What caused Nepal flood? Scientist says it was enormous landslide, glacier fall

The deadly floods that have devastated parts of Nepal can be tracked all the way to the Himalayas where a "massive geophysical event" set off a chain reaction Wednesday, a geophysicist who studies such events told ABC News.

A landslide in the mountain pass took place during the day that took away a large chunk of land with glacial ice on top in the Himalayas, Göran Ekström, at the Lamont-Doherty Earth Observatory at Columbia University told ABC News. The event was so powerful, it caused an energy equivalent of a 5.2 earthquake that was registered on seismographs around the globe.

These types of events have happened in the Himalayas before, but this was a "massive geophysical event," according to Ekström.

When rocks come down a mountain it generates a lot of energy and warms up, melting the glacier, which may be the cause as to why so much water fell on at the bottom of the mountain, according to the professor.

The ice, debris and water came down into the valley, and Ekström estimated that the flood waters were "outrageously high," possibly 130-160 feet high and that the water may have moved as fast as 44 miles per hour.

A second landslide occurred about three hours after the first, raising concerns that the first landslide left slopes unstable and that more landslides could occur in the region, Ekstrom said on Thursday.

River channels are likely blocked by mud and debris, forming dams, which could burst, according to Ekstrom.

Climate change is accelerating the melting of ice and glaciers around the globe, according to the professor.  Events like this would happen without climate change, but it is possible climate change enhances events like this, Ekström said.

"In general, these landslides in these mountainous regions are becoming more frequent, that has been determined, and that is linked to the melting of glaciers," he said.

This is not the first time the region has experienced flash flooding. On July 8, 2025, the Bhotekoshi river suddenly surged, which Nepal's Department of Hydrology and Meteorology concluded was caused by a glacial lake outburst in the Lhende river near the Nepal-China border.

Scientists warned the Himalayan region is vulnerable to this type of flooding, as it contains numerous potentially dangerous glacial lakes.

A study by the International Centre for Integrated Mountain Development and the United Nations Development Programme identified 3,624 glacial lakes across Nepal, India and Tibet, 47 of which were classified as potentially dangerous and at risk of bursting, including 21 in Nepal.

No forecast before Wednesday's flood predicted an avalanche would strike this location.

At least 358 people have been killed in the floods as of Thursday morning, according to Nepali police.

More than 1,300 people have gone missing from the affected area as of Thursday morning, according to local authorities. Of those who are out of contact, 476 are foreign tourists, according to the Nepal National Disaster Risk Reduction and Management Authority.

Of the missing, there are at least 63 American tourists, Nepal Tourism Board reported.