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 will not 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 methres,” says 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,” Shugar says.
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As the glacier flowed over the cliff and bent 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,” Shugar says. “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 the ice, producing enough liquid water to generate the huge flash floods.
“Maybe the glacier breaking is only part of the story and there’s something else that we can’t see yet,” Shugar says. “But as of now, that’s what it looks like.”
The melting of ice as a result of 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, is much larger. “These videos that we’re seeing are off the charts. This is horrific,” Shugar 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 is not the case, says at the University of Grenoble 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.”
“It starts with a high amplitude seismic signal that has the characteristics of a mass-wasting seismic signal rather than an earthquake signal,” Cook says. “Then we see a long seismic signal typical of a large debris flow that lasts for hours.”
It’s similar to what was observed during the 2021 Chamoli event, she says.
Global heating may have , 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, Shugar says, but an increase in the frequency of this kind of disaster points to global heating 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,” , head of the UN Office for Disaster Risk Reduction, . “Their lives, ways of life, culture, and heritage are all threatened.”
