The geomorphologist Ludovic Ravanel explained on franceinfo this Friday the conditions of the collapse of a mountain section in Switzerland, “within a hair’s breadth” of the village of Brienz.
Ludovic Ravanel, geomorphologist, research director at the CNRS at the Edytem laboratory in Savoie, deciphers on franceinfo Friday June 16 what happened during the collapse of a mountain section near the village of Brienz in Switzerland, the last night. “We cannot directly blame global warming”he points out.
>> Global warming : the mountains on high alert
Franceinfo: Do we know what caused the Brienz landslide?
Ludovic Ravanel: Its occurrence has been expected for tens, even hundreds of years. This site is extremely unstable, covering almost three square kilometres. We have an environment of 100 to 200 million cubic meters moving on this site. This movement is related to the geological structure. And on these alpine valleys that were covered in ice during the last glacial periods, the glacier created what is called a decompression which decompressed the slopes, which prepared these great instabilities. Then all you have to do is add a little water to the land, and this is particularly the case in spring, when the snow melts, so that everything goes away.
Is there a link with global warming?
The link is not direct at these altitudes. Higher in altitude, beyond 2,500 or 3,000 meters above sea level, there is a problem of permafrost, that is to say the thawing of permanently frozen ground. In the case of this landslide, the crest of the rocky sector that has destabilized is between 1,500 and 1,700 meters above sea level, that is to say that it is not frozen at all. In any case, it has thawed for a very long time. We cannot therefore directly incriminate global warming, unlike many other phenomena. For example, a few days ago, not far away in Austria, about 100,000 cubic meters of rock fell. And there, for once, the link with global warming is direct. But in the case of Brienz, it’s not direct.
Elsewhere in the Alps, this phenomenon is at work. For what ? Is it because the ice acts like a glue?
Absolutely. At high altitude and in the Alps, we still have many sectors that exceed 3,000, 3,500, even 4,000 m in altitude, where we have what is called permafrost. These are permanently frozen terrains, which we know well at high latitudes, but which we also have at high altitudes. This permafrost allows the presence of ice in the cracks, it is an ice which is several thousand years old and which today has a role of cement. We are talking about ice concrete or ice cement.
With climate change, this cement of ice is thawing deeper and deeper. And we are witnessing both an increase in the frequency of rock destabilizations – which we will generally call landslides, collapses – and then an increase in volumes. Still not far from Davos, at the end of the scorching summer of 2017, more than three million cubic meters fell; therefore even more important than what fell last night. This created a mudslide of almost six kilometers which arrived at the level of the village of Bondoun. Nearly one hundred buildings were destroyed or badly damaged.
The mountain changes face. Is this a new danger that needs to be taken into account?
Yes, there are indeed new dangers that are emerging in the high mountains. This is also what is called at the ministerial level “ROGP”, risks of glacial and periglacial origin. The Ministry of the Environment has developed an action plan in relation to these issues which affect rock faces, but also glaciers. At the level of these glaciers, we have a whole series of new risks, with pockets of water which are draining, glaciers which are destabilizing.
“Generally speaking, at high altitude in the Alps, there are many new processes that can carry risks, both for mountaineers, but also for infrastructures, and even valleys”.
Ludovic Ravanel, geomorphologistfranceinfo
In the long term, should we imagine closing certain sectors in the mountains?
Temporary and local closures are not at all excluded. Today, the awareness of mountaineers and hikers is improving. On their own, they are likely to avoid the most dangerous places. In the summer of 2022, when we had absolutely terrible conditions in the high mountains, we observed a relatively low accident rate because the mountaineers knew how to manage themselves, based on the knowledge more widely disseminated.