2023-09-01 12:11:00
They were believed to be eternal, immutable, since the rock is said to be so solid. Yet even our granite giants are reeling under the weight of climate change. For a little over thirty years, the walls of the Alpine peaks have been crumbling. Until sometimes collapsing in an impressive din and clouds of dust. And the phenomenon is accelerating. The cause is the global rise in greenhouse gas emissions. “It heats up way too fast. The erosion of the mountains is normal, but not at this rate”, exposes the glaciologist Ludovic Ravanel on this hot and sunny August 17, on the famous terrace of Montenvers which overlooks Chamonix (Haute-Savoie) and reveals a part of the Mont-Blanc massif.
Last year, due to an abnormally dry winter and a scorching summer, 300 rockfalls were observed on this mountain range alone. A terrible record: on average “there are more than a hundred a year” specifies the researcher. This year, the rocks have not stopped falling. And the late heat wave these days, which is drying up the high mountains, is making the situation worse. At the Cosmiques ridge, a popular climb for mountaineers where the mercury exceeded 10°C at the start of the week, this sad spectacle has become commonplace. In the front row: the Cosmiques refuge, perched at 3,613 meters. “There was another landslide in mid-August,” reports Anna Bernicot, one of his two caretakers.
Human activities threaten the balance of a system essential to climate regulation
The memory of the 2005 collapse
At times, 300 to 400 cubic meters of rock collapse at once, as in August 2018 and 2022. Fortunately, the wooden cabin is located “on the other side of the collapses. But we don’t know how long the refuge will last before being swept away, surely not long”, she projects. This week, the Cosmiques itinerary has been suspended for security reasons. And further south, in the Ecrins massif, the access path to the Sélé and Pelvoux refuges was closed to the public following a landslide in the Pélas Verney corridor which occurred on Monday August 21. In the future, “we expect an increase in the frequency of rockfalls”, resumes “Ludo”, the nickname of the glaciologist. From the balcony of Montenvers, packed with tourists, he points to the Aiguille du Tacul: “It’s one of the peaks that evolves the fastest because it is very fractured. It is in the altitude range, between 3,200 and 3,500 meters, which is most affected by the degradation of permafrost.”
A legacy of ancient ice ages, permafrost refers to soils whose temperature remains below 0°C for at least two consecutive years. This thermal state allows the presence of ice in the hollow of the cracks of the rock, formed via the infiltration of rainwater or snow. It is called ice cement: “As long as it is present, it ensures a certain cohesion. But when it melts, the mountain no longer holds”, summarizes Ludovic Ravanel.
According to the glaciologist, one of five experts on the subject in France, over the past decade, some of the peaks encircling Mont-Blanc, like the Aiguille du Midi, have taken “between 1 and 1.5° C more. It is enormous”. Consequence: their destabilization has greatly accelerated. “It exploded around 2000. And since 2010, it’s exponential in terms of frequency and volume,” explains the man who compared hundreds of photographs of the massif dating from the mid-19th century to the present day.
Accelerated melting of Antarctica: the oceans would be impacted “for centuries”
The year 2005 remains etched in the memory of the valley: entire walls fell off the formidable Bonatti pillar, a race reserved for the most daring mountaineers. With the 800,000 tonnes of granite – ie 4 to 5 times the volume of the Arc de Triomphe – a piece of “alpinism’s heritage has departed. It’s like watching Notre-Dame burn for Parisians,” said Mathieu Tisné, head of natural risk management at the community of municipalities. Five years ago, the collapse of the Trident du Tacul also made climbers shudder. “Mountaineers considered it one of the healthiest areas of the massif. Even the specialists were surprised”, abounds Ludovic Ravanel.
Ski resorts under threat
Beyond history, it is a whole practice that is turned upside down. As the “ice concrete” evaporates, the mountainous terrain becomes unstable and dangerous. Also, for two to three years, the community of mountaineers “adapts” confirms the president of the Compagnie des guides de Chamonix, Olivier Greber. “Mixed Races [itinéraires mêlant roche, neige et glace] are shifting: before it was during the summer holidays, now it’s May, June and the beginning of July.” Even if, this year, the mild temperatures made it possible to hike and climb until mid-August.
Refuges and ski resorts are also closely monitoring the situation. According to Ludovic Ravanel, 947 high mountain infrastructures, fifty years old, are threatened by the instability of mountainous soils. “Permafrost is also present at the level of what are called superficial formations: heaps of stones, scree, moraines… And on these, we have built pylons, ski lifts. With the melting, all the high altitude stations have problems”, he assures. Under these conditions, adapting often means consolidating facilities. Or build the foundations at a depth of regarding twenty meters in order to find healthier rock, under the first icy and weakened layers.
But in the valley, all our interlocutors repeat it: they remain “humble” in the face of this changing, unpredictable nature. Especially since the study of mountain erosion, delicate given the extremely complex geological history of the observed terrain, has only existed since the beginning of the century. “We don’t know everything, and therefore only know a few things”, judges Mathieu Tisné. And since reality is one step ahead of expertise, the erosion is much faster than scientific forecasts.
Lack of snow: how can ski resorts survive?
Thus, scientists, mountain guides, associations, rescuers, refuge guards, mountaineers or even local elected officials, join forces to understand and analyze this new risk in the mountains. For now, their best assets remain communication, awareness and prevention. Proof that it is effective, the number of accidents related to landslides has not increased. But at present, no village is under surveillance: “We are pushing everyone to become our eyes because researchers cannot be everywhere”, insists Ludovic Ravanel.
“What will happen when the warming has thawed the first layers of the mountains?” asks Claude Jacot, the mountain safety assistant for the town of Chamonix. And “Ludo” to answer: “Not all of them will collapse. Many are stable. On the other hand, those that are fragile risk triggering big events. And from this point of view, the landscapes will evolve in the coming decades.” Surely leaving unrecognizable Alps in 2100.
1693577660
#Climate #change #Chamonix #mountain #longer #holds
