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A massive collapse of rock and ice high in the Himalayas is emerging as the likely trigger of the devastating flash floods that struck the Nepal-Tibet border this week, with scientists warning that climate change may be increasing the instability of the region’s already fragile mountain environment.
The disaster unfolded on Wednesday after what experts believe was a large ice-rock avalanche on the northern slopes of Nepal’s Langtang Lirung peak. The collapsing mass appears to have plunged hundreds of metres into the valley below, sending water, sediment and boulders surging through river systems and settlements downstream.
At least 165 people have been confirmed dead, while nearly 1,500 remain missing, including hundreds of foreign nationals. Authorities fear the final toll could rise significantly as rescue teams continue searching affected areas.
Satellite imagery reviewed by experts shows a dramatic transformation of the landscape, with previously green mountainsides buried beneath vast amounts of debris and sediment.
Scientists examining the images say a substantial section of the lower part of a glacier appears to have broken away at an altitude of around 5,200 metres before crashing roughly 1,200 metres onto the valley floor.
Nepalese disaster authorities have described the event as an “ice-rock avalanche”, saying the resulting flood travelled through the Lhende River before feeding into the Bhote Koshi and Trishuli river systems.
The force of the surge was immense. In the Galchhi area downstream, water levels reportedly rose by as much as nine metres in just 30 minutes.
Several major hydropower projects and other infrastructure were damaged, while river channels were altered more than 100 kilometres downstream. Infrastructure around the Gyirong Port trade hub on the Nepal-China border was also affected.
Exact trigger remains uncertain
Researchers are still working to determine what caused the initial collapse.
Nepalese officials initially considered an earthquake as a possible explanation. However, the US Geological Survey later concluded that the seismic signal detected in the area was likely generated by the collapse itself, rather than by an earthquake that preceded it.
Satellite images also suggest unusually rapid snow melt in the hours before the disaster.
Earth scientist Dan Shugar of the University of Calgary said glaciers that had appeared snow-covered shortly beforehand were largely exposed as bare ice by the following day, indicating that temperatures may have been particularly warm.
Scientists have stressed, however, that it is too early to attribute the disaster directly to climate change.
Other factors, including local geological conditions, seismic activity and human construction, may also have contributed.
Climate change could be increasing instability
Although the immediate cause remains under investigation, researchers say rising temperatures are creating conditions that can make high-altitude slopes more vulnerable to sudden collapse.
Warming can melt the ice that helps support steep rock faces, increase the amount of meltwater flowing through cracks and change cycles of freezing, thawing and rainfall. Over time, those changes can weaken mountainsides and make avalanches or rockfalls more likely.
Simon Cox, chief scientist with Earth Sciences New Zealand’s Mountains to Sea programme, said climate change was increasingly creating conditions capable of destabilising high-mountain rock and ice.
Scientists have also pointed to the possibility that this week’s disaster was a “compound event”, in which several factors combined to produce a far more destructive outcome.
Benjamin Horton, dean of the School of Energy and Environment at the City University of Hong Kong, said hazards such as seismic activity can interact with long-term changes including glacier retreat, thawing permafrost and slope instability.
Such overlapping risks, researchers say, are becoming increasingly important in the Himalayas.
Himalayan ice retreat accelerating
The disaster comes amid mounting concern over the rapid loss of ice across Nepal and the wider Hindu Kush Himalayan region.
The United Nations reported in 2023 that Nepal’s snow-covered mountains had lost close to one-third of their ice over slightly more than three decades.
It also found that the country’s glaciers had melted around 65% faster during the preceding decade than during the decade before that.
Floods, landslides, avalanches and droughts are also becoming more frequent and severe across the Hindu Kush Himalayas, according to the International Centre for Integrated Mountain Development.
Similar disasters have already struck the region in recent years, including a glacial lake outburst near the Sherpa village of Thame in Nepal in 2024, a major flood in Sikkim, India, in 2023, and another flood near Gyirong on the Tibet-Nepal border in 2025.
Experts warn that as mountain temperatures continue to rise, the region’s cryosphere – the frozen part of the Earth’s surface – is becoming increasingly unstable.
For communities living downstream, this means disasters may no longer come from a single identifiable source. Instead, melting glaciers, unstable slopes, extreme weather and geological activity can combine to create cascading hazards capable of travelling far beyond the mountains where they begin.
Scientists say understanding those connections will be crucial if Himalayan communities are to improve early-warning systems, protect infrastructure and prepare for increasingly complex disasters.
Also read: Nepal-Tibet floods leave at least 162 dead
Source: Reuters
