Phenomena[]
A mushroom cloud is a distinctive post-bast pyrocumulus mushroom-shaped cloud of debris, hot air, gaseous vapour (usually condensed water vapour and usual air components like nitrogen gas) and smoke and resulting from the occurrence of a large explosion. The buoyant mass of gases, vapour and entrapped debris rises rapidly, resulting in turbulent vortices curling downward around its edges, forming a temporary vortex ring that draws up a central column, possibly with smoke, debris, or/and condensed water vapour to form the "mushroom stem". When it cools and reaches a certain hight it will mostly fall back to earth as fall-out.
They are most commonly associated with nuclear explosions and atomic weapons going off on or near the ground, but any sufficiently energetic detonation or deflagration will produce the same sort of effect such as the conventional ATBIP, exploding arms depots, exploding arms ships, rocket fuel factories, massive gas works explosion and so on...