Quantifying Changes in the Gangotri Glacier of Central Himalaya: Evidence for Increasing Mass Loss and Decreasing Velocity

The status of Gangotri, one of the largest Himalayan glaciers, has been a matter of scientific debate and close scrutiny of the global hydrologic community. To comprehend the current state of Gangotri Glacier, we estimated it's geodetic mass budget and ice velocity using optical satellite data. The spatial distribution of ice thickness, using a laminar flow equation, and possible locations of glacial lake formation are also analyzed. The geodetic mass budget of Gangotri Glacier, estimated for the period of 1999-2014, yielded a value of -0.55 +/- 0.42 mw.e.a(-1). Substantial decrease in ice velocity is also noted for a nearly contemporaneous period. The average decrease in velocity for the 14 year (1999-2000 to 2013-14) observation period is computed to be 6.98 +/- 6.53 ma(-1). While the deceleration is less pronounced in the accumulation areas and along the tributaries, palpable slowdown (11.07 +/- 6.53 ma(-1)) is observed along the main trunk of the glacier. The ice velocity maps produced are further used for computing glacier ice thickness and bedrock topography. Depressions in the bedrock topography are identified as potential sites for the formation of supraglacial lakes, as and when the snout retreats. In total, eight bed overdeepenings, with a maximum volume of 56.57 +/- 8.93 x 10(6) m(3), have been identified and demarcated as potential sites for lake formation. The results presented here highlight increasing mass loss and reducing velocity patterns of the Gangotri Glacier.