How about 3 Dimensional Short-Time Decals of Earth and Stone beeing ripped appart by Bertha, Nuke or ComExplosions? They could appear at that point where the expanding Explosion"bubble" slows down.
Forgot to modell those Earthpieces flying, but i think you can imagine it. Just something to double the BigKaboom-Factor.
3d models for the explosions would be cool, though. Modern games use modeled explosions and manage to pull off amazing effects with very few particles. E.g. Company of Heroes.
"Very few" is a lot different than making a model. "Very few" is 20 particles, with animations and/or shaders to create really dynamic-looking FX from very few actors. What Picasso's talking about would... yikes... trust me, that Sphere thingy from SJ's code is bad enough, now that I've had it to test...