The winter blanket of snow covering the Alps is stunningly beautiful– and incredibly dangerous. In 2004-2005, 26 people died in avalanches in Switzerland alone. The victims range from occasional snow-boarders catching some powder off-piste to backcountry ski guides with years of experience. In this mountainous country, avalanches also pose a serious public danger. They can bury people in their homes, cut off access roads or even flatten whole villages. Scientists have put great effort into trying to understand the physical mechanisms at work in avalanches, particularly in the domain of fluid mechanics, in an attempt to improve our ability to predict and manage avalanche danger. But progress is limited because the computer models that simulate complex fluid movement are still quite rudimentary.
EPFL professor Christophe Ancey, an expert in rheology, or flow phenomena, is working to improve that situation. His team is building an installation that will generate avalanches in the comfort of the laboratory. Unlike natural avalanches, no two of which are alike, and all of which are quite uncomfortable in scale and force, all the variables involved in these slides can be controlled and the same avalanche can be studied repeatedly. The simulation data will be used to construct a new numerical model capable of describing the avalanche’s dynamic behavior.
The laboratory system Ancey is developing is based on the “dam-break” concept, in which a viscous fluid is poured onto a steeply inclined plane. The blue ooze flowing down the slope may not look like snow, but it deforms in the same way an avalanche does, and shares the same physics – the highly complex, non-equilibrium, non-linear flow that is characteristic of heavy snow and mud. “No existing numerical model can reproduce what’s happening in even this simple setup,” explains Ancey. “As a first step, we need to be able to reproduce what we observe, and with a model that takes only hours, not days, to run.”
Christophe Ancey | alfa
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