Nepal Glacier Collapse Triggered Deadly Border Floods

Satellite images reveal that a Nepal glacier collapse, triggered by a massive bedrock failure, unleashed the catastrophic flooding that killed hundreds of people along the Nepal-China border this week.

Bedrock gave way beneath the ice

Geomorphologists Kristen Cook and Dan Shugar said early images from Nepal were obscured by clouds and debris dust, showing only that part of a glacier had broken off Langtang Lirung peak near the Tibet border. Clearer images from Thursday revealed that the bedrock underneath the glacier had also collapsed, dragging a massive chunk of ice down with it and sending boulders and ice crashing into the valley.

“It shows the whole area without anything hidden, and we could see that, yes, 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 Shugar, an associate professor at the University of Calgary. “You have this big bedrock failure that took part of the glacier with it.”

Debris buried villages downstream

Shugar said it was heart-wrenching to look downstream on the images and see how debris had buried villages where people once lived. After slamming into the valley floor, the debris kept moving through the steep, narrow valley as ice melted, said Cook, of the Université Grenoble Alpes in France. Water and mud several stories high swept through communities.

Before-and-after satellite images of the Kolpurtar, Betrawati and Syapru Besi areas show the Trishuli River now much wider, and turned brown and black after overtopping its banks and filling with debris. The color change shows how much sediment the flow carried, shifting from greenish to muddy brown, Cook said. Towns along the riverbanks now appear as swaths of brown, with only a few houses still visible in images of the Betrawati area.

In Syapru Besi, a popular tourist town where a well-known trek to Langtang begins, the flooding toppled and swept away buildings. Images show a side river there is now wider too, pushed upstream by the force of the flow.

The largest glacier flood one expert has seen

The flooding “left a wasteland in its wake” that will take years to recover from, said Alton Byers, a mountain geographer at the University of Colorado at Boulder who has studied glacial hazards in Nepal for years. He called it by far the largest glacier flood he has witnessed.

Byers said he believes Wednesday’s flooding is linked to climate change, as rising global temperatures melt glaciers and permafrost, destabilizing high-altitude snow and ice and triggering cascading collapses. “All the indicators, to me, point to the impacts of warming trends,” he said. “In this case, the permafrost that for millennia has helped to hold together high-altitude rock and ice and soil and glaciers is now weakening and becoming unstable.”

Scientists urge caution on climate link

Cook and Shugar said they cannot yet confirm a direct link between the disaster and climate change. Slopes fail and landslides happen regardless, Cook said, though melting permafrost is destabilizing mountainsides more broadly.

“While we cannot at this point directly link this collapse to climate change, it is not unexpected to see more events of this type with a warming climate,” Cook said. “Not this big, hopefully not this big.”