The size and volume of the ice, the precise trigger for the avalanche, and the source of the floodwater remain to be determined, glaciologists who have been assessing the risk of floods from glaciers in the Himalayan region said.

A preliminary analysis based on satellite imagery suggests that an ice-rock avalanche led to a temporary river blockage, followed by "a sudden release of impounded water and debris", the National Remote Sensing Centre, Hyderabad, said.

The International Centre for Integrated Mountain Development (ICIMOD), an intergovernmental agency in Nepal, said the ice and rock debris had entered Lende Khola, a tributary of the Bhote Koshi river, generating a surge carrying water, sediment and large boulders downstream.

Water levels rose by nine metres at some sites within 30 minutes, the ICIMOD said.

"This was an extraordinary event - but we need to understand the mechanism and the source of the floodwater," said Ashim Sattar, glaciologist and assistant professor at the School of Earth, Ocean and Climate Sciences at IIT Bhubaneswar.

"It's possible that the avalanche triggered processes similar to what happened in Chamoli in 2021," Sattar said.

Sattar had been a member of a study team that estimated that 27 million cubic metres of rock and ice - enough to fill 10,800 Olympic-size swimming pools - had collapsed upstream of Chamoli.

The rock and ice avalanche turned into a large debris flow that hurtled down the valleys towards Chamoli.

Wednesday's event had initially been linked to a 4.4-magnitude earthquake. But the US Geological Service said additional analyses of seismic data and satellite images indicated that a glacial collapse and debris flow had led to a 5.2-magnitude seismic event.

The trigger for the ice-rock avalanche remains unclear, said Reet Tiwari, a remote sensing specialist with the civil engineering department at IIT Ropar.

"Loosening of melting ice or even exceptional rainfall could shift the centre of gravity of a large ice mass and create an instability," Tiwari said.

He said detailed analyses of satellite imagery before and after the event would help scientists estimate the volume of the ice that broke away. This would determine how much water was suddenly injected into the tributaries or valleys downstream.

University of Calgary scientist Daniel Shugar said the width of the glacier failure could range between 2km and 2.5 km.

"It was a big failure and was most likely bedrock rather than glacier ice -- possibly a very large rock avalanche that took part of the glacier with it," Shugar told The Telegraph.

A UN expert, Dipesh Chapagain, told this newspaper that an impact on India could not be ruled out as flash floods are known to affect areas 100km downstream. "Cascading effects" might follow, he warned.

Chapagain, a senior research associate in the Global Mountain Safeguard Research programme at the United Nations University Institute for Environment and Human Security, said the link between seismic activity and avalanches was not yet clear.

A woman cries as she waits for updates on whereabouts of her missing family member, in the aftermath of flash floods, outside the Maithali Barrack, an army training center which serves as a primary base to airlift survivors from Rasuwa at Trishuli in Nuwakot district, Nepal, August 27, 2026. Reuters

Speaking from Bonn, Germany, Chapagain said a major part of an unnamed evolving glacier on the Nepal side of the Himalayas had collapsed, melting ice which blocked the river for some time and triggered the flood.

"Rising temperatures have long been contributing to glacial lake outburst floods (GLOFs), the abrupt release of water from glacial lakes," he said.

A study that analysed 500 GLOFs has shown that the rate of such incidents has increased fivefold since 1950, Chapagain said.

He added that GLOFs can have cascading effects -- another glacial lake is expanding on the Nepal-China border and could burst and trigger another flood.

"Though the event would be far from India, such incidents can impact up to 100km downstream. Impacts on India cannot be ruled out," Chapagain said.