A couple of months ago a video of the necco wafer/coca cola volcano was popular on the internet. Explanations were scarce. Here's the answer: nucleation. ie. In any gas saturated solution (coca cola) the gas tends to separate out on the sides of the container. If one places a sponge shaped solid in the liquid (necco wafers). the gas may separate out so fast that a veritable eruption occurs. I think the video showed it spurting 10 feet into the air.