Now this is pretty cool. Quicksand has long been a popular device in movies as a dangerous peril for heroes or a means of comeuppance for bad guys, but the quicksand of reality doesn’t come close to what you see on the screen. Most folks know by now that the danger from quicksand is greatly exaggerated and we’ve all heard the sage advice that, should you happen to find yourself in quicksand, the best thing to do is not panic as you’re more likely to float than sink. The guys at MythBusters even did an episode where they whipped up a batch of quicksand to see how dangerous it is and found that it was damn near impossible to force themselves under the surface.
Yet Hollywood continues to try and milk the concept by coming up with new twists on it. In 2002’s The Scorpion King starring The Rock, for example, our hero lures the bad guys into a desert cave filled with “dry quicksand” that swallows them up in a matter of seconds! I recall letting out a derisive snort when I saw that scene for the first time. I may have even uttered a “yeah right, as if” as well. Super fast dry quicksand? How silly is that? Well, it may not be as silly as I thought:
Sand supports weight. Force chains are known to play a prominent role therein. We considerably weaken the force chain structure by letting air flow through very fine sand. Even when the air is turned off and the bed has settled, the prepared sand does not support weight: Balls sink into the sand up to five diameters deep. We call this state of sand dry quick sand. The state is not to be confused with the normal quick sand which is a mixture of sand, clay, and water. The final depth the ball reaches scales linearly with its mass and above a threshold mass, a sand jet is formed which shoots sand straight and violently into the air.
The high speed video captures on the site are amazing to watch even if there’s not a a lot of explanation of the how and why to be found. They appear to have saved that for the Nature article. There’s also nothing that talks about how likely these conditions are to crop up in the real-world, though I’d hazard a guess that it’d be a rare occurrence at best. These experiments are on a fairly small scale and it’d be interesting to see if they could be replicated with bigger objects. Still, it’s clearly possible that dry quicksand could exist given the right conditions. At the very least this should make it a little easier to suspend one’s disbelief the next time Hollywood trots out this common plot device.
Found via Boing Boing.