Mountains are collapsing: A Swiss mountain peak fell apart, sending 3.5 million cubic feet of rock into the valley below. Scientists warn climate change could make more mountains crumble.

• Mt. Fluchthorn’s tallest peak, on the Swiss-Austrian border, collapsed in June.
• Experts say peaks in the European Alps and Southern Alps of New Zealand are at risk of collapse, too.
• The damage and dangers from mountain collapse disproportionately impact indigenous communities.

On June 11, the main peak of Mt. Fluchthorn, on the border of Austria and Switzerland, collapsed without warning.

Roughly 3.5 million cubic feet of earth tumbled down, filling the valley below with 40 Olympic swimming pools’ worth of rocks, mud, and dirt, LiveScience reported. While no people got hurt, a religious cross marking the summit was destroyed.

Fluchthorn had three peaks, and the main, southern one used to be the tallest. With the south peak collapsed, the middle peak is the new summit at 11,145 feet — the second-highest summit in the Silvretta Alps.

Overall, Mt. Fluchthorn is 60 feet shorter than it was earlier this year, per LiveScience.

The problem with permafrost

Why did the peak collapse? Well, like many mountains in the far north, Fluchthorn had a lot of permafrost — a permanent layer of ice and dirt under the mountain’s surface.

“Permafrost is important because frozen water within the ground holds the ground surface together and prevents it from moving. But when that ice melts, the liquid water can flow away. The ground surface becomes less stable and can move, often very quickly,” said Jasper Knight, a geoscientist at the University of Witwatersrand in South Africa.

When a big chunk of mountain moves quickly, like with the mudslide at Fluchthorn, that’s called a mass movement.

“Global warming is causing the permafrost to melt, which is the trigger for these mass movement events to take place,” Knight said.

Across the world, mountains with permafrost melt have shown larger and more frequent landslides, the Intergovernmental Panel on Climate Change reported. Research on rockfalls in the Alps suggests summer heat waves are a common trigger for melting permafrost.

But warming temperatures due to climate change affect more than permafrost. The surface layer of ice and snow can melt, too, and cause flooding and mudslides. Melting glaciers can also cause mass movements, when mountains lose the ice that was propping up its sides for years on end, per the IPCC.

Which mountains are at risk?

Scientists have a hard time predicting when a specific mountain will have its next landslide or rockfall. But they can track global patterns and determine which mountain ranges have more risk.

Mass movements are most common in steep mountains where glaciers are rapidly retreating, Knight said. Mountains meeting those criteria are particularly common in the European Alps and the Southern Alps of New Zealand, he added.

When a mass movement occurs, others are likely to follow.

“As mountains get smaller, they reduce pressure on the surrounding slopes, and this is often the trigger for mass movements,” Knight said.

Knight added that sometimes rock falls and landslides can buttress a mountain’s base and make it more stable. But they usually make a mountain’s slope more sensitive to environmental changes. A mountain like Fluchthorn that has had mass movements in the past is more likely to have them again.

The human element

Across the globe, over 670 million people live in high-mountain areas, per the IPCC. Climate change puts their lives in danger from mudslides, landslides, rockfalls, and more.

Mass movements can also increase the risk of blocked roads, damaged farmland, and mercury contamination in local bodies of water. These dangers disproportionately impact indigenous communities.

Human behavior can make a mountain more or less sensitive to climate change. Insider spoke with Alejandro Argumedo and Tammy Stenner from Asociación ANDES (Peru), an organization that protects biodiversity in the Andes while advocating for indigenous rights.

Argumedo and Stenner said Andean indigenous peoples have an in-depth system of traditional knowledge to predict and cope with extreme weather conditions on the mountainside.

One strategy they use are agricultural terraces — step-like tiers of farmland set along the mountain’s slope — that  “prevent soil erosion and landslides,” Argumedo said.

He added that for the terrace strategy to work, the top of the mountain needs natural pasture and native tree species to act as sponges for extra water. The Stone Village in Yunnan, China, has successfully practiced a similar water management system for 1,300 years.

But these techniques only work when they’re used. Argumedo and Stenner said the Peruvian government has refused to recognize or invest in traditional ecology management strategies.

“Landslides happen because mountain ecosystems are degraded and terraces are abandoned,” Argumedo said. He added that mining and road building have further destabilized the mountain environments.

The future

As climate change accelerates, mountain environments change more quickly, as well. Knight predicts mass movements will become more common in the next decade.

But the situation isn’t hopeless. Scientists believe if we work now to slow down climate change and prevent mountain degradation, we can still stop the worst outcomes from happening and help protect the planet’s mountains and the communities that live near them.