The 2024 cascading glacial lake outburst flood in the Thame Valley of Everest region, Nepal: process, impacts and implications

Abstract. On the afternoon of 16 August 2024, a catastrophic flood devastated Thame Village in the Everest region of Nepal. This event resulted from a cascading glacial lake outburst flood (GLOF), where the outburst of an upstream glacial lake triggered the failure of a downstream lake in the headwaters—a complex hazard chain often-overlooked in conventional risk assessments. By integrating multi-source satellite imagery, field data, climatic data, empirical estimations, and numerical modelling, we analyse the triggers, processes, and consequences of the cascading failure. We find that the upper lake, which formed in the late 2000s, expanded rapidly to 0.11 km² prior to its outburst, while the lower lake grew by 20 % between 1989 and 2024. The hydrological tipping point for the upper lake was driven by intense glacier melt and calving from extreme temperatures and precipitation. Its overtopping triggered a cascade, causing the breach of the lower lake’s moraine dam and releasing a combined water volume of approximately 6 (± 0.65) ×10⁵ m³. Multi-phase mass flow modelling reconstructing two possible scenarios indicates that the flood wave, with an initial peak discharge exceeding 800 m³/s, reached Thame Village within 22 to 32 minutes. The socio-economic impact was severe, with losses estimated at 6.18 million USD within the Khumbu Pasang Lhamu Rural Municipality alone, and flood effects traced over 50 km downstream. This event demonstrates that small, rapidly evolving glacial lakes, conditioned by climate-induced glacier retreat, can generate devastatingly powerful GLOFs. This underscores a critical need to broaden GLOF risk assessments to include such small lakes and to prioritize reducing exposure and vulnerability in dynamic high-mountain communities over solely engineering-based hazard control.