Movies persistently depict quicksand as vicious threat, as deadly, consuming Mother Nature, sucking you down into her belly never to return to the living.

Of course, it's easier to drown in a bowl of chicken soup than in quicksand.  Quicksand is buoyant.  Actually that's a gross understatement.  In that photo, I'm hanging on to a very large rock which I hoped would get me deep enough to get just my head on the surface.  Keturah helped by standing on my shoulders to push me  down, but by the time she could step back to take the picture...well, you can see how much I floated up in those few seconds.

The buoyant (upward) force is equal to the weight of the volume displaced.  Quicksand is about twice as dense as a human body, which is about as dense as water.  That means that in quicksand, like that on the banks of the Colorado, you will you sink about to your waist.  Sinking deeper requires a lot of effort and some clever strategy.

Hollywood strikes out again in the action against pseudoscience.

Yes, but do you really believe what I just said?  Would you risk drowning as I did?  Is Archimedes' principle something with "buzz-saw certainty"?  Are the odds of surviving (I did!) as good as the odds, say, of the state lottery taking away your money in the long run (if you play)?

What, do  you  think?