The 2024 cascading glacial lake outburst flood in the Thame Valley of Everest region, Nepal: process, impacts and implications
Abstract
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. Our analysis suggests that the moraine-covered bedrock dam of the upper lake was overtopped in response to either (1) a hydrological tipping point driven by intense glacier melt associated with extreme temperatures and precipitation, triggering a cascading failure that ultimately breached the lower lake's moraine dam, or (2) a displacement wave caused by glacier calving or a rock avalanche into the upper lake, causing dam overtopping and initiation of the cascading failure. The event released a combined water volume of approximately 7.7 × 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−1, reached Thame Village within 22 min. The socio-economic impact was severe, with losses estimated at USD 6.18 million 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.