Identification of potential glacial lake sites and mapping maximum extent of existing glacier lakes in Drang Drung and Samudra Tapu glaciers, Indian Himalaya

The Himalayan glaciers feed major Asian river systems sustaining the lives of more than 800 million people. Though the rates of retreat of individual glaciers are uncertain, on the whole the Himalayan glaciers have been losing mass at an increasing rate over the past few decades. With the changing climate, glaciers will continue to shrink and the rates of retreat may increase even further. This may lead to the formation of moraine dammed glacial lakes, which can cause outburst floods upon failure of the dam, catastrophic to human life and infrastructure downstream. Therefore, identification of potential lake sites and predicting the expansion of existing lakes are crucial for timely monitoring and mitigation of these hazards. In the present study, glacier surface velocity and slope are used to calculate ice thickness, by applying a basic parallel flow model, subsequently outlining the bed topography and locating potential lake sites in over-deepenings in the bedrock. Comparison of the modelled and measured ice thickness values on Chhota Shigri glacier suggests a model uncertainty of +/- 15%. The model is further applied to Samudra Tapu and Drang Drung glaciers using satellite data between the years 1999 and 2001, where eight potential lake sites were identified with mean depths varying between 33 +/- 5 and 93 +/- 14 m, of which three sites have a volume greater than 0.01 km(3). The analysis predicts an over-deepening near the snout of Samudra Tapu, in close proximity to an existing moraine dammed lake. A portion of the predicted site has already evolved into a lake between the years 2000 and 2015, which upon further deglaciation could lead to an expansion of the existing lake by an area of 14 +/- 2 ha. This observation further validates the model prediction of lake expansion. The present study demonstrates the utility of the model to predict maximum expansion of the existing lakes and possible formation of new lakes due to glacier retreat. Systematic application of this technique can provide information crucial to policy makers and planners dealing with the security of people living in the mountains.