Heat Waves Are Thawing the Permafrost Holding Mont Blanc Together, Scientists Say

Record heat waves in Europe this summer have accelerated the collapse of the Mont Blanc massif on the France-Italy border. Permafrost that has held its rock faces together for thousands of years is thawing, triggering a surge in rock falls, researchers and residents say. A rock-prone gully long used by climbers ascending the 4,805-metre summit became temporarily impassable after a succession of heat waves caused defrosting cliffs to come apart.

On the nearby Aiguille du Midi peak, at 3,842 metres, the average July temperature has risen from 1.6°C in 1994 to a record 3.3°C this July, according to Meteo France, the national weather service. "The mountain really dried out, with temperatures unlike any I had ever experienced," said Stephane Bozon, a deputy mayor in Chamonix-Mont-Blanc who is in charge of the town's safety. "From mid-July onward, we saw an increase in rock falls, with crevasses opening up and rock collapses making some areas difficult to reach or traverse."

Permafrost acts like cement holding steep Alpine rock faces together, and this year's heat waves have weakened it significantly. "As the ice changes, we have seen a huge, huge number of rock falls and rock collapses this year," said Ludovic Ravanel, a researcher at Savoie Mont Blanc University who studies climate change's effects on mountain snow, glaciers and frost. A collapse is defined as a rock fall of more than 100 cubic metres — enough to fill a large shipping container — and Ravanel expects this year's tally in the Mont Blanc massif to reach around 400, roughly ten times the number two decades ago and above the previous high of nearly 300 in 2022.

In Italy, Alpine glaciers in the Lombardy region have lost more than 40% of their surface area since 1991, according to the region's glacier service. "While it used to snow at high altitudes in the past, now it rains," said Vanda Bonardo, head of the Italian branch of the International Commission for the Protection of the Alps, adding that this has also affected the stability of the terrain.

The Aug. 26 floods that swept through Nepal and China were triggered after a collapse of bedrock and glacier ice sent debris and water surging through multiple Himalayan rivers; initial assessments by scientists found that climate change played a key role in creating the conditions for the disaster.