Place the open side of the paper drinking cup you will use face down on the top (dome side) of the bowl cake. Cut around the edge, through the cake to remove a round circle of cake. NOTE: Do this gently as you will be using this piece for the top of the volcano.
Place the bowl cake on top of the Bundt cake, flat side against the rounded top of the Bundt cake, aligning the openings in the middle of each.
Place the paper drinking cup into the top of the bowl cake, making the opening of the cup flush with the top opening of the bowl cake. The cake opening should hold the cup snugly.
Using a serrated knife, ‘carve’ the sides of the cake so the sides form more of a smooth line (like a mountain). NOTE: My Bundt pan has many indentations as you can see and I wanted to minimize that look. Carved pieces may be inserted in between the two cakes (under the bottom of the bowl cake, on top of the Bundt cake) to form a cake ‘shim’ (an angled piece that fills the gap). This will stabilize the cakes, and fill the gaps before frosting.
Using an apple corer, make a hole all the way through the ‘top of the volcano’ (the cake piece you removed from the bowl cake). Place the top of volcano piece on a small plate.
Once in the shape you like, frost with the chocolate frosting. I used a spreader and made downward wave-like texture. Carefully frost the separate top of the volcano piece as well.
Drizzle the different color glazes down the cake, making the affect of lava. Do the same on the volcano top.
Sprinkle with Pop Rocks if you choose to do so for both the base cake and top.
Place the separate top only in the freezer. Leave in the freezer for at least 30 minutes. This will ensure it's firm before placing on the top of the volcano.