Don't blow your top! OK, do but do it in a not too messy manner!
Loaded up the workbox with the ingredients we needed to make his volcano blow (we got this while traveling-at the Cracker Barrel Store, but you can find them in all sorts of places-it is the easy way to make a volcano)...and included the Magic School Bus video on Volcanoes. The Janice VanCleave's Volcanoes book is a great resource. We did the volcano experiment using a potato cork-but couldn't get pics b/cuz it blew before we could position the camera and snap one of it. It was OK, not super exciting but it demonstrated the pressure build up in volcanoes nicely.