Satellite images reveal glacier break and bedrock collapse behind Nepal floods

Rescue teams continued searching for missing people after catastrophic flooding along the Nepal-China border on Wednesday, while earth scientists examined satellite imagery to determine the event’s cause and assess the damage.

Geomorphologists Kristen Cook and Dan Shugar reported that initial images were obscured by clouds and debris, but clearer pictures taken on Thursday showed a portion of a glacier on the Langtang Lirung peak had broken off along with a large section of the underlying bedrock, sending boulders and ice down the valley.

"It looked like there was not only this glacier that had failed, but a much larger chunk of the bedrock of the mountainside itself that had given way," said Dan Shugar, associate professor at the University of Calgary.

The debris cascade continued down the steep, narrow valley, where melting ice turned into a fast-moving flow of water and mud that surged several stories high, according to Cook of the Université Grenoble Alpes. Satellite images of the Trishuli River and nearby tributaries showed the river widening dramatically and turning brown and black from the massive sediment load.

Villages along the riverbanks were buried under mud and debris, with only a few structures still visible in the Betrawati area. The flood also widened a side river near the tourist hub of Syapru Besi, where the powerful flow pushed upstream.

"The flooding left a wasteland in its wake that will take many years to recover from," said Alton Byers, mountain geographer at the University of Colorado Boulder.

Byers, who studies glacial hazards in Nepal, suggested the event is linked to climate-related warming, noting that melting permafrost reduces the stability of high-altitude rock, ice and soil. However, Cook cautioned that a direct causal link to climate change cannot yet be confirmed, though such failures may become more common in a warming climate.