Scientists are pointing to a glacier collapse and rock landslide as the cause of a devastating flash flood that killed at least 350 people and left many more missing near Nepal’s border with China, a mountainous region that’s increasingly imperiled by the effects of man-made climate change.
Initial assessments based on seismic and satellite data, as well as videos of the event, indicate that a very large section of a glacier detached and collapsed after the bedrock below it gave way. That in turn caused seismic waves equivalent to a 5.2 magnitude earthquake, according to the US Geological Survey. Ice from the glacier and rockfall may then have blocked the Lhende Khola river, causing water to quickly accumulate and ultimately surge downstream.
“What we’ve certainly confirmed — there was a large ice avalanche, probably a mixture of ice and rock, which detached and then became fluid and then transformed into this devastating flood,” said Simon Allen, a research associate at the University of Zurich who studies glacial hazards in the Himalayas. Allen said Thursday that early analysis of satellite images and field photos indicates the bedrock beneath the glacier failed.
Nepal is particularly vulnerable to flash floods because of its mountainous terrain and rapidly melting glaciers. Such events are becoming more frequent as global warming accelerates the ongoing thaw in the Himalayas, an area that holds more snow and ice than any place on Earth besides the Arctic and Antarctica. The development has a cascading effect — from mudslides to water scarcity — for the nearly 2 billion people living downstream from Himalayan-fed rivers, according to the United Nations.
Himalayan glaciers melted 65% faster between 2010 and 2020 than during the previous decade, the UN said, while the risk of glacial lake-related flooding across the broader Hindu Kush Himalaya region is expected to roughly triple by the end of the century.
“When you put together all the physical understanding that the glaciers are retreating, permafrost is thawing, it certainly adds up,” said the University of Zurich’s Allen. Experts are concluding “that we are seeing and we are expecting these events to become more frequent,” he said.
While a definitive cause of the Aug. 26 floods has yet to be established, analysis so far indicates the snout of a glacier at an elevation of roughly 5,200 meters broke away and began to make a steep descent to the valley floor, melting ice and gathering sediment as it did so, said Dan Shugar, a geomorphologist and an associate professor at the University of Calgary. The mountains have been shrouded in clouds, meaning the precise chain of events is likely to be better understood once satellites can do a clearer examination.
“When you have a lot of rock falling a great distance it generates a lot of heat and that can melt a lot of ice, so that could explain part of the water that we see in the absolutely horrific videos,” Shugar said.
“At the moment we’ve got the hydrology data, have some seismology data, we’ve got some remote sensing data, we have the videos,” he said. “We don’t yet have eye-witness accounts from right in the valley, or a helicopter flyover of the source area.”
