Glacier Collapse Linked to Flash Flood
Preliminary scientific findings indicate that a glacier collapse may have triggered the devastating flash flood along the Nepal-Tibet border, drawing renewed attention to the rapid loss of Himalayan ice. At least 177 people have been killed in the disaster.
Early reports suggested that an earthquake had caused a landslide, which then triggered the flooding. However, the US Geological Survey later clarified that the event was associated with a “glacial collapse”, meaning a glacier or section of one broke apart.
The force created when the collapsed ice and debris struck the valley floor was strong enough to produce seismic activity measuring magnitude 5.2, according to USGS data and scientists studying the event.
Scientists Identify Glacier Near Langtang Lirung
Dr Simon Cook, a glacier specialist at the University of Dundee, told the BBC that his team had identified a collapse affecting the lower section of a glacier near Nepal’s Langtang Lirung peak, around 15km (9 miles) west of where the flooding occurred.
Cook said the glacier appeared to have collapsed towards the northwest before the resulting material moved westward downstream, potentially contributing to the devastating surge that swept through the valley.
An analysis by the International Centre for Integrated Mountain Development (ICIMOD) suggested that an ice-rock avalanche may have originated at high altitude. The debris, consisting of a large quantity of ice and rock, entered the Lende Khola, a tributary of the Bhote Koshi river.
The resulting surge carried water, sediment and large boulders downstream. ICIMOD reported that water levels in rivers farther downstream rose by between seven and nine metres within just 30 minutes, while several monitoring stations were either destroyed or damaged.
Landslide and River Surge May Have Combined
Professor Mike Searle of Oxford University said the sequence of events may have unfolded over several hours or even days rather than occurring as a single sudden event.
He suggested that a landslide could initially have blocked the river, allowing water to accumulate before the temporary barrier eventually failed and released a powerful flood carrying large quantities of debris.
The area’s steep terrain may also have increased the speed and destructive force of the water. Searle noted that Langtang Lirung is located along the high Himalayan crest, with extremely steep valleys on either side that could have channelled the flood downstream at considerable speed.
Cause of Glacier Collapse Remains Unclear Nepal-Tibet flash flood
Scientists have yet to establish exactly what caused the glacier to collapse on Wednesday. Searle said the Himalayan mountains continue to rise because of long-term tectonic activity, as one tectonic plate pushes against another.
As the mountains rise, glaciers can become increasingly steep, making sections more vulnerable to collapse. However, Searle said such failures generally involve smaller sections of ice that may temporarily obstruct rivers before being washed away.
The scale of Wednesday’s collapse appears to have been highly unusual, with Searle describing the apparent failure of the glacier as happening “in one go”. He said floods of this type occur frequently in the region, but events of such magnitude are rare.
Climate Change Raises Himalayan Risks Nepal-Tibet flash flood
Scientists have warned for years that rising temperatures are accelerating the loss of glaciers and the thawing of permafrost across the Himalayas. These changes can weaken mountain slopes and increase the risk of landslides, debris flows, glacier collapses and glacial lake outburst floods.
Searle said the disaster may have resulted from the interaction between Himalayan tectonic activity and a changing climate, with higher temperatures contributing to increasingly unstable glaciers and mountain environments.
An ICIMOD analysis released earlier this year found that glaciers across the Hindu Kush Himalaya region are losing ice at twice the rate recorded since 2000. Scientists say the accelerating loss of ice can increase the risk of flooding and other hazards downstream.
Previous Glacier Disasters Raise Concern Nepal-Tibet flash flood
Dr Cook noted that glacier collapses have contributed to destructive floods and landslides in countries including India, Switzerland and Italy in recent years.
In 2021, a major section of a Himalayan glacier collapsed in the Chamoli valley in northern India, sending water and debris downstream and killing about 200 people. Scientists later estimated that the energy released by the collapse was comparable to 15 atomic bombs.
Nepal has also experienced flooding linked to glacial hazards. The same wider region was affected last year when a glacial lake in Tibet burst, sending floodwaters downstream.
Mohd Farooq Azam, a cryosphere specialist with ICIMOD, said the growing frequency of hazards affecting the frozen parts of the Earth is becoming increasingly apparent, with the pace of environmental change accelerating.
Dr Cook cautioned that it is difficult to attribute any individual disaster directly to climate change. However, he said the growing pattern of such events suggests that warming could be contributing to the increased danger.
As global temperatures rise, glaciers shrink and snow melts more rapidly, while permafrost that helps stabilise mountain slopes can thaw and weaken. Scientists warn that these combined changes could increase the likelihood of landslides, debris flows, glacial meltwater surges, lake outbursts and glacier collapses across high-altitude regions.