Estimating the Bedrock Topography of the Gangotri Glacier in India

Abstract:

Himalayan glaciers make useful contribution in the runoff of many rivers in South Asia. Knowledge of depth and bottom topography is useful in understanding future distribution of glaciers; the evolution of periglacial morphology and the subglacial drainage pattern. In this investigation, we have estimated the bedrock topography of Gangotri glacier which is located in the Indian part of Central Himalayas. The Gangotri glacier is one of the largest glaciers and has an areal extent of around 140 Km².It is considered traditionally to be the source of River Ganges which is one of the main source of water for a large population living in the Indo-Gangetic plains. The bottom topography was estimated using the ice thickness and surface elevation. Ice thickness was estimated using an ice flow model, surface velocities and slope. Surface velocities were estimated using sub-pixel correlation of Landsat TM and ETM+ imagery for the years 2009 and 2010. The velocities that were estimated ranged from 14-85 m/a in the upper reaches to 20-30 m/a near the snout. The surface elevation was estimated using ASTER DEM and varied from ~4100 m near the snout to ~6600 m in the upper reaches. The combination of surface elevation and depth was used to estimate spatial distribution of bottom topography. The estimated bottom topography varies from ~3900 to 6100 masl and also shows number of depressions as deep as 50-100m. These depressions are potential sites for the formation of periglacial lakes, influencing future retreat and security of the region.