This is one of the coolest things I have ever seen on a job. The dirt was literally moving in waves as you can see. Be sure to watch in HD for the best picture.

What this is, is someone filled in an old in ground swimming pool with clay and didn't punch a hole in the bottom to let any surface or rain water escape, so over time the clay became extremely saturated. When I drove the mini excavator over it the clay began to "pump" or liquify and this is what happened. I have seen soil liquefaction before but never to this extreme.