The catastrophic flood that killed hundreds of people in Nepal on Aug. 26, 2026, and left many more missing likely began with falling ice and rock crashing into the river below, but that wasn’t the end of the disaster. Days later, a new lake pooled behind the debris and then burst, sending more water streaming through the valley.

The destruction represents two of the ways rising temperatures, thawing permafrost and melting ice are increasing the risk of destructive floods in the Himalayas and other high mountain regions around the world.

I am a geologist and part of an ad hoc international group of 50-plus scientists who meet quickly after mountain disasters to analyze satellite images and field data to get information out to the public. This is what we’ve learned so far about the disaster and the region’s rising risks from climate change.

The flood disaster in Nepal

Evidence from satellites and seismic data we have reviewed suggest that an enormous mass of bedrock and glacier ice broke off a slope north of Langtang Lirung and slammed into the valley about 4,000 feet (1,200 meters) below – that’s a distance roughly three times the height of the Eiffel Tower. The landslide shook the earth hard enough to register as a magnitude 5.2 event on seismometers, the U.S. Geological Survey confirmed.

The result was a slurry of melting ice, rock and water that quickly flowed into the river.

We have a rough idea of how much ice fell, and it likely wouldn’t have been enough to trigger the magnitude of the flood that followed. One theory is that the rock and ice briefly dammed the valley, allowing water to back up in the river.

When that blockage broke, a wall of water rushed downstream – reaching towns, taking hundreds of lives and destroying infrastructure. Hundreds more people were stranded by the flood.

Second threat: The lake that formed, then burst

The disaster wasn’t finished when the first wall of water passed. Within a day, authorities warned that a new “barrier lake” estimated to hold a few million cubic meters of water had developed behind avalanche and flood debris where two........

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