Quarry blast

you're going to have to do a lot of figuring out and tests, just like the 
rest of us.

there's a nice reactor demo in the scene folder, something to do with teapot 
and rockets.

reactor does some debris falling, but you can also do simple debris with 
particles and/or pflow.   to do simple bouncing rocks, just make a low poly 
collision version of the volcano (non renderable) that particles bounce and 
skid down. 

smoke, can use tons of small greyed spherical particles or chinz it with 
facing plane smoke planes, as in the teapot/rocket example above. 

you'll probably use a half dozen different things to make it look decent. 
good luck.