What caused Nepal’s Budhi Gandaki river flood? Officials examine landslide dam and ice avalanche theories

Nepal's central Gorkha district is reeling after a surge on the Budhi Gandaki river swept away houses and bridges and damaged a hydropower project. The cause is still unknown.

Sudden river surge hits Nepal’s Gorkha district during Dashain

The flood struck on Sunday, the first day of Dashain, Nepal's biggest festival. The army says rescuers have pulled 95 people to safety along the riverbank, including nine foreigners. Five people are still missing, and no deaths had been confirmed yet.

The damage so far

Nepal's Disaster Risk Reduction and Management Authority (NDRRMA) says more than 200 homes were damaged and over 650 people were affected. The flood destroyed about a dozen houses and several suspension bridges, and it carried off construction equipment at a hydroelectric site. Some settlements are now reachable only by air, a local official told the Kathmandu Post. The army has deployed four helicopters for search and rescue.

Within a couple of hours, the river at one point rose from about two metres to nearly 8.5 metres. A government meteorologist said the hydrological station there was swept away, so no data is coming from that location.

What caused it?

Officials have not said. Two explanations are circulating:

• A landslide dam. A landslide may have blocked the river or one of its tributaries for a time. When the dammed water broke through, it would have produced a sudden surge.

• An ice avalanche. Some people upstream say they saw one.

The pulsing pattern residents described is consistent with either, but it doesn't settle the question. Experts say the flow was smaller and slower than the devastating August floods near the Tibet border.

The Budhi Gandaki has a recent precedent. A 2024 study by the International Centre for Integrated Mountain Development (ICIMOD) found that an April 2024 surge on the river was caused by an ice avalanche from the Manaslu Glacier falling into Birendra Tal, a glacial lake. The researchers warned that glacier retreat and rising temperatures could make future events larger. Nothing so far links that mechanism to Sunday's flood.

A region still recovering

The Budhi Gandaki feeds the Trishuli River, downstream of the tributary where a glacier collapse set off the August disaster. That flood killed more than 1,400 people, according to the BBC, and thousands were reported missing. Many Gorkha families are still dealing with that loss.

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