The Himalayan Hazard: Post-Event Assessment of Thame Glacial Lake Outburst Flood in Everest Region, Nepal

Abstract

Glacial Lake Outburst Floods (GLOFs) represent one of the most significant geomorphic hazards in the Hindu Kush Himalaya (HKH), where rapid glacier retreat, unstable moraine-dammed lakes, and steep mountain topography create high downstream risk. On 16 August 2024, a cascading GLOF occurred in Thame Valley, Solukhumbu District, Nepal, following a rock avalanche into Upper Ngole-Cho Lake. The displaced lake water overtopped into Lower Ngole-Cho, causing moraine dam failure and releasing approximately 0.5 million m³ of water and sediment. The resulting debris-laden flood travelled through Thame Khola, severely damaging Thame Village, hydropower infrastructure, agricultural land, and transportation routes. This study presents a post-event geomorphic and geotechnical assessment conducted between November and December 2024. Field investigations revealed extensive channel incision, lateral bank erosion, sediment deposition, and widespread slope instability. Deep-seated retrogressive landslides developed within weak glacio-lacustrine deposits underlying Thame Village and continue to evolve during rainfall events. The study highlights the importance of valley morphology, sediment characteristics, and cascading geomorphic processes in amplifying GLOF impacts. Results emphasize that post-GLOF hazards may persist long after the flood event and require sustained monitoring and mitigation.