Why the Brienz rockslide occurred later than initially expected
Keystone-SDA
A pile of debris is thought to have delayed the rockslide in the Swiss village of Brienz in June 2023 by several weeks.
The debris at the foot of the unstable slope slowed down the sliding rock masses, thereby making it more difficult to predict when the collapse would occur.
This is shown by a study carried out by researchers at the WSL Institute for Snow and Avalanche Research (SLF), which was published in the latest issue of the journal Engineering Geology.
“This example highlights the limitations of current approaches to predicting when such an event will occur,” said study leader Robert Kennerin a press release.
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As early as March 2023, an unstable section of rock above the village had been moving at an increasingly rapid pace. Experts therefore anticipated a collapse would occur soon. Brienz was evacuated on May 12. However, it was not until the night of June 15 to 16 that around 1.2 million cubic metres of rock and debris came loose. The mass narrowly missed the village.
Predictions were difficult
The reason for the delay lay in a debris slope at the foot of the unstable rock face. The rock mass pushed its way into the debris, which initially slowed its movement.
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However, this braking effect repeatedly weakened. New slip planes formed within the debris pile, allowing the rock mass to move faster once again. As a result, phases of stronger and weaker acceleration alternated.
“It was therefore virtually impossible to make accurate predictions as to when the slope would fail,” explained Kenner.
It was not until the morning of June 15 that the situation changed. The western part of the unstable rock mass broke away. The eastern part then came to a standstill, whilst the remaining rock mass accelerated sharply and flowed down the valley as a debris flow late that evening.
The situation in Brienz has since eased considerably. After more than a year of evacuation, residents were allowed to return to their homes at the end of January 2026.
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Translated from German, reviewed by an English Department journalist.
