Challenges in predicting glacial lake outburst floods and suggested pathways forward

Ongoing rapid atmospheric warming is driving accelerated melting and retreat of mountain glaciers worldwide. Consequently, there has been a rapid expansion of glacial lakes. Sudden failures of the natural dams of these glacial lakes can generate glacial lake outburst floods (GLOFs), caused by both internal conditioning factors and external triggers. Some of these GLOFs have been catastrophic1 due to steep elevation gradients and the presence of abundant sediment transport in mountain rivers. GLOFs produce powerful flows that cause substantial damage to infrastructure, including roads, bridges, hydropower stations, and settlements, and result in loss of life.

Geoscientists worldwide have conducted extensive research on glacial lake mapping, field surveys, and the identification of GLOF mechanisms and triggers.3 These datasets and the associated knowledge enrich risk assessments and projections.4 Early warning systems (EWSs) have been established in some at-risk valleys, yet effective and timely warnings remain rare. For instance, the China-Nepal transboundary GLOF that occurred on July 8, 2025, in Jilong County, Xizang, China, caused around 29 fatalities and widespread infrastructure damage. This recent event, which originated from a small, overlooked supraglacial lake, illustrates persistent challenges in GLOF risk assessment and underscores the need to rethink the limits of EWS prediction.

Complex triggers and conditioning factors

GLOF risk assessment is challenging due to highly complex triggers, mechanisms, and flow characteristics. Lake type strongly influences response to external disturbances: supraglacial lakes can form or drain episodically through subglacial conduits; ice-dammed lakes are prone to sudden drainage triggered by dam thinning or flotation; and moraine-dammed lakes are vulnerable to ice avalanches, landslides, extreme rainfall, permafrost thaw, or piping that weakens the dam to sudden failure through compound events. This diversity of lake types generates multiple interacting processes, increasing uncertainty in predicting outbursts (Figure 1). Even minor disturbances can evolve into catastrophic floods under specific conditions.