Sudden Thaws in Mountain Glaciers: The Great Threat of Global Warming

The Nepal disaster clearly illustrates a problem that climate scientists have been warning about for years. The frozen structure of the Himalayas is destabilizing, exposing millions of people to increasingly unpredictable dangers. “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).

Read more A woman buried by mud and a man trapped in a tunnel rescued alive eleven days after the flood in Nepal

The event – with about 1,300 dead – is attributed to the collapse of part of a glacier (600 meters wide) with dragging of earth and rocks, which spread through various mountain rivers (the Lhende Khola), triggering the destructive chain of events. It generated a large wave of 100 kilometers that dragged everything in its path with a speed and force comparable to that of a tsunami (with heights up to 70 meters). However, usually, floods and inundations in the mountains originate from glacial lakes.

Glacial lakes are large accumulations of water of glacial origin, retained by sediments left by the glacier or by the ice itself. The material is very unstable and, therefore, there is a great risk of rupture capable of triggering large floods. But in Nepal, it was due to a direct collapse of the ice.

The collapse of a glacier can occur under any circumstance. Ice is unstable and we are talking about areas of steep orography. “But in a general context of glacier retreat due to warming, the chances are greater, because glaciers are more degraded, more water circulates inside them, and the ice is warmer and more plastic, so it can gain more acceleration,” says Ignacio López-Moreno. The village of Blatten, in the Swiss canton of Valais, was almost entirely 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, glaciologist at the University of Melbourne. “Permafrost, soil frozen all year round, acts as 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 worldwide. The floods they cause have become five times more frequent since 1950, according to an analysis of 493 studied cases carried out by a team of experts from the United Nations University; the average has gone from seven per decade to 34. This danger was already detected in Nepal. Last year, the sudden overflow of a glacial lake affected the same river system, causing nine deaths and leaving 24 missing.

Read more Alma de Petritxol in the Mercader passage

In 2021, a glacier in the Himalayas broke off, causing sudden floods in the Indian state of Uttarakhand and leaving 200 dead or missing. This region is a densely populated area, largely inhabited by vulnerable people, low-skilled migrants. There are increasingly more roads, hotels, and hydroelectric plants in the area, concentrated in valleys through which water, ice, and sediments can suddenly descend.

Warming is causing “irreversible” effects, including mountain glaciers, according to the latest report from the UN Intergovernmental Panel on Climate Change (2023). With warming of up to 3 degrees or less, “glaciers could lose more than a quarter of their mass by 2100” and raise sea levels between 9 and 13 centimeters, while “damaged or fragmented ecosystems can accelerate climate change.” Of the total global glacier mass loss recorded since the 1970s, more than 40% has occurred in just the last decade, according to the latest report from the United Nations Environment Programme.

The Himalayas (Nepal, India, China, Bhutan, and Pakistan) are warming at twice the global average rate, increasing the risk of avalanches, landslides, and floods in the region. In 2023, the UN stated that the mountains of Nepal have lost nearly a third of their ice in just over 30 years. An assessment published that same year revealed that the glaciers of the Hindu Kush-Himalaya had disappeared 65% faster between 2011 and 2020 than in the previous decade.

All this is happening in a context where the planet is about to exceed the 1.5 ºC warming threshold and extreme weather events have been repeated worldwide in recent months. To the overflow of glacial lakes and glacier collapse, heat waves, forest fires, and the emergence of El Niño loom on the horizon. We will have to act on several fronts, experts say: redouble efforts to reduce greenhouse gas emissions, adapt to this situation, and implement early warning systems to alert the population.

These risks persist wherever rapid glacial melting is observed. But this is a problem that the Andes do not escape. The overflow of the Palcacocha lagoon in Peru caused a violent mudslide in 1941 and caused the death of more than 1,800 people in Huaraz by destroying much of the city. Draining the lagoons, implementing alert systems, and planning the diversion of possible water and ice flow so they do not reach cities are some proposed solutions. Peru has lost 59% of its glaciers in the last six decades due to global warming and 528 glacial lakes at risk of overflow have been identified throughout the country.

Read more OKM, SME of the Year 2026 of Girona