How a glacier and rock collapse turned into a flash flood that engulfed a village in 30 minutes
1
Glacier and rock collapse
At an altitude of approximately 5,200m, a mass of ice and rock collapsed entirely from the Langtang Lirung slope.
2
Valley blockage
Collapse debris temporarily blocked a narrow section of the Lende Khola.
3
Formation of a temporary natural dam and lake
Water accumulated behind the blocked section, creating an impromptu natural dam — a point not previously under surveillance.
4
Natural dam collapse
The unstable debris dam could not withstand the trapped water pressure and collapsed.
5
Flash flood
The water level at the Trishuli River branch point rose by 9m in 30 minutes.
6
Amplified by debris flow
Ice, rock, and soil mixed together, striking downstream villages and power plants with much greater destructive power than a typical flood.
Between warnings and silence, the time at the Rasuwa site
08:37Collapse occurs
09:15~09:16600,000 initial text alerts sent
Around 09:20Betrawati water level gauge data lost
※ The final transmitted water level of 3.55m was below the 4.1m threshold for issuing a warning at the time. Subsequently, observation equipment in Langtang, Rasuwagadhi, Betrawati, Syabrubesi, and Malekhu were destroyed one after another by the torrent. (Source: Compiled from local reports including Online Khabar, as of Aug 28-30, 2026)