The Nepal disaster clearly illustrates a problem that climate scientists have been warning about for years. The icy structure of the Himalayas is destabilizing, exposing millions of people to dangers that are increasingly difficult to predict. “Warming can lead to more glacier collapses and more formation of glacial lakes that can collapse,” summarizes Ignacio López-Moreno, researcher at the Pyrenean Institute of Ecology. (CSIC).
The event - with some 1,300 deaths - is attributed to the collapse of part of a glacier (600 meters wide) with earth and rocks dragged, which spread through various mountain rivers (the Lhende Khola), until triggering the destructive succession of events. It generated a large wave of 100 kilometers that swept away everything in its path with a speed and force comparable to that of a tsunami (with heights of up to 70 meters). On the other hand, usually, floods and floods in the mountains have their origin in glacial lakes.
Glacial lakes are large accumulations of water of glacial origin, retained by the sediments left by the glacier or by the ice itself. The material is very unstable and, therefore, there is a great risk of rupture and capable of triggering large floods. But in Nepal it has been due to a direct collapse of the ice.
The collapse of a glacier can occur in any circumstance. The ice is unstable and we are talking about areas of steep orography. “But in a general framework of glacier retreat due to warming, the possibilities are greater, because the glaciers are more degraded, more water circulates inside them and the ice is warmer and more plastic, so it can accelerate more,” says Ignacio López-Moreno. The town of Blatten, in the Swiss canton of Valais, was almost completely buried after an avalanche of ice, rocks and mud due to the collapse of the Birch glacier that occurred in May 2025.
“Mountain permafrost is degrading due to global warming,” says Carl-Friedrich Schleussner, a glaciologist at the University of Melbourne. “Permafrost, frozen ground all year round, acts like a glue that holds rocks and, sometimes, adjacent glaciers together,” adds this expert. Therefore, a more destructive effect can be caused, because the soils are not as cohesive.
Glacial lakes are expanding around the world. The flooding they cause has become five times more frequent since 1950, according to an analysis of 493 cases studied by a team of experts from the United Nations University; It has gone from an average of seven per decade to 34. This danger has already been detected in Nepal. Last year, the sudden overflow of a glacial lake affected the same river system, causing nine deaths and leaving 24 missing.
In 2021, a Himalayan glacier calved, causing flash floods in the Indian state of Uttarakhand and leaving 200 dead or missing. This region is a highly populated area, largely inhabited by vulnerable people, low-skilled migrants. There are more and more roads, hotels and hydroelectric plants in the area, concentrated in valleys where water, ice and sediment can suddenly descend.
Warming is causing “irreversible” effects, including mountain glaciers, according to the latest report from the UN Intergovernmental Panel on Change (2023). With warming of up to 3 degrees or less, “glaciers could lose more than a quarter of their mass by the year 2100” and raise sea levels between 9 and 13 centimeters, while “damaged or fragmented ecosystems can accelerate climate change.” Of the total global loss of glacier mass recorded since the 1970s, more than 40% has occurred in the last decade alone, according to the latest report from the United Nations Environment Programme.
The Himalayas (Nepal, India, China, Bhutan and Pakistan) are warming twice as fast as the global average, increasing the risk of avalanches, landslides and flooding in the region. In 2023, the UN stated that Nepal's mountains have lost about a third of their ice in just over 30 years. An assessment published that same year found that glaciers in the Hindu Kush-Himalaya had disappeared 65% faster between 2011 and 2020 than in the previous decade.
All this occurs in a context in which the planet is about to exceed the warming threshold of 1.5 ºC and the extreme weather events witnessed around the world in recent months are repeated. The overflow of glacial lakes and the collapse of glaciers are joined by heat waves, forest fires, and the emergence of El Niño is looming on the horizon. We will have to act on several fronts, experts say: redouble efforts to reduce emissions of gases that heat the atmosphere, adapt to this situation and implement early warnings to warn the population.
These risks persist wherever rapid glacial melt is observed. But this is a problem from which the Andes do not escape. The overflow of the Palcacocha lagoon in Peru caused a violent flood in 1941 and caused the death of more than 1,800 people in Huaraz by destroying a large part of the city. Draining the lagoons, implementing warning systems and planning the diversion of the possible flow of water and ice so that it does not reach the cities are some proposed solutions. Peru has lost 59% of its glaciers in the last six decades due to global warming and 528 glacial lagoons have been identified at risk of overflowing throughout the country.
