An intense summer heatwave across Europe has triggered a record number of rockfalls in the Alps, creating a deadly environment for climbers.
Scientists say the exceptionally hot weather has destabilised mountain faces, with popular routes on Mont Blanc and the Matterhorn suffering the worst effects. Mont Blanc, the highest peak in the Alps, rises on the border between France and Italy, while the Matterhorn stands on the Swiss and Italian border.
The rockfalls have already killed three climbers on Mont Blanc with the climbing season barely underway. The deaths prompted local authorities to close mountain lodges on the most common route to the summit.
A new analysis predicts the Mont Blanc massif will see 450 rockfalls this year. The previous record stood at 300 rockfalls in a year, set in 2022 when another severe heatwave hit the Alps.
Dr Ludovic Ravanel of the French National Centre for Scientific Research said: "That is an absolutely staggering figure, given that just 10 or 20 years ago, there were only a few dozen."
"A large majority [of the rockfalls] can be attributed to the climate crisis," he added.
Temperature records broken
The severe heatwave gripping Europe has broken temperature records across the continent.
The Basel and Binningen region of Switzerland recorded a high of 39.7C (103.5F), which is the hottest temperature ever measured in the northern Alps.
In the popular French climbing region of Chamonix, which sits at the base of Mont Blanc, temperatures have regularly climbed above 30C (86F).
The heat has critically impacted the zero-degree isotherm, the altitude above which the temperature drops below freezing. This boundary normally sits between 11,480 and 13,120 feet (3,500 to 4,000 metres) during summer.
During July, parts of the Alps saw this freezing point pushed 4,600 feet (1,400 metres) higher than normal.
Combined with exceptional levels of drought, the high temperatures have left the mountainous rock faces of the Alps at their least stable point on record.
Melting permafrost and glaciers
The structural integrity of the mountains depends heavily on ice. Dr Ravanel said "invisible" ice has been lodged in the cracks between rocks for several thousand years, where it "acts as a kind of cement holding the mountains together".
As temperatures rise above zero, this permafrost melts and releases the rocks. At the same time, high temperatures cause glaciers to retreat and lose thickness, removing the stabilising pressure that had held the rock wall in place.
This has culminated in a record-breaking season of rockfalls all across the Alps. Popular mountains like Mont Blanc and the Matterhorn have been particularly badly affected.
In July, two Czech climbers were killed in a rockfall on Mont Blanc while crossing the notorious Couloir de Gouter. The steep rock gully is widely known as the "Death Couloir" due to its history of accidents. Between 1990 and 2017, the couloir was the scene of 347 rescues, including 102 fatalities and 230 injuries.
The Czech team attempted to cross this section before dawn when the rocks were more stable, but conditions are currently so bad that even these precautions were not enough.
Another climber, a 31-year-old man, was also killed by a rockfall in August while climbing in the Mont Blanc area.
Hut closures and warnings
Last week, Jean-Marc Peillex, mayor of the Saint Gervais district that governs the French side of Mont Blanc, ordered the closure of two popular mountain huts on the most common route to the summit.
With the climbing season key to the local tourist economy, this is an extreme measure that has not been taken since the 2022 summer heatwave.
Mr Peillex told Explorers Web: "It is up to all climbers, whether accompanied by guides or not, to fully grasp the gravity of the situation and abandon their climbing plans for the duration of this crisis."
"Climbing Mont Blanc is not a challenge or a feat of daring, and it is not worth risking the lives of climbers and rescuers out of pride," he said.
Even if conditions cool later in the season, this summer's extreme heat is likely to make climbing treacherous for the rest of the year.
Dr Ravanel said: "Even if the surface freezes over again, the enormous amount of heat from the summer of 2026 will continue to penetrate the ground until November, December, or even as late as January."
He predicts that the "biggest rockfalls" are expected in autumn, but that these will be less frequent.
Despite this, Dr Ravanel does not believe that access to the high mountain regions of the Alps should be restricted, describing them as "above all, a place of freedom".
He added: "The mountaineering community regulates itself [and] does not put itself at greater risk during a heat wave than during a cooler summer."
