exposition Orient, of image Approx. scale at ice edge Reference level and ice edge Glacier front Activity 4360 South Northwest 1: , 1991 lobed stationary Southwest Northeast 1: lobed stationary North South 1: lobed advance Northwest Southeast 1: , 1991 lobed advance 5200 West East 1: calving uncertain Measurements carried out by means of remote sensing have not shown significant changes of the debris-covered glacier tongues over the last twenty years. The oldest image documents used go back to Erwin Schneider's terrestrial photogrammetric and aerial photographs taken in 1970 and in Profile measurements across Lining Glacier performed in March 1991 and 1992 indicate that this heavily debris-covered valley glacier has lost considerable mass in the tongue area (see Fig. 1). Despite of a stationary glacier terminus this glacier is not in a stationary state. Future investigations on further valley glaciers should be encouraged in order to discover whether these also show aspect-related and other differences. -~ < &%*"*,T %'sf: v r : *y l Ï'.. iyçtf.s^x' Fig. 2 Reference level and ice edges of Kyimoshung (left) and Yala (right) Glaciers, both generally oriented towards South and showing no significant changes in glacier terminus position between 1980 and See also Table 1 for physiographical details.

5 Recent changes in glacier tongues in the Langtang Khola basin 99 Fig. 3 Reference level and ice edges of Gangtsa La (left) and Gangchenpo West (right) Glaciers, both generally oriented towards North and showing a noticeable advance of the glacier terminus position between 1980 and Possible explanation and conclusions Here, a speculative attempt is made to explain the aspect-dependent behaviour of the changes of glacier terminus positions in the Langtang. It is well understood that possible climatic changes have different effects depending on the spatial and temporal scale considered. As a first step, the following points could be of interest: - The global warming of the atmosphere also affects the Himalayan region. This could result in a general reduction of snow cover extent. ' ' > % * * " * \?- Fig. 4 Reference level and ice edges of Pemthang Karpo West Glacier, oriented towards West and calving. The large retreat of the terminus position between 1980 and 1991 is due to ice break-off, and therefore not directly related to climatological conditions.

6 100 G. Kappenberger et al. - As a consequence, the albedo of the region is reduced, heating is increased due to larger absorption of solar radiation, and stronger thermal winds (slope and valley winds) develop. - In north-south oriented valleys the effect of a changed thermal wind system are symmetrical. In east-west oriented valleys, however, the effect is asymmetrical: as south-facing slopes receive more radiation, more heating and a stronger wind component occur on south-facing slopes compared with north-facing ones (see Fig. 5). - Stronger thermal winds also tend to increase the dust content in the air. As a result, more dust is deposited on the surface of south-facing slopes, causing a lower albedo and increased melting as compared to north-facing ones. - Stronger thermal winds also increase the formation of cumulus clouds. Larger clouds are situated slightly shifted further to the North of ridges oriented from East to West due to the different wind increase (up-slope winds are stronger over south-facing slopes as compared to north-facing ones). As a consequence, north facing glaciers get more shadow and more snow showers, resulting in a higher albedo and reduced melting. Fig. 5 Schematic diagram of a valley oriented from East to West (as for example the Langtang valley near Kyangjing) showing differences in slope and valley winds as well as the formation of convective clouds under normal snow cover conditions (left) and under a reduced snow cover extent (right). The combination of these effects tends to increase the mass of north-facing glaciers and may explain the general advance of their tongues. Further assessments of glacier mass balances as shown by Shiraiwa et al. (1992) will help to test whether these effects also increase the mass balance gradient of the glaciers in the Langtang area, as could be expected. Acknowledgements Logistic support in the field was provided by the German Agency for Technical Cooperation (GTZ, Dr. W. Grabs) and the Department of Hydrology and Meteorology (DHM) of his Majesty's Government of Nepal

7 Recent changes in glacier tongues in the Langtang Khola basin 101 (Mr. A. P. Pokhrel and his staff). All their contributions are gratefully acknowledged. REFERENCES Austrian Alpine Club (1990) Expedition maps AlpenvereinskarteLangthang Himal 1:50 000, Nr. 0/10 (West) and Nr. 0/11 (Ost), printed by Freytag-Berndt and Artaria, Vienna. Braun, L. N., Grabs, W. & Rana, B. (1993) Application of a conceptual precipitation-runoff model in the Langtang Khola Basin, Nepal Himalaya. IAHS Publ., this volume. Chen, J. (1991) Changes of Alpine climate and glacier water resources. Ziircher Geographische Schriften, Heft 46, Department of Geography, Swiss Federal Institute of Technology (ETH), Zurich, 196 pp. Motoyama, H., Ohta, T. & Yamada, T. (1987) Winter runoff in the glacierized drainage basin in Langtang Valley, Nepal Himalayas. Bull, of Glacier Research 5, Japanese Society of Snow and Ice, Ono, Y. (1985) Recent fluctuations of the Yala (Dakpatsen) Glacier, Langtang Himal, reconstructed from annual moraine ridges. Z. fur Gletscherkunde und Glazialgeologie 21, Shiraiwa, T. & Watanabe, T. (1991) Late Quaternary glacial fluctuations in the Langtang valley, Nepal Himalaya, reconstructed by relative dating methods. Arctic and Alpine Res. 23(4) Shiraiwa, T. & Yamada, T. (1991) Glacier inventory of the Lantang Valley, Nepal Himalayas. Low Temperature Sci., Ser. A 50, Data Report, Shiraiwa, T., Ueno, K. & Yamada, T. (1992) Distribution of mass input on glaciers in the Langtang valley, Nepal Himalayas. Bulletin of Glacier Research 10, Watanabe, O. & Higuchi, K. (1987) Glaciological studies in Asiatic Highland region during Bull, of Glacier Research 5, Williams, R. S. (1986) Glaciers and glacial landforms. In: Geomorphology from Space - a Global Overview of Regional Landforms (ed. by N. M. Short & R. W. Blair), NASA SP-486, Washington, DC. Yamada, T., Shiraiwa, T., lida, H., Kadota, T., Watanabe, T., Rana, B., Ageta, Y. & Fushimi, H. (1992) Fluctuations of glaciers from the 1970s to 1989 in the Khumbu, Shorong and Langtang regions, Nepal Himalayas. Bull, of Glacier Research 10,

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