High mountain glaciers formed in the ice age are retreating and becoming unstable as the burning of fossil fuels heats the climate and leads to a decline in snowfall.

The instability creates the conditions for large glacial sections to collapse, triggering ice and rock avalanches that can dam river valleys before tidal waves of water are released.

Following the glacier collapse that triggered what is known as a mountain tsunami in Nepal and Tibet on August 26, thousands are still missing and feared dead. Unlike the 2025 glacier avalanche that destroyed the town of Batten in Switzerland — where nearly all inhabitants were evacuated — a lack of early warning systems in the Himalayas left locals and tourists at the mercy of flash floods.    

How much is climate change to blame? 

The causes of glacier collapse are part of a complex web of interrelated changes to high mountain landscapes due in part to rising global temperatures, say scientists.   

Levan Tielidze, research fellow in Glacial Geomorphology at Australia's Monash University, says the Himalayas are not, as is often imagined, a "frozen and relatively stable environment," but "dynamic systems in which glaciers, snow, permafrost, rock slopes, rivers and monsoon processes interact." 

"As the climate warms, these components are changing simultaneously, meaning hazards can cascade from one process into another," he tells DW.  When rock, ice and water interact in more unpredictable ways on the world's highest peaks, the resulting debris flows "can transform into a catastrophic flood far downstream."  

Almost 25 years ago, in what was then the biggest glacial collapse in history, one glacier crashed onto another in the Caucases Mountains of North Ossetia in the Russian Federation. The event caused avalanches of ice and debris that slid more than 24km (15 miles) and killed around 125 people.  

"The Kolka Glacier disaster was one of the early warnings of the increasing occurrence and potential severity of such glacier-related hazards," Tielidze tells DW. 

Meanwhile the UN says glaciers in Nepalese mountains have declined by one-third in 30 years, which has added to their instability. 

Some research suggests that even if emissions from burning fossil fuels were low enough to prevent the planet from heating by more than 2 degrees Celsius (36 degrees Fahrenheit) compared to pre-industrial times, the wider Hindu Kush Himalayan region could lose up to half its glacier cover — compared to 2020 levels — by the end of the century.  

For Dipesh Chapagain, senior scientist at the United Nations University Institute for Environment and Human Security, there is "ample scientific evidence linking greenhouse gas emissions to global climate change, which in turn is driving glacier retreat, permafrost thaw and ice avalanches."   

"These changes are increasing both the frequency and intensity of climate-related disasters in mountain regions," he adds.  

Chapagain has studied hundreds of glacial lake outburst floods (GLOFs) in the Hindu Kush Himalaya region — caused when meltwater from glaciers and snow creates a lake that eventually bursts and sends extreme flash floods downstream. The number of these events per decade has increased fivefold since the 1950s.  

The glacier collapse in Nepal and Tibet shares similarities to a GLOF event. However, the former was very different as it skipped the "intermediate lake-formation stage entirely … and directly triggered the flash flood," says Chapagain.  

The avalanche also generated seismic activity equivalent to about magnitude 5.2 before the momentum of the water-rich debris flow that entered the river system saw it travel roughly 100 kilometres, notes Tielidze.  

"These hazards are becoming so difficult to classify," he adds, in reference to the way mountain rock, ice and water are interacting in more unpredictable ways due to climate change.   

Is it possible to adapt to more extreme glacier collapse impacts? 

The 2025 glacial collapse in the Swiss Alps that destroyed the entire village of Blattan resulted in one fatality. Detailed surveillance of glacier deformation and the surrounding terrain allowed authorities to evacuate the population before the catastrophic collapse. 

But this is less possible in the Hindu Kush Himalaya, which contains more than 63,700 glaciers, notes Tielidze. 

"In the Himalayas, we need to move beyond monitoring only individual dangerous lakes," he says.  

 "We need integrated systems combining satellite observations, seismic detection, glacier and slope monitoring, river gauges, weather forecasts and automated warnings."  

For rapidly evolving events such as the Nepal disaster, detecting seismic movement could give downstream communities "precious minutes of warning." 

Chapagain says the transboundary nature of glacial hazards in the Himalayas makes "cross-border and regional cooperation on disaster preparedness" just as urgent as early-warning systems. 

However, currently available adaptation technology and capacity may be insufficient to "respond to a disaster on the scale we've just witnessed on the Bhotekoshi River in Nepal." 

"What we have learned from this is we can adapt to climate change but not to climate apocalypse," says Shreya K.C., the Kathmandu-based advocacy working group co-coordinator of the Loss and Damage Youth Coalition, in a statement.  

A rapid reduction in planet-heating emissions that are at driving glacial melt and instability will need to accompany any adaptation measures. 

"We cannot engineer our way out of unlimited warming," says Tielidze. "Some mountain hazards will remain unpredictable and some changes will eventually exceed the capacity of communities and infrastructure to adapt."

Edited by: Tamsin Walker