A collapsed glacier on the Nepal-Tibet border triggered a flash flood that has killed at least 469 people, with more than 1,000 others missing. The flood swept through populated valleys after part of a glacier collapsed into the valley below.
Initial reports suggested an earthquake had caused a landslide, which then caused the flood. The US Geological Survey (USGS) later said the disaster was caused by a “glacial collapse”, when a glacier or part of a glacier disintegrates.
The impact of the collapsed glacier hitting the bottom of the valley registered a magnitude of 5.2, according to USGS data and scientists. Dr Simon Cook, from the University of Dundee's team, detected that the lower part of a glacier in Nepal near the Langtang Lirung peak had collapsed.
Jakob Steiner, a geoscientist, said a 1,300-metre-wide chunk had been cut from the lower part of a glacier in Nepal's Himalayas. Rivers downstream rose by between seven and nine metres within a span of 30 minutes.
Satellite imagery appeared to show significant snow loss in the valley during the 24 hours before the disaster. Scientists are still investigating the precise mechanisms that destabilised the site.
The collapse follows a glacial flash flood in the same region the previous year. Dr Cook said such catastrophic disasters were happening “at a regular basis”.
The Himalayan region is warming about twice as quickly as the global average. Rising temperatures are causing glaciers to retreat and mountain permafrost to thaw, weakening the stability of slopes.
Permafrost can act like glue, holding fractured rock and adjacent ice together on steep mountain slopes. As it thaws, the structure of a mountainside can become less stable.
An analysis released by ICIMOD earlier this year found that Hindu Kush Himalaya glaciers are now losing ice at double the rate since 2000. Nepal's mountains have lost close to one-third of their ice in slightly more than three decades.
Glaciers across the Hindu Kush Himalayas disappeared 65% faster between 2011 and 2020 than during the previous decade. Alton Byers, a mountain geographer at the University of Colorado, Boulder, said: “These catastrophic floods are becoming more frequent”.
Scientists said climate change should not be presented as the sole or confirmed immediate cause of this collapse. Events on this scale have been documented too rarely for researchers to establish a clear statistical relationship between individual glacier collapses and global warming.
John Pomeroy, director of the University of Saskatchewan's Centre for Hydrology, said: “will get events like this every year, somewhere in the world”.
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