These are photographs of avalanches. A snow avalanche is also a dense cloud of particles. It is ground hugging and exhibits the cauliflower look of dense fluids in motion.
So when you state:
You are in fact not using even common terms such as a debris avalanche, but instead use a loaded word improperly.

So when you state:
In attempting to describe a phenomena that has never occurred before, we attempt to use terms that are close to it; pyroclastic flows are what most closely resembles what happened on 9/11.
You are in fact not using even common terms such as a debris avalanche, but instead use a loaded word improperly.