For my son's 7th birthday party he wanted a volcano cake. So I obliged. The bottom layer was a 11x15x2 sheet cake (chocolate) split with a layer of chocolate icing in between layers. I also baked a 10" round an 8" round and a 6" round cake. I cut a hole in each of the round cakes big enough to fit a tall plastic drinking cup.
I stacked the 3 round cakes (with chocolate icing between) on top of the sheet cake in the top-left corner of the sheet cake. I used the cake I cut out to make room for the cup as the small hill in the front-left side of the cake. I used bamboo skewers around the cup as well as a couple more through the layers of cake in the volcano for support.
I iced the entire cake over with whipped chocolate icing. making sure I built a rim of icing around the top of the volcano except in 1 spot where i wanted the lava to flow.
The "beach" area I cut away half a layer of the sheet cake and put some "sand" (brown sugar, nilla wafers and graham crackers crushed together) in it, followed by blue writing gel icing. I slowly transitioned from "sand" to "rocks (crushed Butterfingers and chocolate sprinkles) as i got closer to the volcano. I covered the volcano and hill in the largest chunks of "rocks", letting them fall off naturally and build small piles of "rubble" at the base of the volcano and hill.
I used more "sand" to form the dinosaur next and tic-tacs for eggs. I used cinnamon sticks as my palm trees with Italian parsley for the leaves (had to be placed right before the party). I used green colored icing and a grass tip to make a grass border and write out happy birthday. I added some dinosaur party favors, including 1 partially submerged IN the water, 2 guarding their "nest" of eggs, 1 pteranadon in the lip of the volcano, 1 pteranadon "flying" on a piece of floral wire stuck to one of the skewers, and a couple more dinos lounging around.
To make the eruption, I added dry ice to the cup I put in the center of the volcano. I made "lava" out of marshmallow fluff slightly diluted with a tiny amount of hot water and a karo clear corn syrup. Colored red and brown to make it look more like lava then poured into the cup with the dry ice.
After we sang happy birthday, I added a cup of hot water. It started smoking violently. After the violent smoking stopped, it was still boiling so it started forming bubbles in the marshmallow fluff that built up and soon spilled over the edge.
The cake was a hit, we had employees taking pictures and kids from other birthday parties coming to take a look.