Soil liquefaction occurs during earthquakes, causing a quicksand-like bog which can topple buildings and swallow cars.

Liquefaction occurred during the recent Christchurch earthquake
Videos of the 2011 Christchurch earthquake liquefaction can be found here (during) and here (aftermath).
I got the idea for a soil liquefaction demonstration from the brilliant ASTA resources for the Year 9 plate tectonics unit. The instructions for the demonstration are in Lesson 4 on Earthquakes.
It worked very well. There are before and after shots below, and then a video.
Left: Before the earthquake. The building stands tall. Right: The building has collapsed, and is half submerged.
August 28, 2013 at 11:51 am
Looks fantastic Rogan! I imagine that it would really help the students to visualise what can happen. Did they seem to respond to it well?
August 28, 2013 at 9:51 pm
Thanks Chris. They expected it to fall over, but liked that it became semi-submerged, too.
I am putting together a motorised shake table earthquake simulator for testing foam buildings, as well. Will use an eccentric weight, similar to the units used to make mobile phones vibrate. Watch this space.