The physics of avalanches is similar to that of earthquakes

Snowboarder Matthew Shire. Credit: Rudy Floyk

Scientists from EPFL and the WSL Institute for Snow and Avalanche Research (SLF) have gained deeper insight into how avalanches form, paving the way for more effective risk assessment measures for these catastrophic events that cause more avalanches and deaths each year than other types of avalanches.

The team of EPFL and SLF scientists has made a breakthrough discovery that could significantly affect their field of research. By scaling the avalanche simulation from a meter to a hundred metres, they gained a better understanding of the mechanisms behind these events. Their discovery also demonstrates the benefits that advances in computer processing power can bring to methods used to observe complex physical phenomena. The team’s findings appear in the journal Nature Physics.

Their work is based on a 2018 study by EPFL professor Johann Gaum and UCLA scientists. That preliminary study, published in Nature Communications, describes a 3D simulation method the researchers developed to model avalanches with unparalleled accuracy. Gaume is currently the chair of EPFL’s Snow and Avalanche Simulation Laboratory (SLAB), within the EPFL School of Architecture, Civil and Environmental Engineering (ENAC), an affiliate of the SLF Institute. He and Ph.D. Student Bertil Trout took the study even further by applying it more widely – and made a surprising discovery. They find that the way the cracks propagate changes during the slab’s avalanche release process. For example, they note that crack propagation velocities exceed 100 meters per second, which exceeds velocities of about 30 meters per second typically measured in experiments. The two scientists initially thought that they had made a mistake.

Avalanche video analytics. Credit: Tetouan Besir

Ultra crack spread

Avalanches are characterized by a sharp and wide fracture line that occurs at the top of the released snow mass. This avalanche forms when a dense layer of snow (slate) sits on top of a weak layer of snow with little cohesion. When an avalanche is triggered, for example by a skater, the weak layer collapses and the slab loses its primary support structure. Post bending of plates is one of the main drivers of crack propagation. At least that was the mechanism suggested by experiments and numerical models so far, based on tested and simulated plates less than two meters in length.

But by modeling slabs measuring about 100 metres, EPFL and SLF scientists found that once crack propagation extends beyond about three to five metres, slab tension becomes the only driver of the release process, causing the weak layer under shear to fail. This phenomenon is similar to the so-called “supershear” rupture mechanism observed in the rare high-magnitude earthquakes reported so far. “We felt we were on our way to something important, but we needed empirical data to confirm it,” Gaume says.

Video Analytics

Then a series of coincidences gave Trottet and Gaume a chance to confirm their discovery. First, Gaume attended a presentation at the conference in which Ron Simenhois of the Colorado Avalanche Information Center described the high-tech video analysis method he’s working on. Around the same time, Matthew Scheer—a former environmental engineering student at EPFL who is now a professional snowboarder and engineer at MétéoSuisse—sent Gaume a video showing how he barely survived a major avalanche.

“The avalanche occurred at Col du Cou in the Swiss Alps,” says Gaume. “We had data on snow at the event, and Schaer’s video was of excellent quality because he was filming snowboarding. By analyzing the video and examining various parameters, we were able to confirm our model results for the first time.” In total, four real-world avalanches allowed Scientists have confirmed the transition from the “anti-fracture” mode to the “supershear” mode that has been reported during some large earthquakes. Based on these findings, the SLF Institute is now developing large-scale facilities in Davos in order to gain more insights into the avalanche triggering process.

Towards a better risk assessment

Their work will help ice researchers come up with new assumptions that can simplify computer models of avalanches and greatly shorten the computing time required – from several days to just a few minutes. Improved models can be used to quantify, for example, avalanches, which is important information for effective risk prediction and management.

Towards better avalanche predictions More information: Bertil Trottet et al, Transition from quasi-Rayleigh cracking to super-slit propagation in avalanches, Nature Physics (2022). DOI: 10.1038/s41567-022-01662-4 Submitted by Ecole Polytechnique Federale de Lausanne

Quote: Avalanche physics similar to that of earthquakes (2022, July 26) Retrieved on July 26, 2022 from https://phys.org/news/2022-07-physics-slab-avalanches-similar-earthquakes.html

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