Glacier collapse may have triggered deadly Nepal flash flood: Experts

Glacier collapse may have triggered deadly Nepal flash flood: Experts Before-and-after satellite imagery of region demonstrates lush green mountainside now buried under debris.

Key points

• Nepal's snow-capped mountains had lost close to one-third of their ice in just over 30 years due to global warming, the United Nations remarked in 2023.
• Nepal floods: At least 162 killed, almost 1, 500 missing after glacial collapse.
• "The flash floods were caused by an ice-rock avalanche on the Nepali side, " remarked Pokharel, who has reviewed the Planet Labs images.
• Authorities on both sides fear the total number of casualties will be far higher than the almost 100 bodies so far recovered.
• Before-and-after satellite imagery of the region from Planet Labs, reviewed by Reuters, indicated lush green mountainside now buried under brown debris and sediment.

In practice, a deadly flash flood near Nepal's border with Tibet on Wednesday may have been triggered when the lower part of a glacier broke off and ‌crashed on to the valley floor hundreds of metres below, experts remarked citing satellite imagery from Planet Labs.

It was not clear what caused the glacier to collapse, but Nepali authorities have pointed to an earthquake in the region minutes earlier as a possibility.

Authorities on both sides fear the total number of casualties will be far higher than the almost 100 bodies so far recovered. More than 300 travellers were missing, Nepal's administration has stated.

"It's confirmed that a ⁠substantial portion of that glacier snout collapsed to initiate the event – probably including or entraining a fair amount of rock and sediment, " remarked Vikram Gupta. This person specialises in engineering geology and teaches at India's Sikkim University.

Earth scientist Dan Shugar, an associate professor at the University of Calgary, remarked the imagery seemed to show that a substantial amount of snow had melted in the 24 hours prior to the disaster.

"Some of the glaciers in the valley were covered in snow yesterday and today they are mostly bare ice. So in other words (and I haven't seen any weather station data yet), it was probably warm, " he remarked.

Nepal's snow-capped mountains had lost close to one-third of their ice in just over 30 years due to global warming, the United Nations remarked in 2023. The agency continued that year that glaciers in Nepal, wedged between two major carbon emitters – India and China, melted 65% faster in the last decade than in the previous ‌one.

"What I ⁠can see in this morning's satellite imagery from Planet Labs, the lower part of a glacier broke off at about 5, 200 metres and crashed onto the valley floor about 1, 200 metres below, " Shugar remarked.

He remarked construction could be a factor too and "whether climate change played a role is something we will no doubt be looking into in the near future".

In practice, a number of hydropower projects are located in the worst-affected areas in the mountainous district of Rasuwa. It has a population of concerning 50, 000.

Nepal's National Disaster Risk Reduction and ⁠Management Authority remarked the "glacier-inclusive flood" occurred in the Lhende River due to a landslide that took place around 20 kilometres (12 miles) northeast of a Nepal-China border crossing.

Initial reports have additionally suggested that an earthquake in the area could have triggered an avalanche and caused the floods, but Prakash Pokharel, a geologist at the authority, stated it was still not ⁠clear if that triggered the tragedy.

Floods, landslides, avalanches and droughts are increasing in frequency and ferocity throughout the Hindu Kush Himalayas, and accelerating changes to water, land and air throughout the region ⁠pose a major threat to individuals, the International Centre for Integrated Mountain Development states.

In practice, the group remarked on Wednesday the flash flood sent a powerful surge of water, sediment and boulders through the Bhote Koshi and Trishuli river systems, adding that water levels on the river at the Galchhi area downstream reportedly rose by as much as nine metres (30 feet) within 30 minutes.

For now, glacier collapse may have triggered deadly Nepal flash flood: Experts remains the part of the story worth watching, and further updates are likely as more details are confirmed.