Underwater avalanches go with the flow

Lubricating fluid changes how grains collapse

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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.

GO WITH THE FLOW An avalanche involving fluid between its grains (top sequence of snapshots in time) unfolds in a more complex manner than a dry avalanche (bottom sequence).