Abstract
Cascading hazards in high-mountain environments can evolve rapidly from slope failure to destructive downstream flooding, challenging conventional early-warning systems. The 26 August 2026 Langtang Lirung rock–ice avalanche and subsequent flood cascade along the Bhote Koshi–Trishuli corridor were examined through a retrospective synthesis of seismic, terrain, hydrological and documentary evidence. Event chronology reconstruc-tion and reach-based analysis yielded apparent celerities of 47.3, 20.9 and 6.0 m s−1 across successive reaches of 22, 44 and 130 km. Propagation over the approximately 196 km cor-ridor occurred within 6 h 43 min of the catalogued seismic marker. Deterministic sensitiv-ity analysis preserved the downstream decline in celerity under the specified timing and distance perturbations, although uncertainty in event initiation, flow formation and ob-servational timing limits hydraulic interpretation. The warning-chain assessment identi-fied insufficient evidence to verify end-to-end operational capability. A two-stage frame-work is proposed, which combines evidence-based hazard screening, operational readi-ness, scenario development and direct emergency escalation.
