Glacier Collapse Likely Triggered Nepal Flash Flood, Experts Say

A catastrophic flash flood that swept through a mountainous region of Nepal near the Tibet border on Wednesday was likely triggered by the collapse of a glacier, according to experts reviewing satellite imagery. The images, captured by Planet Labs, show that the lower portion of a glacier broke off at an altitude of about 5,200 metres and crashed onto the valley floor roughly 1,200 metres below.

The event, described by one geologist as an "ice-rock avalanche," sent a powerful surge of water, sediment, and boulders through the Bhote Koshi and Trishuli river systems. Water levels downstream at Galchhi reportedly rose by as much as nine metres within 30 minutes.

Nepal's National Disaster Risk Reduction and Management Authority said the flood occurred in the Lhende River due to a landslide about 20 kilometres northeast of a Nepal-China border crossing. The exact cause of the glacier's collapse remains unclear, though a regional earthquake minutes earlier is being considered as a possible trigger. Prakash Pokharel, a geologist with the authority, said it was still uncertain whether the quake played a role.

Satellite imagery reviewed by experts shows a lush green mountainside now buried under brown debris and sediment. Vikram Gupta, who specialises in engineering geology at Sikkim University in India, said it was confirmed that a substantial portion of the glacier snout collapsed, likely incorporating rock and sediment.

Dan Shugar, an associate professor at the University of Calgary, noted that the imagery indicated a large amount of snow had melted in the 24 hours before the disaster, suggesting unusually warm conditions. He added that construction activity in the area and the potential influence of climate change would be investigated.

The disaster has raised fears of a high death toll. Nearly 100 bodies have been recovered so far, but more than 300 travellers remain missing, according to Nepal's government. The worst-affected areas are in Rasuwa district, home to several hydropower projects and a population of about 50,000.

Nepal's glaciers have been melting at an alarming rate. The United Nations reported in 2023 that the country's snow-capped mountains lost nearly one-third of their ice in just over three decades, with melting accelerating by 65% in the last decade compared to the previous one. The International Centre for Integrated Mountain Development warns that floods, landslides, avalanches, and droughts are becoming more frequent and severe across the Hindu Kush Himalayas, posing a major threat to the region's people.