For the volcano, I made Cocoa Krispie treats and shaped them around a narrow mouth cup. I tried two different size volcanoes. On the actual cake, I went with the larger volcano. There is a slightly larger cup that the treats are molded to in the larger volcano. Then I put a narrow tall shot glass plastic cup inside of the larger cup. This made for filling with dry ice and water a lot easier because I could do that outside of the volcano and then place the shot glass cup in its spot without dripping water on the volcano. And I could add more dry ice and warm water when I wanted to make the eruption again.