Landslide Cantonal geologist sees danger for Blatten not completely averted
Guillaume Favre-Bulle has been head of the Natural Hazards Service of the canton of Valais since October 1, 2025. The natural disaster in Blatten VS dominates the daily life of the new cantonal geologist, as the mountain could once again provide unpleasant surprises.
28.01.2026, 04:30
SDA
Eight months ago, on May 28, 2025, the 44-year-old Favre-Bulle witnessed the glacier collapse and subsequent landslide on the Kleine Nesthorn above Blatten at first hand. "When the glacier broke off, I was looking at the webcam and was aware that there was a lot going on in the area," he says. "Suddenly I saw the landslide start. I jumped up from my chair. The worst-case scenario had become reality before my eyes."
The successor to the retired Raphaël Mayoraz as cantonal geologist has a master's degree in environmental geosciences from the University of Lausanne and worked in geology and engineering offices for 15 years before moving to the canton of Valais in 2017. In 2022, he became head of the Department of Geological Hazards and Mineral Resources within the Cantonal Natural Hazards Service.
Risk still exists
After the natural disaster, the main task for the department was to secure the resulting lake for the winter and assess the hazards below and above the deposit. At the same time, an updated hazard map was drawn up. In the meantime, 70 percent of the destroyed village is in the red zone. According to Favre-Bulle, the costs for the work subsidized by the department currently amount to around CHF 20 million for Blatten.
Even if ten million cubic meters of boulders, debris and ice have fallen on the Lötschental village by 2025, the mountain could still cause surprises. "One million cubic meters could still fall from the Kleiner Nesthorn overnight*, explains Guillaume Favre-Bulle.
Priority monitoring of the area is therefore still necessary. In addition, further landslides or debris flows could occur. These would lead to an increase in the current surface area of the lake.
Five years to melt the ice
Around 3 million cubic meters of ice are still trapped in the sediment mass, according to the cantonal geologist. They are melting very slowly. "We will try to create large trenches to drain all the water from the deposit. According to experts, this could take around five years," says Favre-Bulle.
Ultimately, this area, which can no longer be used as building land, could be reopened for agriculture. The canton of Valais is currently considering this possibility.
According to the cantonal geologist, it would be ideal for the coming months if the River Lonza were to remain in its current bed "and we would only have to monitor the phenomenon of erosion. This would require a summer without any major storms," explains the geologist.
Further events are imminent
Valais has been hit by severe storms several times since 2024. In addition to Blatten, these include the overflowing of the Rhone in the Sierre region (June 2024) and the dozens of debris flows near Lourtier (2024-2025). The increasing number of these incisive events is worrying the population.
"This will be one of my major challenges, along with the consequences of global warming," confirms Guillaume Favre-Bulle. Even if existing buildings unfortunately cannot always be protected, there are measures in place to keep the population safe, such as evacuations. It is important that the population does not expose itself to any danger, does not approach an ongoing natural event and does not drive in the event of an exceptional storm.
Currently, 150 locations in Valais are being monitored to prevent major disasters. According to Guillaume Favre-Bulle, however, there are natural events that cannot be predicted or controlled, such as a boulder falling on a vehicle. The increasingly frequent and violent thunderstorms also pose a danger.
Important ongoing projects
In December, the Valais Grand Council rejected the creation of nine additional full-time positions at the cantonal department for natural hazards. According to the cantonal geologist, this means that certain projects have to be prioritized.
In addition to Blatten and the work on the third Rhone correction, the most important projects of the Natural Hazards Office are the design of the Dranse in Martigny (over 30 million), the work on the Vièze in Monthey (around 20 million), the Navizence in Anniviers (40 million) and the Baltschiederbach (23 million). These will be realized over several years at a cost of 2 to 4 million per year.
