Moraine derived debris supply and distribution on a Himalayan glacier

Abstract

Many glaciers throughout the Himalayas are debris covered, which substantially alters the melt processes. Though the extent of these glaciers is well studied, there is less information available of the debris thickness. This debris thickness is spatially variable, and partly caused by sediment transport processes from the slopes adjacent to the glacier. To quantify and understand these processes field data was analyzed and based on these insights a simple erosion-transport model was developed. Using UAV images and DEMs from April 2013 to May 2017, the amount of erosion and the causing processes could be distinguished. Erosion rates on the moraine are 0.25 m yr-1, which almost completely happens during the wet season. Debris flows and sediment entrainment by water flow are the processes here. The lower loose part of the moraine moves downslope with a velocity of 0.5- 1.5 m yr-1. This may be caused by solifluction or large slumping processes. Furthermore, smaller slumps and small rockfalls also contribute to the sediment transport down the moraine. The model calculates that the average debris extent outward from the moraine is approximately 30 m, covering in total 22% of the glacier surface with an average thickness of 2.2 m. This is in sharp contrast with the fact that the glacier is currently entirely covered in debris. Not all the debris is thus derived from the lateral moraines.