Nepal glacier collapse followed record heat, expert says

The August 26 glacier and mountain collapse on the Nepal-China border followed unprecedented heat for the time of year at the collapse site, according to meteorological data analysed by Berkeley Earth chief scientist Robert Rohde, though no direct link to the disaster has been established.

The disaster has killed at least 1,399 people and left more than 5,500 missing, according to the latest figures in the supplied published reporting. It sent water, mud and debris through communities, roads and hydropower sites after part of the mountain failed at an altitude of about 5,200 metres.

Rohde reconstructed local temperatures using the Copernicus programme's ERA5 climate model and data from 14 high-altitude weather stations located between nine and 140 kilometres from the collapsed glacier. He estimated that average temperatures on the glacier were around 5C between August 21 and 26.

The same six-day period had not exceeded 4.0C in more than 55 years of data recording. Rohde calculated that, without the additional heat brought by climate change, a comparable temperature pattern would probably occur only once in a few thousand years.

AFP's analysis of Copernicus data dating back to 1970 also found that the collapse came during the Langtang region's fourth-hottest summer on record.

French climatologist Valerie Masson-Delmotte said the hot conditions could help explain permafrost thaw and combined slope and glacier collapse. Permafrost can act as ice cement holding rock faces together, and its degradation can make them less stable.

Etienne Berthier, a glaciologist at France's CNRS research agency, said satellite images showed significant snowmelt in the days before the disaster, providing liquid water that could enter mountain fractures and facilitate landslides.

Researchers remain cautious about the exact role of the heat. Kristen Cook, a geomorphologist at Grenoble Alpes University, said it was not as simple as high temperature automatically causing collapse. She said that if temperature acted as a trigger, the rock may already have been close to failure.

Scientists are examining small movements seen in the mountain in the years before the collapse and how they interacted with temperature changes. Rohde said proving that rock near the fracture plane was significantly weakened by meltwater or permafrost thaw would be a stronger indication of climate change's role.