Rockfall Geological causes of rockfalls in Brienz GR

The rockfalls in Brienz GR are due to geological factors and are not linked to climate change. Geologists explain the causes and history of the landslides.

The rockfalls above the Grisons mountain village of Brienz are the result of geological processes and not climate change. Geologists point out that the movements are caused by a combination of water and certain types of rock in the ground.

Once again, Brienz GR has had to be evacuated due to the threat of a rock avalanche. All residents are to leave the village by midday on Sunday, possibly for several months. 1.2 million cubic meters of debris threaten to bury the village. In June 2023, a similar stream of debris came to a standstill just a few meters from the village.

Geologist Stefan Schneider emphasizes that the debris avalanches, rockfalls and landslides in Brienz GR are not linked to climate change. These events have a long history dating back to 1878. "With the best will in the world, I can't imagine a connection," he told the Keystone-SDA news agency.

Historical landslides

The first documented debris flow occurred in 1878, when large masses of rock slid at a speed of four meters per day to the right above the village. The flow was in motion for a year and a half before it stopped 100 meters from the village.

Since then, there have been repeated major and minor rockfalls and numerous boulder falls. The subsoil of the village has also always been in motion.

Schneider suspects that the snowy winter of 1999 may have influenced the movements. When the large amounts of snow melted, a lot of additional water seeped into the ground, which, in combination with the geological conditions, is a dangerous mixture.

Geological conditions

The high plateau on which Brienz GR lies consists of Grisons slate and flysch, a very soft type of rock. When water is added, the result is a greasy slurry, explains Schneider.

This mixture and the inclination of the rock cause the mountain above Brienz and the entire village to slide downhill. The mountain moves 2.5 meters a year, while the scree above the village is currently slipping around 20 centimetres a day.

No influence of climate change

Although the scree slope reacts to precipitation, this is not responsible for all the movements in the area, according to Schneider. The increased precipitation associated with climate change also has no direct impact on the slide speeds.

Rather, longer periods of extreme weather, such as very wet summers or snowy winters, are noticeable. However, these are not necessarily due to climate change.

Thawing permafrost also has no effect in Brienz GR, as the village is too low at around 1100 meters. Permafrost only occurs at altitudes above 2300 meters.

According to Schneider, there are many landslides in Graubünden like the one in Brienz. However, it is not yet clear why the events in the mountain village in the Albula Valley have come to such a head.

SDA