Glacier collapse likely caused deadly Nepal-Tibet floods, scientists say

The catastrophic flash floods that struck the Nepal-Tibet border on Wednesday, killing at least 177 people, were most likely caused by a collapsed glacier, scientists have told the BBC. Initial reports of an earthquake gave way to a different explanation when the US Geological Survey clarified that the disaster was the result of a “glacial collapse”—a phenomenon in which a glacier or part of it disintegrates. The impact of the falling ice striking the valley floor was so powerful that it registered as a magnitude 5.2 tremor on seismic instruments.

Dr Simon Cook, a glacier expert at the University of Dundee, told the BBC that his team had identified the collapse of the lower section of a glacier near the Langtang Lirung peak, approximately 15km west of the flood site. He estimated that the ice disintegrated in a northwesterly direction before travelling westwards downstream. An analysis by the International Centre for Integrated Mountain Development (ICIMOD), an intergovernmental scientific institution, found evidence of “an ice-rock avalanche originating from a high-altitude area”, which sent a large volume of ice and rock debris into the Lende Khola, a tributary of the Bhote Koshi river.

The sudden influx generated a surge in the river carrying water, sediment and enormous boulders downstream. ICIMOD determined that water levels rose between seven and nine metres within just 30 minutes, with several monitoring stations washed away or destroyed. The area, flanked by steep mountains, funnelled the debris and water at a terrifying speed, as aerial footage of the aftermath confirmed. The precise cause of the glacier’s collapse remains unclear, but scientists have long warned that warming temperatures and climate change are rapidly melting ice and permafrost in the Himalayas.

A separate ICIMOD analysis released earlier this year found that Hindu Kush Himalaya glaciers are now losing ice at double the rate observed since 2000, exacerbating flood risks. Dr Cook noted that similar incidents of floods and landslides caused by glacier collapses have occurred in India, Switzerland and Italy in recent years. In 2021, a large chunk of a Himalayan glacier collapsed in the Chamoli valley of northern India, sending a cascade of debris and water downstream that killed 200 people; scientists later estimated the impact as equivalent to 15 atomic bombs. Even in Nepal, the same region experienced flooding last year after a glacial lake in Tibet burst its banks.

Mohd Farooq Azam, a specialist with ICIMOD, said the increasing frequency of hazards in the cryosphere—the frozen parts of the Earth—“is becoming more visible than ever before. The pace of change is so rapid that current efforts are struggling to keep up.” While it is difficult to attribute any single event directly to climate change, Dr Cook observed that the pattern of such incidents is deeply concerning. “The logic is that with a warming planet, you will see shrinking glaciers, lots of snow melt. The permafrost that is partially holding some mountainsides together is warming and thawing and degrading. So you are going to get more landslides, debris flows, glacial meltwater, lake outbursts, glacier collapses, because climate warming ultimately destabilises these high mountain environments.”