Catlin, I have a tutorial on creating tornado in Bryce. By Alex Aurichio, if it's any help. It's just one jpg of 152 kb. He used "626 2D faces, several tree meshes and a truck, all randomly dispersed and rotated using the edit controls" to create the debris that whirls in the tornado. Maybe you could try with 2d pics of rocks and/or stones, dispersed and scattered trough the controls. Or you might try with Scatter. bantam3d.com. As to the suggestions, I agree with lsstrout. Drop the lava texture on the protrusions and leave it just on the pools below.

-- erlik