Multisource observations of the catastrophic 2026 ice-rock avalanche and cascading hazard in the Nepal Himalaya

On 26 August 2026, a catastrophic cascading hazard occurred on the Nepalese side of the China–Nepal border, causing widespread devastation and destroying the key China–Nepal border port. In total, more than 6,900 individuals were killed or reported missing. This event appears to represent a typical cascading process: ice–rock avalanche (IRA; travel distance >7 km) → debris flow (travel distance >13 km) → flood (travel distance >80 km), with an overall runout length exceeding 100 km. The initial ice–rock avalanche (source zone area: ~7.5 × 10⁵ m²) detached from the glacier toe of Tsangbu Ri in Nepal, with its head scarp located at 5,120 m a.s.l. The high-speed debris flow scoured valley walls up to 100–200m above the valley floor along its passage. Upon reaching Gyirong Port at a runout distance of 21.5 km, the debris flow was accompanied by a continuously decaying seismic signal intensity and gradually evolved into a flood. Multiple factors, including pre-existing bedrock fractures, progressive glacier retreat, and permafrost degradation, contributed to the initial IRA failure. Multiple analogous cascading hazards (e.g., the Sedongpu events and the 2021 Chamoli cascading hazard) have been documented across the High Himalayas in recent years, highlighting the urgent need for enhanced monitoring and early warning capabilities in this region.