Scientists have warned that landslides and glacial collapses like those behind this week’s devastating flooding in Nepal and Tibet are likely to become more common as a result of climate change.
Huge waves of water and debris swept away people, roads and buildings, leaving more than 600 dead, most of them in Nepal but a small number in Tibet, and many more missing.
Rescue efforts continue, though they are sometimes interrupted by fears of further floods amid concerns that lakes in the area could overflow.
The landslide and glacier collapse is thought to have originated on the Langtang Lirung peak in Nepal, which is part of the Himalayas and around 15km away from the area around the Nepal-China border hit by floods.
Himalayan glaciers have been “retreating like crazy” as the climate warms, according to Mike Searle, a professor of earth sciences at the University of Oxford.
Along with the retreat of glaciers, a related problem is the thawing of mountain permafrost, with the ice that holds together the shattered rock surface material of mountains melting.
This can cause a landslide from the mountain that shears off a glacier, as is thought to have happened this week.
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An elderly survivor is transported to a safer place in heavy machinery following flash flood and mudslide at Trishuli in Nuwakot district, Nepal. Reuters -
A flood survivor returns to home following a flash flood in Devighat Village, Nuwakot district, Nepal. EPA -
Houses lying deluged in sludge after flash floods at Devighat, Bidur Municipality, along the confluence of the Trishuli and Tadi rivers in Nepal's Nuwakot district. AFP -
A flood survivor returns to home following a flash flood in Devighat Village, Nuwakot district, Nepal. EPA -
A child, who was airlifted from Rasuwa district, receives first-aid at a mobile hospital inside the Maithali Barrack, an army training centre, which also serves as a primary base to airlift survivors following flash floods and mudslide at Trishuli in Nuwakot district, Nepal. Reuters -
A CCTV footage shows people running away as wall of mud and water destroys buildings in a valley at Nepal-China border, in Gyirong, Tibet region, China. Reuters -
Relatives of flood victims stand outside the army base where survivors are brought by helicopters following a flash flood in Devighat Village, Nuwakot district, Nepal. EPA -
A drone view shows mud covering buildings following a flash flood in Trishuli, Nuwakot district, Nepal. Reuters -
A woman searches for her belongings at a damaged shop following flash floods and a mudslide in Trishuli, Nuwakot district, Nepal. Reuters -
Army personnel walk past a helicopter landing with rescued flood-affected residents from flash floods, at an army camp in Battar Bazar town in Nepal's Nuwakot district . AFP -
Women carry belongings from their damaged homes after a flash flood and a mudslide, in Galchhi, Nepal. Reuters
'Apocalyptic event'
“You have got this precarious glacier perched on the side of a really steep mountain characterised by permafrost that’s melting. You have this cocktail of factors that leads to this totally apocalyptic event,” said Dr Richard Waller, a senior lecturer in physical geography at Keele University in the UK.
Images suggest that there was snow a day or two before on the surface of glaciers in the area, said Dr Ethan Lee, a postdoctoral researcher in glacial modelling at the University of Sheffield in the UK, but none on the day of the event.
“So a major warming event occurred, potentially allowing water to enter the glacier through crevasses (openings in the ice itself), and if more water enters the base of the ice, it can lubricate it and allow it to slide along the rock more easily,” he said.
Another factor, said Prof Searle, who several decades ago climbed high up the Langtang Lirung peak, is the continued growth of mountains in the area because of tectonic activity.
“We know from GPS that these mountains are still rising,” he said. This makes the glaciers steeper and more at risk of falling.
The huge waves of water that caused such destruction were probably not an immediate result of the collapse of the glacier, he said, as debris probably created a dam in the river and, behind it, a lake, which may have taken two days to fill up.
“Lakes build up behind rock debris flows, and when the lake breaches its dam, it causes catastrophic floods, as we have seen,” Prof Searle said. “The valleys are steep – the water has nowhere to go, so it builds up to a tidal wave.”
Raising the alarm
Dr Waller said he hoped that this week’s devastation would lead to “detailed hazard mapping” to identify other locations at risk of similar events, as this could allow for an early warning of potential disasters.
He drew a contrast between this week’s events on the Nepal-Tibet border with what happened in May last year at the Swiss mountain village of Blatten, which was evacuated more than a week before it was destroyed by a glacial collapse and landslide.
“They were actively monitoring and they evacuated the village in advance,” he said. “I’m hoping that’s something that will come out of this as a way of safeguarding lives long term.”
The Khumbu glacier, located on the slopes of Mount Everest, the world’s highest glacier, is the only glacier in the area currently monitored in detail, Prof Searle said.
The locations that have suffered damage are particularly at risk because they are in river valleys, Prof Searle added, so building roads and houses higher up would be safer, although steep valley sides make this difficult.
“More aid is desperately needed, especially to UN organisations,” he added. “The cutting off of USAID [the United States Agency for International Development] has had a disastrous effect on poor countries like Nepal.”
Impact of global warming
Dr Lee said that while this week’s events could not be directly linked to climate change, warming did have “a destabilising effect that can be chained together”.
“Snow melt leads to more water entering the system, continual shrinking of the glaciers and retreating to steeper terrain, permafrost melting and thawing, weakening the ground, that can increase the occurrence of landslides and debris flows,” he said.
There have been previous examples of this, he said, including the 2021 Uttarakhand flood in north-eastern India, which caused scores of deaths, and the 2022 collapse of a block of glacial ice on Marmolada, the highest mountain in the Dolomites mountain range in north-eastern Italy, which also resulted in fatalities.
“So we have seen lots of similar events have occurred and it is likely these will continue going into the future,” he said.
Dr Diana Francis, an associate professor and head of the Environmental and Geophysical Sciences laboratory at Khalifa University in Abu Dhabi, said glaciers in mountainous regions were “even more sensitive than those in polar regions” to climate change.
“They are surrounded by land and don’t have the protective buffer that glaciers in the poles have, which is the sea ice margin,” she said
“Glaciers around the world have been retreating at an accelerated rate, add to this the fact that global warming is happening at a faster rate in mountainous regions, it is expected that glacier disintegration and collapse will become more frequent.”
She recommended a global mapping of populated areas in regions prone to glacial collapses so that measures could be put in place to reduce risks.
