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鈥檛 be clear for weeks. But initial analyses of satellite images and seismic data suggest that the collapse of a high glacier caused the disaster.
鈥淭here鈥檚 a glacier that rolls over a cliff at about 5200 metres,鈥� says at the University of Calgary in Canada. 鈥淚t鈥檚 just like a perfect straight line where it snapped off and dropped over a kilometre vertically to the valley bottom.鈥�
This collapse could be a result of global heating. 鈥淚t鈥檚 not that much of a stretch to think, yes, we鈥檙e seeing one terrible ramification of human-caused climate change,鈥� 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.
鈥淐omparing 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,鈥� says Shugar. 鈥淢y 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.鈥�
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.
鈥淢aybe the glacier breaking is only part of the story and there鈥檚 something else that we can鈥檛 see yet,鈥� says Shugar. 鈥淏ut as of now, that鈥檚 what it looks like.鈥�
The melting of ice due to the release of potential energy caused the Chamoli flash flood in India in February 2021. 鈥淚n that case, it was a large landslide but with a bit of glacier ice on top of it,鈥� says Shugar. 鈥淲hen that much ice falls, there鈥檚 a lot of heat generated and it can melt.鈥�
This event, however, was much larger. 鈥淭hese videos that we鈥檙e seeing are off the charts. This is horrific,鈥� he says. 鈥淚t looks like this will rank very high on the list of historic mountain disasters in terms of people killed, and cost.鈥�
Some reports have suggested that an earthquake triggered the event, but this isn鈥檛 the case, says at the University of Grenoble Alpes in France. 鈥淚 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.鈥�
鈥淚t starts with a high-amplitude seismic signal that has the characteristics of a mass-wasting seismic signal rather than an earthquake signal,鈥� says Cook. 鈥淭hen we see a long seismic signal typical of a large debris flow that lasts for hours.鈥�
It is 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, says Shugar, but an increase in the frequency of this kind of disaster points to warming as a contributing factor.
鈥淢ountain communities around the world, from the Alps to the Andes and the Himalayas, are threatened by increasing intensity and frequency of mountain-related hazards,鈥� said , head of the United Nations Office for Disaster Risk Reduction,. 鈥淭heir lives, ways of life, culture, and heritage are all threatened.鈥�
