A deadly flash flood near Nepal’s border with China may have been triggered when the lower section of a glacier collapsed and plunged hundreds of meters onto the valley floor, experts said after reviewing satellite imagery.
The cause of the glacier collapse was not immediately clear. Nepali officials said an earthquake reported in the region minutes before the flooding was one possible factor.
Before-and-after images from Planet Labs showed a lush green mountainside transformed into a landscape covered with brown debris and sediment.
Vikram Gupta, an engineering geology specialist and professor at India’s Sikkim University, said the satellite images confirmed that a significant portion of the glacier’s snout had collapsed.
“It’s confirmed that a substantial portion of that glacier snout collapsed to initiate the event — probably including or entraining a fair amount of rock and sediment,” Gupta said.
Dan Shugar, an earth scientist and associate professor at the University of Calgary, said the images also appeared to show rapid snowmelt in the 24 hours before the disaster.
“Some of the glaciers in the valley were covered in snow yesterday and today they are mostly bare ice,” Shugar said. “So in other words — and I haven’t seen any weather station data yet — it was probably warm.”
Shugar said satellite imagery taken the morning after the flood appeared to show that the lower part of a glacier broke away at an elevation of about 5,200 meters (17,060 feet) and crashed roughly 1,200 meters (3,940 feet) below onto the valley floor.
Nepal’s National Disaster Risk Reduction and Management Authority said the “glacier-inclusive flood” occurred in the Lhende River after a landslide about 20 kilometers (12 miles) northeast of a Nepal-China border crossing.
