Mountains are among the planet’s most beautiful places. They’re also becoming the deadliest

Jan Beutel was half-watching a live stream of Kleines Nesthorn, a mountain peak in the Swiss Alps, when he realized its cacophony of creaks and rumbles was getting louder. He dropped his work, turned up the sound and found himself unable to look away. “The whole screen exploded,” he said. Beutel, a computer engineer specializing in mountain monitoring, had just witnessed a glacier collapse. On May 28, an avalanche of millions of tons of ice and rock barreled down the slope, burying Blatten, a centuries-old village nestled in the valley below. Local authorities had already evacuated the village after parts of the mountain had crumbled onto the glacier; a 64-year old man believed to have stayed remains missing. But no one expected an event of this magnitude. Successive rock avalanches onto the glacier increased the pressure on the ice, causing it to melt faster and the glacier to accelerate, eventually destabilizing it and pushing it from its bed. The collapse was sudden, violent and catastrophic. “This one just left no moment to catch a breath,” Beutel said. The underlying causes will take time to unravel. A collapse of this magnitude would have been set in motion by geological factors going back decades at least, said Matthias Huss, a glaciologist at the Swiss university ETH Zürich. But it’s “likely climate change is involved,” he said, as warming temperatures melt the ice that holds mountains together. It’s a problem affecting mountains across the planet. People have long been fascinated with mountains for their dramatic beauty. Some make their homes beneath them — around 1 billion live in mountain communities — others are drawn by adventure, the challenge of conquering peaks. These majestic landscapes have always been dangerous, but as the world warms, they are becoming much more unpredictable and much deadlier. “We do not fully understand the hazard at the moment, nor how the dangers are changing with climate change,” said David Petley, an Earth scientist at the University of Hull in England. Snowy and icy mountains are inherently sensitive to climate change. Very high mountains are etched with fractures filled with ice — called permafrost — which glues them together. As the permafrost thaws, mountains can become destabilized. “We are seeing more large rock slope collapses in many mountains as a result,” Petley told CNN. Glaciers are also melting at a terrifyingly rapid rate, especially in regions such as the Alps and the Andes, which face the possibility of a glacier-free future. As these rivers of ancient ice disappear, they expose mountain faces, causing more rocks to fall. There have been several big collapses in the Alps in recent years as ice melts and permafrost thaws. In July 2022, about 64,000 tons of water, rock and ice broke off from the Marmolada Glacier in northern Italy after unusually hot weather caused massive melting. The subsequent ice avalanche killed 11 people hiking a popular trail. In 2023, the peak of Fluchthorn, a mountain on the border between Switzerland and Austria, collapsed as permafrost thawed, sending more than 100,000 cubic meters of rock into the valley below. “This really seems to be something new. There seems to be a trend in such big events in high mountain areas,” Huss said. Melting glaciers can also form lakes, which can become so full that they burst their banks, sending water and debris cascading down mountainsides. In 2023, a permafrost landslide caused a large glacial lake in Sikkim, India, to break its banks, causing a catastrophic deluge that killed at least 55 people. Last year, a glacial lake outburst caused destructive flooding in Juneau, Alaska — a now regular occurrence for the city. After two years in a row of destructive glacial flooding, Juneau is scrambling to erect temporary flood barriers ahead of the next melting season, the Anchorage Daily News reported this week. As well as melting ice, there’s another hazard destabilizing mountains: rain. Extreme precipitation is increasingly falling on mountains as rain instead of snow, said Mohammed Ombadi, an assistant professor at the University of Michigan College of Engineering. His research shows every 1 degree Celsius of global warming increases extreme rainfall events by 15%. This pushes up the risks of flooding, landslides and soil erosion. Northern Hemisphere mountains will become “hotspots” for extreme rain, Ombadi said. Heavy rainfall this month in Sikkim, a Himalayan state in northern India, triggered a series of landslides, killing at least three people. Images show deep muddy scars carved into the mountain, with buildings and trees obliterated. Scientists do have tools to monitor mountains and warn communities. “There are fantastic instruments that can predict quite accurately when a rock mass (or) ice mass is going to come down,” Huss said. The difficulty is knowing where to look when a landscape is constantly changing in unpredictable ways. “This is what climate change actually does… there are more new and previously unrecognized situations,” Huss said. These are particularly hard to deal with in developing countries, which don’t have the resources for extensive monitoring. Scientists say the only way to reduce the impact of the climate crisis on mountains is to bring down global temperatures, but some changes are already locked in. “Even if we manage to stabilize the climate right now, (glaciers) will continue to retreat significantly,” Huss said. Almost 40% of the world’s glaciers are already doomed, according to a new study. “We could have maybe avoided most of (the negative impacts) if we had acted 50 years ago and brought down CO2 emissions. But we failed,” Huss added. The consequences are hitting as the numbers of people living in and visiting mountains increases. “We’re just more exposed than we used to be,” he said. Ludovic Ravanel, an Alpine climber and geomorphologist who focuses on mountains’ response to global warming, has a front line view of the increasing dangers of these landscapes. Mountains are the “most convincing” hotspots of climate change, he told CNN. When he’s focused on the science, he keeps his emotions at arm’s length. But as a father, and a mountaineer, it hits him. “I see just how critical the situation is. And even then, we’re only at the very beginning.”