Just fyi, I moved this thread to the correct forum as it is dynamics and effects related
Second, regarding your dust and debris, your best bet would be to either do it in post, as it is just coming directly at the camera, depending on the compositor you are using.
Or, simply emit particles from your falling rocks, and maybe an instancer for smaller debris
Good luck!
Israel "Izzy" Long
Motion and Title Design for Broadcast-Film-DS
izzylong.com