Glacial Lake Outburst Flood (GLOF) hazard risk assessment of Gepang Gath glacier located in Spiti Basin, western Himalaya, India

The effects of recent climate change have been sensitively pronounced on the glacier resources of the Himalaya. Therefore, the formation of moraine dammed glacial lakes leading to outburst floods is a major concern. In the present GLOF risk assessment involving the analysis of temporal changes in Lake Area, Lake Outburst probability, potential outburst magnitudes and associated damage has been evaluated. Gepang Gath glacier, which is main water head of Sissu River, has an area of 10.81 km2, the snout of the glacier calves directly in the pro-glacial lake. The present study is based on the field surveys, and Satellite data (such as MSS, TM, ETM, CORONA, and ASTER). The field surveys were carried out during summer season of 2008, 2012, 2013 and 2014 and the lake was mapped by Total Station. The combined study of field data and satellite data shows that the Gepang Gath has receded 888.15 m from 1971, at an average rate of 21.14 m/year, resulting in the formation of huge pro-glacial lake. During our study, it was observed that the lake area has progressively increased from 0.144 km2 in 1971 to 0.81 km2 in 2013 at an average rate of 0.01585 km2 per annum. But the rate of retreat and rate of the lake area expansion have increased manifolds in the last one decade; the glacier receded at the rate of 44.98 m/year from 2003-2013 and its pro-glacial lake has expanded at the rate of 0.050 km2 per annum in the same time period. The lake outburst probability shows a very high value of 42%, with a peak discharge of 1628 m3/s.