A glacier collapse is most likely cause of the Nepal disaster
Melting snow appears to have weakened a steep glacier at an altitude of 5 kilometres, causing it to plummet around a kilometre into the river valley below
The full extent of the deaths and damage caused by the enormous flash flood that swept down a river valley in Nepal and Tibet today won’t be clear for weeks. But initial analyses of satellite images and seismic data suggest that the collapse of a high glacier caused the disaster.
“There’s a glacier that rolls over a cliff at about 5200 metres,” says Dan Shugar at the University of Calgary in Canada. “It’s just like a perfect straight line where it snapped off and dropped over a kilometre vertically to the valley bottom.”
This collapse could be a result of global heating. “It’s not that much of a stretch to think, yes, we’re seeing one terrible ramification of human-caused climate change,” he says.
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As the glacier flowed over the cliff and moved down the steep slope, deep crevasses would have formed in the ice. Warm weather in the past day or so may have melted a lot of snow and some glacier ice, with this liquid water weakening the glacier and causing the entire section flowing down the steep slope to collapse.
“Comparing satellite imagery from yesterday and today, the glaciers in the vicinity do seem to have lost a fair bit of snow in the last 24 hours,” says Shugar. “My guess is that snow melt, and glacier ice melt as well, injected a lot of liquid water into the glacier, which percolated down to the bed and lubricated it. That was enough for it to collapse.”
The potential energy released as heat when millions of tonnes of ice fell a kilometre may have melted large quantities of it, producing enough liquid water to generate the huge flash flood.
“Maybe the glacier breaking is only part of the story and there’s something else that we can’t see yet,” says Shugar. “But as of now, that’s what it looks like.”
The melting of ice due to the release of potential energy caused the Chamoli flash flood in India in February 2021. “In that case, it was a large landslide but with a bit of glacier ice on top of it,” says Shugar. “When that much ice falls, there’s a lot of heat generated and it can melt.”
This event, however, was much larger. “These videos that we’re seeing are off the charts. This is horrific,” he says. “It looks like this will rank very high on the list of historic mountain disasters in terms of people killed, and cost.”
Some reports have suggested that an earthquake triggered the event, but this isn’t the case, says Kristen Cook at the University of Grenoble Alpes in France. “I have looked at the data from a few stations in the region, including a station from the Nepali national seismic network near Kathmandu, and we see the event very clearly in this record.”
The record begins with a strong signal of a form typically associated with the mass movement of material, rather than with an earthquake, says Cook. “Then we see a long seismic signal typical of a large debris flow that lasts for hours.”
It is similar to what was observed during the 2021 Chamoli event, she says.
Global heating may have contributed to the Chamoli event and to the collapse of a glacier above the village of Blatten in Switzerland in 2025. Steep glaciers can break for reasons unrelated to climate change, says Shugar, but an increase in the frequency of this kind of disaster points to warming as a contributing factor.
“Mountain communities around the world, from the Alps to the Andes and the Himalayas, are threatened by increasing intensity and frequency of mountain-related hazards,” said Kamal Kishore, head of the United Nations Office for Disaster Risk Reduction, in a statement after the Blatten disaster. “Their lives, ways of life, culture, and heritage are all threatened.”
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