Climate change: which glaciers are considered “potentially dangerous” in France?

Protect and protect yourself from glaciers. Traveling to Chamonix, in Haute-Savoie, the Minister of Ecological Transition, Agnès Pannier-Runacher, detailed the government's policy to safeguard these giants and their ecosystems, but also anticipate the dangers that their melting may pose to populations. . Measures taken as part of the National Plan for Adaptation to Climate Change (PNACC) (new window) which aims to prepare France to live under +4°C.

The stakes are high. The Alps and Pyrenees are particularly vulnerable to climate change, with temperatures there having already increased by 2°C in the 20th century, compared to +1.4°C in the rest of France. Concerning glaciers, their warming is even estimated at +3°C. According to scientists, these giants have lost 25% of their surface area in half a century and could disappear by 2100. (new window).

Taconnaz: a cold glacier that warms up

A melting of the ice which is not without consequences for the populations who live near these threatened giants, in particular due to “the creation of lakes and pockets of underground water which can suddenly rupture and flow into the valley”, detailed Agnès Pannier-Runacher. “The glaciers that we monitor are mainly in the Alps, details for TF1info Ludovic Ravanel, glaciologist and researcher at the CNRS. Because in the Pyrenees, there's not much left (new window). But it is a list that evolves from one year to the next. One year, glaciers can be a concern, then the following year, if we talk about glacial lakes, they are no longer a problem, it is very evolving.”

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However, some are considered particularly sensitive. This is the case of the Taconnaz glacier, in the Chamonix valley, in Haute-Savoie. “It is a very large glacier which dominates a large avalanche corridor which reaches into the valley”, explains Ludovic Ravanel. The site is particularly sensitive in the event of destabilization. “This glacier is a cold today, explains Olivier Gagliardini, researcher at the Institute of Environmental Geosciences (IGE). And we observe that it is warming and that within 20 to 30 years, it could be destabilized. The whole question is how? And how big could the blocks of ice be that will break off? We must anticipate this risk for the populations below.”

Les Bossons: a retreating glacier

The Bossons glacier, still in the Chamonix valley, is also under surveillance. An alert was launched last year for this site. “The lake located slightly on the right bank at the front of the Bossons glacier has been drained. It was developing since 2918/2019 (new window) and last year, given its volume and the risk it posed, it was artificially drained”, explains Ludovic Ravanel. An operation which seems to have borne fruit, today the lake does not seem to be reforming.

But the giant poses another problem: its retreat destabilizes it. “We have a problem on the front of the glacier. It is well positioned today on slopes that are not too steep, but in a few years, with melting, it will find itself on steeper slopes, with a risk of collapse from the lower part of the glacier, we are trying to anticipate the danger that this may represent in the valley. explained Olivier Gagliardini.

Tignes: the danger of the Rosolin glacier

The problem of the Bossons glacial lake is also found on the Rosolin glacier, in Tignes, “but bigger”explains the IGE scientist. “We have a lake which is blocked by a glacial dam. The risk is that water will intrude between the glacier and the rocky base and carry the water towards the town of Val-Clarée below. If water finds its way under the glacier, this can cause a situation similar to that of Deux Alpes in 2018, where a lake was formed and drained within a few hours, resulting in significant lava torrential. Fortunately, this area was completely wild.says Olivier Gagliardini.

Tête-Rousse and Bonne Pierre: significant disasters

The Tête-Rousse glacier is also still carefully monitored by scientists, even though in 1892 it dumped thousands of cubic meters on the village of Saint-Gervais. (new window). “We still have a water problem inside the glacier,” explains Olivier Gagliardini. A situation due to its particular composition: a cold front and a high temperate which causes a flow of water in the small expanse of ice located at more than 3000 meters above sea level.

Glacier known for the disaster caused last June, that of Bonne Pierre is also heavily monitored. In spring, under the combined effect of heavy rains on the snow cover and the draining of a hidden lake of nearly 100,000 m³ under the glacier, large quantities of water ravaged the valley, devastating the hamlet of the Berarde (new window).

“The glaciers are bearing the brunt of the climate change (new window)with large quantities of water that can be stored in these expanses of ice. If the water is held close to the interior of the glacier, they are very difficult to observe, we do not see them on the surface or by satellite observations. explained Olivier Gagliardini. “We now have glaciers above 4,000 meters in altitude which are experiencing melting that they had never experienced before, and all this water finds itself blocked inside the glacier if it is cold, it accumulates in crevices and as the water is heavier than the ice, it ends up exerting forces which cause the ice, at one point, to no longer resist. This is surely what happened. during the Marmolada disaster (new window) in Italy”, explains the scientist again.

An effective action plan

“The problem is that we are in a transitional phase where the glaciers are being brutalized with unprecedented temperature increases for these ecosystems,” underlines Olivier Gagliardini. With a danger: not being able to anticipate the rapid formation of certain glacial lakes or pockets of water. “The pockets of water that really pose problems are those that are not necessarily perceptible before they form”summarizes Ludovic Ravanel.

In the coming decades, it is estimated that up to 80 glacial lakes could form in the Alps, all of which pose no threat to populations. This is particularly the case under the Mer de Glace and the Argentière glacier, towards Chamonix which could see the appearance “basins which will be able to produce sometimes very large lakes”, describes Ludovic Ravanel. Pockets of water which, however, benefit from significant monitoring in France. “We are fortunate to have an action plan on glacial risks that has been initiated and is working,” reassures Olivier Gagliardini.