More than 160 people have died and hundreds more are missing after a massive avalanche of water, ice, mud and rocks rushed more than 170 kilometers down the Bhote Koshi River Valley in Nepal. The valley is the main communication route between Kathmandu, in Nepal, and Lhasa, in Tibet. There was hardly any advance notice.
The images of the sudden flood loaded with debris are shocking. Unfortunately, it is not surprising. As an expert on glaciers, I have closely followed their accelerated retreat around the world as they melt, as well as the disasters they can cause. Initial analyzes suggest that the sudden collapse of a glacier triggered the catastrophe.
As climate change intensifies, glaciers around the world are melting, even in high-altitude regions like the Himalayas. The Himalayas are especially vulnerable, as the steep slopes of many of these tall mountains are made up of permafrost – rock and soil frozen for centuries. As temperatures rise, these slopes are beginning to melt or become destabilized. If an earthquake or landslide occurs, it can trigger a sudden and devastating debris flow.
It is too early to say that this was the exact cause. But we know that the vast ice reserves in the Himalayas – known as the world’s “third pole” because it contains the most snow and ice after the Arctic and Antarctic – are no longer safe.
What do we know about this catastrophe?
What happened in Nepal is probably due to a huge ice and rock slide that devastated a mountain pass and carried away ice, water, rocks, trees and soil.
The landslide was so large that it was initially thought to be an earthquake, as the seismic energy was recorded as a magnitude 4.4 quake on seismographs.
When it arrived at the port of Gyirong – a border crossing between China and Nepal – the wall of debris resembled a tsunami of land. Early estimates suggest the wave could have been 30 meters high.
What are the possible causes?
Sometimes disasters like these can occur when meltwater from a glacier, trapped in a lake by a landslide, overflows. One of these phenomena, known as a “glacial lake outburst flood,” affected Nepal in 2024.
However, early analysis suggests that is not the case here. Satellite images indicate that the landslide could have eroded large parts of a glacier, causing it to collapse.
We still don’t know what caused the glacier to collapse. However, glaciers around the world are generally receding, which can lead to disasters such as floods and debris flows.
Last year, a smaller flood hit the same district in Nepal, killing nine people. Also last year, a melting glacier in Switzerland caused a huge debris flow that destroyed the village of Blatten. In 2023, a landslide and subsequent flood in my home country, Georgia, killed 33 people at a mountain station.
But this disaster is one of the most serious to date.
Permafrost is vulnerable
High-altitude glaciers in the Himalayas may respond to climate change differently than glaciers located at lower altitudes or in relatively warmer regions. Thawing and degradation of permafrost may also contribute to making the steep slopes of the Himalayas less stable.
Permafrost is soil composed of rock, soil and ice that has remained at or below 0°C for many years. As the climate warms, the ground can thaw, weakening the ice that helps bind rock and soil.
On steep mountain slopes, this loss of frozen soil can make the slopes less stable and increase the likelihood of rock falls, landslides, and other forms of ground movement. An earthquake, rockfall, or other disturbance can then trigger rapid downhill movement of rocks, soil, and debris.
Can these disasters be prevented?
There were no fatalities when the Swiss glacier collapsed. Thanks to early warning systems, authorities evacuated residents before the collapse occurred.
As temperatures rise and climate-related disasters become more frequent or severe in some regions, early warning systems will become increasingly important for towns and villages near thawing glaciers or permafrost. These systems can monitor rapidly rising river levels, heavy rain and seismic waves to alert authorities before a disaster strikes.
However, installing and maintaining effective early warning systems can require significant investment, which is challenging for low-income and developing countries. The good news is that the Green Climate Fund announced last year that it would allocate funding to improve monitoring systems in Nepal.
But there is another problem. Water from melting Himalayan glaciers feeds rivers that are vital to billions of people in Nepal, Pakistan, India and China. As the climate warms, increased glacial melt can temporarily increase river flows and, in some places, contribute to the risk of flooding.
However, if the glaciers continue to shrink in parallel, their contribution could decrease over time and cause less water availability, especially during the dry season.
Rapidly reducing greenhouse gas emissions, investing in early warning systems and better monitoring vulnerable mountain regions can help communities prepare. These measures will not prevent all disasters, but they can save lives and give people more opportunities to adapt to climate change.
Levan Tielidze, Research Fellow in Glacial Geomorphology, Monash University
This article was originally published on The Conversation. Read the original.
