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Before-and-after satellite images show a glacier shrinking and a river swelling.
The floodwaters that killed more than 300 people in Nepal and China on Thursday were probably unleashed by a landslide from a collapsing glacier, according to a rapid analysis by a team of geoscientists – a harbinger of the
dangers posed by melting ice in a warming world.
High-resolution images taken by satellite monitoring company Planet Labs show the site of the apparent landslide high in the Himalayas, close to the Nepal-China border. In the “before” image, a glacier can be seen looming some 4000 feet (1219 metres) above a narrow valley, emptying into the meandering Lhende River.
Afterward, the glacier appears smaller by about 2 million square feet – equal to the area of about 25 professional soccer fields. The valley is strewn with ice and mud. And the river is swollen beyond its banks, submerging the surrounding vegetation beneath murky brown floodwaters.
“You can imagine this big mass of ice sat high up with lots of potential energy, and as it breaks off and … hits the bottom of the valley, all that ice is getting pulverised into smaller chunks and a huge amount of water,” said Simon Cook, a University of Dundee glaciologist who was part of the team that analysed the Planet Labs images.
The tremors from the cataclysm were powerful enough that it was initially mistaken for an earthquake, though the US Geological Survey ultimately concluded that the 5.2-magnitude seismic event was caused by a “glacial collapse and debris flow”.
Nepal’s disaster management agency also attributed the floods to a “rock and ice avalanche” in a post on X on Thursday.
The flooding in Nepal killed at least 270 people, Nepal police said on Friday, and hundreds remain unaccounted for, according to the disaster management agency. More than 600 tourists are among the missing, according to the Nepal Tourism Board. Chinese state media said there were at least three deaths and 558 people missing in Tibet.
CCTV footage showed a tsunami of water, rock and ice surging through a busy border crossing, swallowing up people and a multi-storey building. The torrent probably arrived at the crossing point about 10 minutes after the initial avalanche, Cook said, which would have given people little time to flee even if an early-warning system had been in place.
Although it will take further research to discern the precise cause of this incident, collapsing mountain glaciers are a worsening symptom of global climate change, Cook said. Rising temperatures have thawed permafrost and accelerated melt, making high-altitude ice dangerously unstable.
In the past five years alone, glacier collapses have buried a Swiss village, killed 11 mountaineers in Italy and triggered floods that destroyed two hydropower plants and swept away at least 200 people in India.
But with some 200,000 glaciers clinging to mountainsides around the world – and most of them shrinking at an unprecedented rate – there is no easy way to determine which will lead to the next disaster.
“We just don’t know exactly what the cause is in some of these cases, and if you don’t know what the cause is, it makes it hard to monitor, because you don’t know what to look for,” Cook said. “It’s a real devilish problem, I’m afraid.”
It’s still not exactly clear what triggered Thursday’s incident, which involved a remote glacier known to scientists as RGI2000-v7.0-G-15-05732, Cook said.
