The devastating flash flood that ripped through the border communities of Nepal and Tibet has heightened fears that the climate crisis is destabilising the geology of mountain and polar regions, threatening millions of people. Satellite imagery suggests a glacier collapse high in the Himalayas was the primary cause of the deadly torrent of mud, water and ice that tore along the Bhotekoshi River on Wednesday. It swept away buildings and roads and left at least 360 dead and 1,400 missing.
A magnitude 4.4 earthquake was initially blamed for the collapse. However, it is now thought to have been caused by the huge wall of ice that crashed down on to the north slope of Langtang Lirung, a 7,ooo-metre (23,000ft) mountain, the impact of which registered a magnitude of 5.2. The ice-rock avalanche pushed boulders and other debris into the Lhende Khola River, a tributary of the Bhotekoshi River.
Water levels in rivers downstream rose by between 7 and 9 metres within 30 minutes, according to the International Centre for Integrated Mountain Development, an intergovernmental scientific institution. Scientists are still examining the precise mechanics of the Himalayan disaster, but many observe that glaciers and permafrost around the world are being weakened by global heating, caused by the burning of gas, oil and coal. The detachment of a chunk of the glacier wall came amid unusual heat that was likely to have melted the ice that bound the splintered bedrock together.
Two days before the collapse, the ground temperature hit its highest point in the last two years, according to Dr Hamish Pritchard, a glaciologist with the British Antarctic Survey, whose team had sensors 6 miles (10km) away from the site. A series of intense heatwaves has hit the region since early this year and has affected countries around the world. Another factor here was the monsoon season, which saturated the soil and swelled rivers.
Disasters like this were foretold. In 2023 the UN’s top scientific advisory body warned that previously ice-bound landmasses – from permafrost tundra to mountain glaciers – would become increasingly unstable as temperatures rose. Even faster warming is occurring in alpine and polar regions because the loss of snow and ice is removing the thermal insulation of the land.
Dr Richard Waller, a senior lecturer in physical geography at Keele University, said: “The progressive loss of snow and glacier ice results in the surface being less reflective, so it absorbs more solar energy and heats up. In combination with atmospheric warming, this is leading to the melting of mountain permafrost. As the permafrost and the ice-filled joints melt, then there’s the potential for these types of catastrophic failure.” The thaw is altering the shape, colour and solidity of the landscape, creating or expanding glacial meltwater lakes and, in the long term, threatening the origin of many rivers and the drinking supplies of populations downstream.
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