Structural Controls on Himalayan Glacial Lake Expansion

As glaciers in the Himalaya have lost mass, their proglacial lakes have expanded. Despite increasing interest in hazard assessment and mitigation of Glacial Lake Outburst Floods (GLOFs) over more than the last two decades, the role of glacier structures in controlling patterns and rates of glacier recession, and subsequently of lake expansion, have not yet been investigated in detail. This study aims to identify and map glacier structures over a 20-year period and investigate their significance in ice front recession. Four glacial lakes and their associated debris-covered glaciers have been examined in the Everest Region of Nepal and China: Imja Tsho, Tsho Rolpa, Lumdin Tsho, and Dang Pu Tsho. Lake area was mapped between 2000 and 2020 using images acquired from Landsat 5/7/8 and Sentinel 2. Discrete glacier flow units were identified and specific structures were digitised using the finest-resolution panchromatic bands. We reveal a distinct pattern of transverse features across each glacier that can be related to ice frontal position through time. While this is not the only controlling factor contributing towards ice front recession from lake-terminating glaciers in the Himalaya, it is clear that pre-existing structures influence the ice front shape and are involved in ice front deterioration. These observations could be used to indicate future ice front positions and behaviour, and rates of glacier recession and of lake expansion.  This would also enable GLOF hazard assessments to include more detailed glaciological factors and help in the recognition of such legacy structures in the behaviour of stagnant debris-covered ice masses that are part of terminal moraine complexes.