Nepal flood toll rises to 177 as glacier collapse unleashes ‘tsunami of dirt’

The death toll from catastrophic flash floods in Nepal rose to at least 177 on Thursday as rescuers searched through vast fields of mud and debris for hundreds of people still missing.

The scientists meanwhile are piecing together how the collapse of a Himalayan glacier unleashed a torrent powerful enough to bury settlements and tear apart bridges.

Nepal Police said 12 more bodies had been recovered, taking the confirmed toll to 177, according to local media reports. The National Disaster Risk Reduction and Management Authority said around 826 people remained unaccounted for.

The missing include 579 tourists, as well as workers at hydropower plants and customs facilities and members of Nepal's security forces. Nearly 300 Indian tourists are believed to be missing, Foreign Minister Shisir Khanal said, many of them travelling towards the sacred Kailash Mansarovar area in Tibet or Gosainkunda in Nepal.

Reuters reported that the wider disaster, extending across Nepal and China's Tibet region, had left nearly 1,500 people missing, including more than 700 foreigners.

The scale of the missing means the death toll could rise considerably as rescuers reach areas cut off by destroyed roads and bridges.

The disaster began on Wednesday morning high in the Himalayas near the Nepal-Tibet border.

An enormous section of glacier, mixed with rock, broke away and plunged roughly 1.2 kilometres down into the valley below, according to preliminary satellite analysis cited by experts.

The impact sent ice, rock, water and pulverised earth rushing into the Lhende Khola river system. The surge travelled into the Bhote Koshi and then the Trishuli, transforming mountain rivers into fast-moving channels of mud and debris.

A sudden disaster

What followed was less a conventional flood than a moving wall of earth.

The Conversation described the phenomenon as a “tsunami of dirt”: a debris flow carrying an enormous concentration of sediment, rocks, trees and ice.

Such flows can behave very differently from ordinary floodwater, acquiring enough density and force to move boulders, demolish concrete structures and bury buildings rather than merely inundate them.

The first surge hit Timure, near the Rasuwagadhi crossing with China. It then barrelled downstream through the narrow Himalayan valleys, where settlements, roads, bridges, hydropower installations and hotels sit close to rivers because steep mountains leave little usable land.

The geography effectively funnelled the torrent.

Al Jazeera reported that the Trishuli River rose by as much as nine metres in just 30 minutes as the surge travelled downstream. Flooding subsequently spread through Rasuwa, Nuwakot, Dhading and other districts.

The scale of the initial collapse was so great that seismic monitoring systems detected it.

Early reports suggested a magnitude-4.4 earthquake might have triggered the catastrophe. Nepalese officials initially raised that possibility as they tried to understand what had happened.

The US Geological Survey later reached a different conclusion.

It said there had been no earthquake. The seismic signal detected at 8:37 a.m. local time was generated by the enormous collapse of glacial ice and rock itself and the subsequent debris flow. Further analysis put the seismic event associated with the collapse at magnitude 5.2.

Reuters similarly reported that the lower portion of a glacier collapsed onto the valley floor, producing an avalanche of ice and rock that swept into the Lhende Khola before generating high-speed flooding downstream.

Nepalese disaster officials are also examining whether the avalanche temporarily blocked the Lhende River.

A preliminary assessment by the country's disaster authority suggested the ice-rock avalanche may have created a natural dam before accumulated water and debris broke through or overtopped the obstruction, dramatically magnifying the flood downstream.

The precise mechanics remain under investigation.

A result of changing climate

What is increasingly clear, however, is that this was not primarily a disaster caused by unusually heavy rain. It originated high in the mountains with a catastrophic failure of ice and rock.

Climate change cannot yet be identified as the direct cause of this particular collapse, scientists have cautioned. But the disaster occurred in one of the fastest-warming mountain regions on Earth.

The Himalayas are warming substantially faster than the global average, while glaciers across the Hindu Kush Himalaya have been shrinking rapidly. Research cited by the BBC and other media has documented accelerating ice loss across the region.

The United Nations has previously estimated that Nepal's mountains lost nearly one-third of their ice over roughly three decades.

A major assessment of the Hindu Kush Himalaya found glaciers disappeared 65% faster between 2011 and 2020 than during the preceding decade.

That matters because warming can destabilise mountain landscapes in several ways.

As glaciers retreat, they remove ice that has helped support steep slopes. Meltwater can penetrate cracks in ice and rock. Permafrost that effectively glues mountain material together can thaw. Water can also accumulate around retreating glaciers, creating additional flood hazards.

Satellite observations before Wednesday's collapse showed unusually warm conditions around the affected glacier, with diminishing snow cover exposing more bare ice, according to media reports citing researchers.

Scientists are investigating whether melting contributed to the instability, although they have stressed that a direct climatic attribution would require further study.

For rescuers, the immediate problem is more physical.

Mud several metres deep covers parts of affected settlements. Roads have disappeared. At least 35 motorable bridges and 45 suspension bridges were reported damaged, along with around 40 kilometres of roads.

Major transport routes linking Kathmandu with northern and central districts have been disrupted.

More than 5,000 army and police personnel have been mobilised, Reuters reported. Helicopters have been dropping food, tents and emergency supplies, while at least 125 people had been rescued by Thursday, including foreign nationals.

India has sent emergency supplies, while the United Nations has begun mobilising personnel and relief materials. South Korea is sending a rapid-response team after Korean workers at a hydropower project were reported missing.

Across the border, China's Tibet region has also suffered extensive destruction around Gyirong, where roads, communications and electricity infrastructure were damaged.

The catastrophe has also sent warnings hundreds of kilometres downstream.

Authorities in India's Bihar state evacuated thousands of people as the surge moved through the interconnected Himalayan river system towards the plains.

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