Recent changes in the snout position and surface velocity of Gangotri glacier observed from space

Glacier mass variations have a direct impact on some of the key components of the global water cycle, including sea level rise and freshwater availability. Apart from being one of the largest Himalayan glaciers, Gangotri is one of the sources of water for the Ganges river, which has a considerable influence on the socioeconomic structure of a largely over-populated catchment area accounting for approximate to 26% of India's landmass. In this study, we present the most recent assessment of the Gangotri glacier dynamics, combining the use of interferometric techniques on synthetic aperture radar data and sub-pixel offset tracking on Advanced Spaceborne Thermal Emission and Reflection Radiometer (ASTER) satellite imagery. Results show that on average, the Gangotri glacier snout has receded at a rate of 21.3 +/- 3m year(-1) over a period of 6 years (2004-2010). While glacier surface velocity near the snout is estimated to be between 24.8 +/- 2.3 and 28.9 +/- 2.3m year(-1), interior portions of the glacier recorded velocities in the range of 13.9 +/- 2.3 to 70.2 +/- 2.3m year(-1). Further, the average glacier surface velocity in the northern (lower) portions (28.1 +/- 2.3 m year(-1)) is observed to be significantly lower than in the southern (higher) portions (48.1 +/- 2.3m year(-1)) of the Gangotri glacier. These values are calculated with an uncertainty of less than 5 m year(-1). Results also highlight a consistent retreat and non-uniform dynamics of the Gangotri glacier.