Monitoring of supra glacial lakes and risk assessment of their outburst in the Greet Himalayas.

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The inventory of present moraine dammed glacier lakes with the area more than 0.01km^2 in the northern and southern slopes of the Great Himalayas in the longitude between 85°15′ and 91°00′E, i.e., eastern Nepal, Sikkim, India, Bhutan and Tibet, China was made by using the latest Landsat ETM imageries taken in 2000, 2001 and 2002. Totally 539 lakes with the whole ares of 122.46km^2 are compiled in this area. The lakes were also compiled using Landast MSS imageries taken in 1976 and compared with the lakes found in the 2000-2002 imageries to clarify their temporal variations during 24-26 years. The results indicate that all lakes in 1976 expanded and many lakes are newly formed in the period. As a result of examining the causes of the development of the lakes in terms of the inclination of topography, where glaciers are situated, it is found that the gentler an inclination of topography is, the more the glacial lakes develop.The risk of a glacial lake outburst flood (GLOF) should he evaluated by lake size, the possibility of sudden huge mass input into the lake from the lake surroundings and the extent of a moraine-dam deterioration due to cored ice melting or piping. The measures of the risk assessment were studied by means of topographic interpretation such as mass movement landform and slope failure around the lake, using optical data of ASTER and Landsat and DEM stereoscopy constructed by SAR data pair. But the relationship between these information obtained by the analysis of satellite data sod the actual risk of GLOF should be continuously studied in future, because further collection of grand truth data is still necessary to GLOF risk assessment.