@SpectateSwamp said:
We need a mushroom expert to join the thread. I don't want the Latin name either.
Uh... haven't you noticed that I am the "expert" here for all things weather? I have a few of these things called degrees which certify that I know meteorology. I have even published a paper and given some small presentations at professional conferences. I am telling you that those are not mushroom clouds. They are anvil clouds. The reason they flatten out at the top is that the rising air that forms the cloud cannot rise anymore, but has to move out of the way of rising air below. Thats what forms the spreading that you see in anvils.
Mushroom clouds from nuclear and volcanic explosions have the "rolling" effect due to the fact that air further from the center do not get as much upward force, thus they move slightly slower. Eventually, this air cannot rise as much either and will eventually "hit a ceiling" and flatten out.
I know SpectateSwamp will completely disregard all of this and I am not sure why I just spent the last few minutes writing this. Maybe somebody will remember this useful bit of trivia?