Spectacular rockfalls in the Alps more frequent as mountain permafrost melts
A 100-tonne rock crashes from the side of a French mountain and falls hundreds of metres to the valley below. Images of a spectacular rockslide on the Col de l'Encrenaz in the French Alps spread on social media and TV channels on September 10th. It followed a series of similar falls on the other side of the Chamonix valley, in the famous Mont Blanc massif. Experts say that such events have become more frequent in recent years because rising temperatures are gradually melting permafrost high in the French Alps.
Issued on:
August 7th, August 22nd, August 27th, August 30th, August 31st. Through the month of August, mountaineering pages on social media have been flooded with videos showing rockslides in the Alps, especially in the Mont Blanc massif, the range that includes Europe’s highest peak, at 4810 metres.
And then on September 10th, a tourist captured an even more spectacular video. Between 30,000 and 40,000 m3 of rock rolled down the peaks of the Aiguilles Rouges in an area that isn’t usually subject to rockfalls. Due to its location and size, experts say the rockfall could be the biggest in the Aiguilles Rouges in recorded history. “The only known instance of such a large rockfall in the Aiguilles Rouges was an event that happened 10,000 years ago,” geomorphologist Ludovic Ravanel told FRANCE 24. “There may have been others but they weren’t recorded or haven’t been detected.”
Four rockslides on the Aiguille du Midi
At least four major rockslides were filmed on a single mountain in August: the Aiguille du Midi, famous for the cable car that takes tourists to its 3842-metre summit from the town of Chamonix in the valley.
Numerous videos taken from the Chamonix area show rocks falling away from the mountain summit complex, which includes a viewing platform, a snack bar and a gift shop. The cable car is the highest vertical-ascent cable car in the world.
"The Aiguille du Midi cable car is on borrowed time," one tourist can be heard saying on the video of a rockfall on August 30th, 2024.
‘The spots where the rockfalls occur aren't usually in the most heavily-trafficked’
Olivier Greber, a guide and president of the Compagnie des Guides of Chamonix, witnesses rockslides regularly.
These things don't happen every day, but near the Aiguille du Midi there have been quite a few significant rockfalls. Clients are always very, very surprised because they're not used to seeing this.
You hear a big noise on the north face. Try to visualise it: generally all you see is a cloud of dust. Then the last boulders roll down, and the cloud finally dissipates. Given the amount of dust, it's often hard to get an idea of the volume.
The spots where the rockfalls occur aren't usually in the most heavily-trafficked. But rockfalls still affect the way we guides do our jobs with climbing clients. But for tourists who want to visit the Aiguille du Midi using the cable car, for example, it has very little impact.
These events are potentially dangerous. After all, these are large volumes of rock that break away from mountain walls. Mountains have always been dangerous.
We try to pay close attention to warning signs: the sight or sound of sand or water running off the mountainside for instance. When we see these signs, we stay clear from these areas.
To limit risks, mountaineers and guides adapt to new conditions
Statistics from the PGHM [France’s mountain police, the Peloton de Gendarmerie de Haute Montagne] show that rescue operations from rockfalls have not increased in recent years. It has been around 2% of all rescues for years. It shows that mountaineers are adapting well to changing conditions.
Being a guide means you must be sensitive to these changes. We have to find ways to keep the mountains accessible, and adopt different ways of climbing them if necessary.
We adapt to changes in the seasons too. If we want to do mixed climbing [climbing on snow and rock] or snow routes, we do it in the spring. We also adapt geographically, which means that we go to areas where there's no permafrost: the Aiguilles Rouges, Colombière and the Prealps [lower ranges west of the Alps].
There are also places that used to be classic routes that we can no longer visit. We may have to postpone climbing certain routes, such as the Arête des Cosmiques, or in the Couloir du Gouter which gives access to Mont Blanc. We don’t forbid climbers to go there, but we plan ascents at certain times on certain routes.
We might also go back to the origins of the profession, when guides very often had a second activity. More and more guides have a second job nowadays.
‘It happens when summers are very hot’
Ludovic Ravanel is a geomorphologist at CNRS, France’s national center for scientific research. In 2007, he set up an observation network in the Mont Blanc massif to keep track of these landslides. While climate change has contributed to an increase in the number of events in recent years, he says that 2024 has not so far been an especially bad year.
Above 2500m on the north face of Mont Blanc and 3000m on the south face, walls are permanently frozen. This thermal state, called permafrost, allows ice to form in the cracks. The ice is thousands of years old and acts as a cement. If it melts, that's when we see destabilisation. It happens when summers are very hot.
In 2022, we reached an all-time high with almost 300 events over 100 m3. This year, there has been less destabilisation. There was a lot of snow this winter, which stabilised the ground. Although temperatures have been relatively high on average this summer, there haven't been heat waves like in 2022 or 2023. We don't yet have a precise figure, but we're looking at 150 to 200 rockfalls in 2024.
As for the dangers for tourists visiting the Aiguille du Midi, Ravanel is unconcerned.
The sector below the Aiguille du Midi is relatively active. And the area is also highly visible, so it's not surprising that we see and hear a lot about them.
In the middle section, the rock is highly fractured and located in an altitudinal range that is favourable to the permafrost melting. The permafrost is deteriorating, and summers are getting drier and hotter, so the ice cover holding the rock together is also shrinking.
The Aiguille du Midi cable car was installed in the 1950s. It was a good idea to build the platform high on the mountain. From a safety point of view, it's good: at the summit, the permafrost temperature is very low and the whole thing is stable.
Tourists going up to the Aiguille du Midi does not destabilise it. There is absolutely no direct impact from tourism, apart from the fact that tourists’ travel emits greenhouse gases.
Tourists may be safe, but the valley could be at risk
However, Ravanel points out the risks of these increasingly frequent events.
It's dangerous, yes. But mountaineers are particularly careful. Guides are adapting too.
The problem is that we are beginning to see phenomena that can produce risks all the way down to the valleys. These are known as glacial and periglacial hazards.
In 2017, in the Swiss canton of Grisons, 3.1 million m³ of Piz Cengalo broke off and fell onto a glacier. The glacier was pulverised and turned into water. The water mixed with the rock, causing a series of mudflows that reached the village of Bondo, 6km away. Around a hundred buildings were destroyed, and eight hikers were killed.