Liquifaction

Liquifaction is a made up word, but the process is totally real. If you find some sand that is saturated with water (think shores of the ocean, or on a river bank in a low lying area) you can jump on it. Go up and down a bunch of times and continue jumping while keeping your feet over the same spot each time. Pretty soon, you'll feel the ground start to get soft, and jiggle, and then, you'll sink into it!

It's the closest thing to quicksand that you'll find this side of the Sahara and it's tons of fun...that is, until you can't get out and the tide starts coming in.