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Snowboarders and marine engineers both worry about avalanches, but the latter may have a tougher job when working underwater. They have to understand not only what makes a cliffside collapse, but also how fluid between sand grains affects the flow.
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Physicists have now simulated how that process happens. A team led by Farhang Radjai of the University of Montpellier in France developed calculations for how particles flow when they collapse from a tall stack. Different simulations tackled particles that were dry, that were wet as if with water, or that were immersed in a stickier, more viscous liquid.
Having water in the mix, the scientists found, means that the grains collapse more slowly at first than in a dry avalanche. But as the landslide continues to fall, the fluid helps lubricate the grains and keeps them moving along. In the end, surprisingly, the dry avalanche and the wet avalanche traveled about as far, just in different ways. The viscous flow stopped much shorter.