Europe's record-breaking summer heatwave has triggered a surge in rockfalls across the Alps, creating a deadly hazard for climbers and forcing authorities to close routes on popular peaks like Mont Blanc. Scientists warn that rising temperatures are destabilizing the mountains by melting ancient permafrost that acts as a natural cement.
In the Mont Blanc massif alone, the number of rockfalls is projected to reach 450 this year, significantly exceeding the previous record of 300 set in 2022. Dr. Ludovic Ravanel of the French National Centre for Scientific Research stated that while only a few dozen rockfalls were recorded a couple of decades ago, a large majority of the current incidents can be attributed to the climate crisis.
The intense heatwave has pushed the 'zero-degree isotherm'—the altitude above which temperatures drop below freezing—up to 1,400 meters (4,600 feet) higher than normal in some alpine regions. This, combined with drought conditions, has left rock faces in a critically unstable state. "Invisible" ice, which has held rocks together in cracks for millennia, is melting, causing rocks to loosen and fall. Additionally, receding glaciers are losing their ability to provide stabilizing pressure on rock walls.
The dangerous conditions have already led to fatalities. In July, two Czech climbers were killed by a rockfall in Mont Blanc's notorious Couloir de Gouter, often referred to as the 'Death Couloir.' Another climber died in August in the same area. In response to these incidents, the mayor of Saint Gervais, the municipality governing the French side of Mont Blanc, ordered the closure of two mountain huts along the most frequented route to the summit. This measure, last implemented during the 2022 heatwave, highlights the severity of the situation.
Temperatures across Europe have shattered records, with Basel, Switzerland, registering 39.7°C (103.5°F), the hottest temperature ever recorded in the northern Alps. Climbing hubs like Chamonix have frequently seen temperatures exceed 30°C (86°F).
Even as temperatures potentially cool later in the season, the lingering heat from summer is expected to affect the mountains. Dr. Ravanel cautioned that heat absorbed by the ground could continue to penetrate until late December or even January, potentially leading to more rockfalls in the autumn, though likely less frequently. Despite the increased risks, some, like Dr. Ravanel, believe that access to high mountain regions, considered places of freedom, should not be restricted, trusting the mountaineering community to self-regulate risk.