One of the biggest risks of winter ski tours away from secured slopes are certainly outgoing snow slabs, which can grow into avalanches and sweep people away. According to a computer simulation, these avalanches could occur in a similar way to certain earthquakes. This is what Johan Gaume from the École Polytechnique Fédérale de Lausanne and his research group write in Nature Physics.
For their study, the team ran hundreds of simulations over days to model how large masses of snow loosen and then rush to the valley. The focus was on snowboard avalanches, which most often lead to fatal accidents. In the process, a layer of snow loosens up on the slope and begins to slide down quickly, taking further layers of snow with it. The snowboards often break off when a load acts on them from above; the crack along the edge of the break can propagate at up to 300 kilometers per hour.
Usually a weak, less solidified and porous layer of snow collapses below a harder, heavier location, which then slips above this surface. It starts slowly at first, but after a few meters the gravity ensures tensions in the compact layer of snow, which ultimately lets it break into smaller parts: the avalanche picks up speed. These simulations compared Gaume and Co with the video of an avalanche that the snowboarder Mat Schaer started, a former student of Gaume. The analysis of the film then confirmed the simulation.
A similar process also occurs in earthquakes that occur during lateral plate displacements. Here, a daughter crack can form in front of the main fracture front and spread at high speed, while paving the way for the large rock fracture. Gaume and his team hope that their study will help improve avalanche prediction. As a result, zones in the Alps, for example, in which these avalanches primarily occur, could be identified more precisely.
