I did this as warm up project for value with my Art II (9th graders). And my students loooved it. Furthermore, my Art I's asked if they got to do that this year:-) I stole the idea from Mr. E's art blog. This project is a great project that can be stopped and started anytime!
He has more detailed instruction on his site- so check it out!
* I couldn't think of a name for this, and I kept calling it different things, so finally I just let my students name it- and Dr. Suess Tornado Worms is what I got.
* Note- I was being lazy and didn't bother to rotate the photos- they should be verticle in orientation.