A deadly flash flood that occurred on Wednesday near Nepal’s border with Tibet could have been triggered when the lower part of a glacier broke off and crashed into the valley floor, hundreds of meters below, experts said, citing satellite images from Planet Labs.
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It is unclear what caused the glacier to break off, but Nepalese authorities have pointed to an earthquake that occurred in the region a few minutes earlier as a possible cause. Authorities on both sides fear that the total number of victims will be much higher than the nearly 100 bodies recovered so far. According to the Government of Nepal, more than 300 travelers are still missing.
Satellite images of the region before and after the event, provided by Planet Labs and analyzed by Reuters, showed a lush green mountainside now buried under brown debris and sediment. “A significant portion of the glacier tongue has been confirmed to have collapsed, triggering the event – likely including or carrying with it a considerable amount of rock and sediment,” said Vikram Gupta, a geological engineering specialist and professor at Sikkim University, India.
Geoscientist Dan Shugar, an associate professor at the University of Calgary, noted that the images seemed to indicate that a large amount of snow had melted in the 24 hours prior to the disaster. “Some of the glaciers in the valley were snow-covered yesterday and today they look mostly like bare ice. So, in other words (and I haven’t seen any weather station data yet), it was probably hot,” he said.
Nepal’s snowy mountains had lost nearly a third of their ice in just over 30 years due to global warming, according to the United Nations in 2023. The organization added that same year that Nepal’s glaciers, located between two major carbon emitters, India and China, melted 65% faster in the last decade than in the previous one. “From what I can see in this morning’s satellite images from Planet Labs, the lower part of a glacier broke off at about 5,200 meters and crashed into the valley floor, about 1,200 meters below,” Shugar explained. He noted that construction could also be a factor and that “we will certainly investigate in the near future whether climate change has played a role in this.”
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Several hydroelectric projects are located in the most affected areas of the mountainous Rasuwa district, which has a population of about 50,000. Nepal’s National Disaster Risk Reduction and Management Authority said the “glacial material flood” occurred in the Lhende River due to a landslide that took place about 20 kilometers northeast of a border crossing between Nepal and China.
Initial reports have also suggested that an earthquake in the area could have triggered an avalanche and caused the floods, but Prakash Pokharel, a geologist with the authority, said it was still unclear if that was what triggered the tragedy. “The flash floods were caused by an ice and rock avalanche on the Nepalese side,” said Pokharel, who has analyzed the Planet Labs images.
Floods, landslides, avalanches, and droughts are increasing in frequency and ferocity across the Hindu Kush-Himalaya, and accelerated changes in water, land, and air throughout the region pose a serious threat to the population, says the International Centre for Integrated Mountain Development.
The organization noted this Wednesday that the avalanche caused a powerful surge of water, sediment, and rocks through the Bhote Koshi and Trishuli river systems, adding that, according to reports, the water level in the river, in the downstream Galchhi area, rose up to nine meters in just 30 minutes.
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