Modeling Potential Glacial Lake Outburst Flood Process Chains and Effects From Artificial Lake-Level Lowering at Gepang Gath Lake, Indian Himalaya

Glacial lake outburst floods (GLOFs) are a severe threat to communities in the Himalayas; however, GLOF mitigation strategies have been implemented for only a few lakes, and future changes in hazard are rarely considered. Here, we present a comprehensive assessment of current and future GLOF hazard for Gepang Gath Lake, Western Himalaya, considering rock and/or ice avalanches cascading into the lake. We consider ground surface temperature and topography to define avalanche source zones located in areas of potentially degrading permafrost. GLOF process chains in current and future scenarios, also considering engineered lake lowering of 10 and 30 m, were evaluated. Here, varied avalanche impact waves, erosion patterns, debris flow hydraulics, and GLOF impacts at Sissu village, under 18 different scenarios were assessed. Authors demonstrated that a larger future lake does not necessarily produce larger GLOF events in Sissu, depending, among other factors, on the location from where the triggering avalanche initiates and strikes the lake. For the largest scenarios, 10 m of lowering reduces the high-intensity zone by 54% and 63% for the current and future scenarios, respectively, but has little effect on the medium-intensity flood zone. Even with 30 m of lake lowering, the Sissu helipad falls in the high-intensity zone under all moderate-to-large scenarios, with severe implications for evacuations and other emergency response actions. The approach can be extended to other glacial lakes to demonstrate the efficiency of lake lowering as an option for GLOF mitigation and enable a robust GLOF hazard and risk assessment.

Automated summary

Glacial lake outburst floods (GLOFs) pose a serious threat to Himalayan communities, but mitigation strategies are limited and future hazards are rarely considered. This study assesses the current and future GLOF hazard for Gepang Gath Lake in the Western Himalayas, considering rock and ice avalanches cascading into the lake from areas of degrading permafrost. The study evaluates different scenarios of GLOF impacts, erosion patterns, and debris flow hydraulics, taking into account the engineered lowering of the lake. The findings demonstrate that the size of the future lake does not determine the size of GLOF events in Sissu, highlighting the importance of avalanche location and impact. Lowering the lake by 10 or 30 meters can reduce the high-intensity flood zone, but the Sissu helipad remains at risk under moderate-to-large scenarios. This study provides insights into the effectiveness of lake lowering as a GLOF mitigation strategy.