Unusual heat this year may have melted ice and thawed bonds that hold glaciers in place – leading to catastrophe
Nepal-Tibet flash flood – latest updates
What caused the flash flood in Nepal and Tibet?
The devastating flash flood that has 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 7,000-metre (23,000ft) mountain, the impact of which registered a magnitude of 5.2.
“Additional analysis of long-period seismic waves indicates that the seismic energy was instead generated by a glacial collapse and debris flow,” the US Geological Survey said.
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.
“These high temperatures would have weakened the snowpack, filled crevasses with water and thawed the bonds between ice and rock that hold these glaciers in place,” he told the Science Media Centre.
A series of intense heatwaves has hit the region since early this year and 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.
“Every increment of warming will multiply and intensify future hazards from cryosphere regions,” observed the Intergovernmental Panel on Climate Change in its sixth synthesis report. “Floods, landslides and freshwater shortages from glacier retreat and snow loss pose a serious threat to mountain regions across the world.”
