“If we don’t limit global warming, rock falls will multiply” – Liberation

How beautiful the mountain is. However, it sometimes threatens to collapse. In Switzerland, in Brienz, a small village in the canton of Graubünden, the risk is such that the town must be completely evacuated. A hundred inhabitants are called upon to leave the premises by this Friday, May 12, as they have become too dangerous. The “Insel”, a volume of rocks of 2 million cubic meters overlooking the village, is moving so quickly that it will collapse within one to three weeks. Impossible to predict, for the moment, the extent of the damage that will result.

In 2017, still in the canton of Grisons, a section of the Piz Cengalo mountain collapsed and caused a mudslide in the village of Bondo. Eight people are still missing. Phenomena of this type are not new but are on the increase. Michel Jaboyedoff, a geology graduate and professor at the University of Lausanne, is a specialist in environmental risk management. He comes back for Release on the acceleration of the phenomenon of landslides in the Alps and the role of climate change in this regard.

Concretely, what is happening in Brienz?

Historically, this area is constantly moving. A whole side of the mountain, and up to the summit, has moved and is still moving. It’s all happening very slowly, but now the pace is picking up. Until a few years ago, the village of Brienz moved horizontally by half a meter per year. At the moment, it’s one meter per year! In the heart of the village, many houses are splitting and weakening. But what worries the authorities is what is happening above: 2 million cubic meters of rock could come off the mountain. If it lets go in one piece, it could reach the village and have serious repercussions.

A landslide is a rock mass that dismantles and rolls lower. Some come close to falling individual blocks, which fall and spread with rebounds. Others, more severe, are called rock avalanches. They carry a lot more rocks and descend much further into the valley. The most important rock avalanche in Europe took place in France, in 1248: Mont Granier killed a thousand people and buried an entire village. In Brienz there is a much higher chance that it will fall apart and not hit the village, but you can never guarantee that. Let’s say there is a 1 in 10 chance that everything will go off at the same time and trigger a rock avalanche. And the canton of Graubünden does not want to take this risk.

This same canton was the scene in 2017 of a landslide from Piz Cengalo. The Federal Office for the Environment in Switzerland has acknowledged climate change as the cause. Is this the case for Brienz?

What is certain is that it is a rocky region of very poor quality. In Brienz, I think that the melting of the snow is an important factor: a lot of water infiltrates this rock which is constantly moving and therefore it creates cracks… With colleagues from Grenoble, we have shown that intense rains were the main cause of rock falls. But heat, due to climate change, also plays an important role.

For thousands of years, ice formed. This work generated instability and destabilized the rock, as it takes up space. For the moment, the ice acts like a glue, but if it melts, the rock no longer holds. And we can see that the more time passes, the hotter and drier the summers. So areas, previously permanently frozen, are no longer so during the summer period. The water that results from the melting of the ice slips into the rock cracks and leads to overpressures of water on the rock.

This means that, for example, Mont-Blanc is experiencing increasing rockfall activity, leading to its closure last summer. The phenomenon is spreading throughout the Alps. If by chance we do not limit global warming, rock falls will multiply and will take place at higher altitudes.

Could this multiplication of risks lead to the closure of certain mountain areas, in order to avoid tragedies?

Yes. Here, two components must be taken into account. First, there is the hazard: falling rocks and rock avalanches. If there is nobody, there is no risk. The risk increases because more and more people practice the mountains. So the question of responsibility arises, given the increase in tourists in certain areas. If it is discovered in an area that rockfall is increasing, yes, the authorities could have to prohibit access to risky pedestrian paths.

But I don’t know if it’s sustainable. Many climbers have a much higher risk acceptance than us. They put themselves in danger more easily and some people are likely to say “we assume this responsibility”, and if a tragedy occurs, it is the mountain rescue police who will go to save them.

Are there solutions to constrain a landslide, or at least prevent it more effectively?

In France, you have Risk Prevention Plans (PPR) with risk analyses. We in Switzerland have also drawn up maps to say “here it’s dangerous, there it isn’t”, but we haven’t carried out a very elaborate risk analysis. As we have money, we protect ourselves with that: we place a lot of nets to protect the roads, for example.

In Brienz, they were reactive because the region is prone to landslides. They are monitoring the movement of the rock with radar, as they had not taken the correct measurements at the time. [lors de l’effondrement du Piz Cengalo, ndlr]. They had closed the area, but not strictly, so the eight missing were probably hikers passing by. Afterwards, if someone had asked me if there was going to be a rock avalanche there, I wouldn’t have been able to predict it.

To constrain landslides, some specialists are considering digging galleries under landslides. The goal is to drill vertically in order to make the water flow from the rock mass and avoid overpressure and slow down the movement of the rocks. Some opt for dykes, and that’s a good idea, but beware of the measures taken behind them. If an area considered risky is then protected by a dike, the occupation of the territory could increase, therefore the danger also increases. If a landslide occurs and is not contained, the risk may end up exceeding the pre-existing one.