Scientists are still piecing together information from satellite and ground-level data to figure out exactly what happened to cause the flood, which killed at least 350 people and left more than 1,300 missing, including more than 60 Americans.
The U.S. Geological Survey on Wednesday reported a magnitude 5.2 glacier collapse that sent debris flowing downstream with catastrophic impact on communities. It said its determination was based on data from nearby seismic stations, long period seismic waves and satellite imagery.
“A lower part of a glacier has really come off,” said Jakob Steiner, a geoscientist at the University of Graz in Austria who is currently based in Bangladesh. “If you look at the imagery it’s like someone cut with a huge knife through the whole lower part and it fell off.”
Steiner said a mass of glacial ice dropping from a great height could have felt like a bomb exploding, resulting in the chaos that followed.
Hundreds have lost their homes across the Himalayan region, and officials reported large-scale damage to critical infrastructure, including hydropower dams, roads, buildings and bridges in the region.
Sudden rise in water levels gave no chance to escape
Water levels in rivers across the flood-affected region rose by as much as 29.5 feet in 30 minutes as a result of the surge from the glacial detachment upstream, researchers at the Kathmandu-based climate research group said.
“It was a huge rise, a huge surge of water that happened suddenly,” said Sanyal.
Preliminary evidence suggests a large volume of ice and rock may have plunged into the Lhende Khola, a tributary of the Bhote Koshi River. Researchers said the collapse could have displaced water and picked up loose sediment and boulders, producing a powerful surge downstream. Researchers are also examining whether debris temporarily dammed the river before the impounded water burst through, magnifying the flood.
Steiner said the area has a history of destructive mountain hazards. Floods originating from a glacial lake struck the same valley in 2025, while an ice and rock avalanche occurred elsewhere in the area in 2024. The broader Langtang region was also hit by devastating avalanches during Nepal’s 2015 earthquake.
