A Mushroom cloud rising white, blotting horizon, in OP Ivy, Mike shot atomic bomb test blast. (Photo by Time Life Pictures/Us Air Force/Time Life Pictures/Getty Images). Copyright: Time & Life Pictures

A mushroom cloud is a distinctive pyrocumulus mushroom -shaped cloud of condensed water vapour or debris resulting from a very large explosion . They are most commonly associated with nuclear explosions , but any sufficiently large blast will produce the same sort of effect. They can be caused by powerful conventional weapons like the GBU-43/B Massive Ordnance Air Blast bomb . Volcanic eruptions and impact events can produce natural mushroom clouds.
Mushroom clouds form as a result of the sudden formation of a large mass of hot, low-density gases near the ground creating a Rayleigh–Taylor instability . The mass of gas rises rapidly, resulting in turbulent vortices curling downward around its edges, forming a vortex ring and drawing up a column of additional smoke and debris in the centre to form its "stem". The mass of gas eventually reaches an altitude where it is no longer of lower density than the surrounding air and disperses, the debris drawn upward from the ground scattering and drifting back down (see fallout ).

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