this has been floating around facebook a lot lately so thought i would share here. some really neat things happen to the sand as the frequency is increased.
Thanks for the link John, very interesting. I wonder if crop circles are a more complex pattern done in a similar way.
One of the comment has it right. The patterns are caused by standing waves. When the vibrations traveling through the media intersect sometimes they result in the peaks and sometimes troughs and the sand (salt?) aligns to these. Standing waves also explains Bose audio technology.