On the Matterhorn, an international research team led by Jan Beutel from the Department of Computer Science shows how meltwater in permafrost can lead to rock slope instability. A rock pillar collapsed there in 2023 after years of water ingress. Long-term measurements and models now illustrate how meltwater leads to rock slope instabilities and rockslides - a consequence of climate change.
For many years, Jan Beutel and colleagues have been operating sensor networks in high mountain areas: for example, he has established a wireless sensor network on the Hörnligrat ridge of the Matterhorn that collects temperature, movement, and seismic data in an extremely steep permafrost terrain. This approach makes it possible to establish the "laboratory outside of the laboratory" on real mountain slopes: Real-time data, combined with innovative sensor technology, forms the basis for instability models. "With our expertise in wireless sensor networks and high-alpine environmental monitoring, we are bringing a technological approach to natural hazard research that significantly expands high-mountain research, including on the Matterhorn," says Jan Beutel from the Department of Computer Science .
Water makes rock unstable
When meltwater penetrates rock crevices in permafrost, it transports heat deep underground, where it causes the frozen rock to thaw further. Jan Beutel has worked with researchers from SLF Davos, RWTH Aachen, and TU Munich to investigate the processes that destabilize the rock to the point of collapse using a high-profile example: on 13 June 2023, a free-standing rock pillar collapsed on the Hörnligrat, the most prominent access route to the Matterhorn. Around 20 cubic meters of rock fell; fortunately, nobody was injured. For years, water had been seeping into the rock below the pillar during snowmelt, temporarily thawing and weakening the rock and so gradually destabilizing it. "Climate change is accelerating such processes, which are now a common driving force behind the increasing frequency of rockfalls in high alpine permafrost", says SLF researcher Samuel Weber.
Chain reaction in the rock
The researchers observed and measured the rock pillar for nine years. Their most important piece of equipment in this work was a GNSS receiver. With its help, the researchers were able to record every movement of the pillar down to the millimeter. They compared this measurement series with seismic signals, time-lapse images and laser recordings, among other things. Using rock samples taken from the Hörnligrat as a basis, they studied the rock pillar in a laboratory as part of an international project. "Permafrost thaw significantly reduces the critical angle of friction at which a rock mass starts to move", explains Weber. The findings were transferred to a computer model. This was a success, as the simulation reproduced the measured movements on the Matterhorn one-to-one.
Three effects are exacerbating instability. Due to climate change, the ice in the permafrost that had previously sealed the rock is melting. This allows water to penetrate deeper, putting pressure on the rock. At the same time, meltwater transports warmer temperatures deep underground. This is a chain reaction, because it causes the permafrost and ice to thaw even faster - which in turn allows the water and thus the heat to penetrate even deeper. "This also reduces friction at the fracture point by up to 50 per cent, which further weakens the rock", says Weber.
This video provides deeper insights into the work of the researchers, their methods and findings, as well as details of the processes triggered by meltwater in permafrost.(Video: Samuel Weber / SLF / Stimme: murf.ai)
Ten days before the collapse
The interplay of these effects was made visible in a spectacular way on the Hörnligrat. The rock pillar had been slowly tilting for years, with this process speeding up from 2022 onwards. "Time-lapse photography documents a visible acceleration in the ten days before the final collapse in June 2023", says Weber. At the same time, three seismometers in the vicinity provided evidence of the dynamics of the impending collapse. "Weather data and temperatures in the permafrost indicate that infiltrating water caused rapid, short-term thawing underground and played a major role in the event", clarifies Weber.
With a view to better assessing the risk of rockslides in permafrost, Beutel wants to learn more about the interaction between temperature, water and ice in frozen rock and its mechanical effects. To do this, he needs more data. "We're now focusing on the role of water especially in very steep
Publication: Progressive destabilization of a freestanding rock pillar in permafrost on the Matterhorn (Swiss Alps): Hydro-mechanical modeling and analysis. Samuel Weber, Jan Beutel, Michael Dietze, Alexander Bast, Robert Kenner, Marcia Phillips, Johannes Leinauer, Simon Mühlbauer, Felix Pfluger, and Michael Krautblatter. Earth Surface Dynamics 2025 DOI: 10.5194/esurf-13-1157-2025
