A catastrophic rock-and-ice avalanche that triggered devastating floods along Nepal's border with China last month was made more likely by global warming, which weakened glaciers and mountain permafrost, an international team of scientists said Thursday.

The assessment, one of the first comprehensive scientific studies of the August 26 catastrophe, found that climate change was a destabilising factor acting on a mountain slope already vulnerable because of its underlying geology.

The disaster began when about two square kilometres of rock wall and glacier ice collapsed from Langtang Lirung at an altitude of about 5,150 metres.

The collapsing mass plunged roughly 1,400 metres to the valley floor, releasing energy equivalent to a magnitude 5.5 earthquake and producing seismic waves initially detected as an earthquake-like signal.

The avalanche rapidly transformed into a debris flood, carrying rock, ice, sediment and water down the Bhotekoshi and Trishuli river systems.

The torrent reached the Rasuwagadhi border, about 22 kilometres downstream, in seven minutes, travelling at an average speed of 188 kilometres per hour, the researchers said.

It then swept through Timure and Syabrubesi before reaching the Trishuli valley and devastating communities including Betrawati and Trishuli Bazaar.

The flood travelled about 200 kilometres to Devghat in less than seven hours, where river discharge more than doubled to about 5,850 cubic metres per second. Around 30.5 million cubic metres of sediment and debris were deposited along the disaster corridor.

Nepal's disaster authorities had recorded more than 1,300 deaths and more than 5,000 people missing by September 14, while thousands more had been rescued or treated.

The international team included researchers from Nepal, Pakistan, Britain, Ireland, Sweden, Denmark, Norway, the United States, New Zealand and the Netherlands, with expertise ranging from glaciology and mountain hydrology to climate science and seismology.

The scientists said the geological structure ultimately controlled where and how the slope failed, while several factors may have contributed to its instability.

A magnitude 7.8 earthquake in 2015 triggered another major rock-and-ice avalanche in the Langtang region and may have weakened the mountain's underlying rock mass over the longer term, although its specific contribution to the 2026 collapse could not yet be established.

The researchers also identified warming temperatures, permafrost degradation, glacier thinning and changing precipitation patterns as potential contributing factors.

Glaciers in the region have been losing more than half a metre in thickness each year, while the retreat of the Langtang-Lirung glacier has accelerated since 2010.

The freezing level has also risen by about 100 metres per decade in recent decades during the monsoon and post-monsoon seasons, increasing the potential for permafrost thaw and glacier loss.

July and August 2026 were unusually warm around the disaster site. The researchers found that human-caused climate change had increased temperatures during those months by about 1.5 degrees Celsius compared with a climate 1.4C cooler than today.

But the scientists stressed that they had not determined whether the avalanche would have occurred without human-caused climate change.

Instead, they said climate change should be understood as a factor that can increase instability in already vulnerable mountain terrain.

The assessment also concluded that the disaster was beyond the design and predictive limits of existing warning systems, highlighting the difficulty of protecting communities from extremely rapid and cascading mountain hazards.

It called for stronger high-altitude monitoring, earth observation, risk communication and data sharing between countries, alongside greater support for communities facing climate-related loss and damage.