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Now we know why landslides can flow like rivers

Engadget Engadget 6/04/2016 Daniel Cooper
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The rule of thumb with a landslide is that however far up a mountain it begins, you're safe if you can get twice that distance away. So, if a fall begins a mile up, you need to be two miles away before busting out the popcorn and beers. Except, that's not really true, since plenty of landslides travel far longer distances than that, causing serious harm to people and property nearby. Thanks to Brown University's Brandon Johnson, we know why: it's because the falling rocks hitting the ground can create a set of very specific vibrations. These vibrations reduce the amount of friction in the local area, causing landslides to flow like rivers.

Interestingly, the theory of Acoustic Fluidization has actually been knocking around since 1979. It was originally offered up by Jay Melosh, who worked out the math to help explain this form of natural disaster. Unfortunately there was no way to prove the hypothesis correct back in the day since the computing power simply wasn't there. These days, it was pretty easy to run the simulations necessary to determine of acoustic fluidization was the cause. Don't bust out the booze to celebrate just yet, however, since the study has also established that these long-running landslides can occur anywhere.

American Geophysical Union, Paper (.PDF)

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