Fast-moving ice-rock avalanche triggers deadly floods in Nepal's Himalayas
A massive ice, rock and debris avalanche descended from about 5,200 m, reaching rivers in minutes and causing floods that killed at least 900 people.
Preliminary research by Nepalese scientists indicates that an ice-rock avalanche originating near the Langtang-Lirung region fell at around 8:37 am, racing down steep slopes at an estimated 46.3 m per second. Covering about 22 km in just over seven minutes, it entered the Lhende River at roughly 2,930 m altitude and then rushed through the Bhotekoshi and Trishuli river networks, retaining enough force to cause widespread destruction despite speed reductions downstream.
Satellite data reveal major changes across a 10 km² zone and the loss of a 0.56 km² glacier segment. Analyses of satellite, hydrological and meteorological records found no evidence of a glacial lake outburst flood or unusually heavy rain on the day, challenging those earlier explanations. Water levels in upstream reaches fell hours before the surge arrived, suggesting a temporary blockage. The flood disabled 13 hydropower projects and one solar plant, removing about 431 MW of capacity, and left thousands missing while rescue teams continue searching for trapped workers.
Why it matters
Understanding the avalanche's speed and cause helps improve flood warnings and infrastructure resilience in mountainous regions.
How this story developed
- Aug 27 Flash Floods from Glacial Collapse Leave Hundreds Dead and Thousands Missing on Nepal-Tibet Border
- Aug 27 The United Nations pledged $2 million for relief efforts.
- Aug 27 The US Department of State said 90 Americans were unaccounted for in China and Nepal and it was not aware of any US deaths.
- Aug 28 Authorities warned that the debris‑clogged river and rising water in a blocked lake could cause additional flooding downstream.
- Aug 28 The Nepali army is rescuing people trapped in a tunnel at a hydropower site in Rasuwa after deadly floods.
- Aug 29 Death‑toll estimates rose to at least 579 with about 1,400 people still missing.
- Aug 30 A sudden flash flood in Bright Angel Creek at the Grand Canyon has left more than 20 people unaccounted for and prompted the evacuation of dozens of hikers and campers.
- Aug 30 Authorities have closed Phantom Ranch and the entire North Kaibab Trail pending further assessment.
- Aug 30 National disaster authorities issued new flood warnings as water levels rose in the Bhotekoshi River.
- Aug 31 International rescue teams joined Nepalese forces and fresh flood warnings were issued as river levels rose.
- Aug 31 Updated casualty figures show 734 deaths and 2,498 missing in Nepal, with 16 deaths and 546 missing in Tibet.
- Aug 31 Stage‑four water restrictions were enacted after the Transcanyon waterline was destroyed.
- Aug 31 Drilling and air‑pumping operations at the Trishuli‑3A tunnel have begun to free trapped workers.
- Aug 31 The number of missing persons in Nepal has risen to about 4,200.
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