There are two basic type of explosion I would like to render. Here they are. I would incorporate some element of one into another, like if I choose to go for the undewater big bang, I' have to add if not flames an intense glow beneath the water. Also I love the concept of the tiny little ship standin on front of it.

Any idea regarding the material to be used for the "mushroom" cloud ...?

Also I would ask if it effective to use a geometry like mushroom to fill with aforedmentioned mat, or its best to try metaballs or a series of spheres...