Nice and moody. I like the flying debris (procedural rocks?), although I think you could throw some more in. And is that a tree I see on the left? I think it would have burst into flames at this point. Perhaps just a little more (reflected) light on the volcano itself would enhance it, so you'll see some ground structures. If you could get the clouds to be more violent, bulbous, and perhaps multicolored it would be great, but in my attempts I didn't quite make the 'exploding clouds'.
---Dune