Mushroom clouds, how do they form?
The mushroom-shaped cloud that forms after the detonation of a nuclear blast has become a rather iconic image in recent times. But why does the cloud form this way?
The mushroom cloud effect all comes down to the Rayleigh–Taylor instability phenomenon. It starts with an explosion! Explosions allow for the sudden release of heat, which causes the air around the explosion to expand and become less dense. The hot air rises fast, creating a vacuum around that sucks more air towards the heat. As the air heats, it keeps expanding and rises. Ultimately a column of air forms by driving heated air upwards.
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If the column of air becomes high enough, it will reach altitudes where the atmosphere is the same density as the hot air in the column. At this point, the smoke will billow outwards in the “cap” of the mushroom. Because the air in the center of the column will remain much hotter than the air around the edges, the air in the center rises faster, creating an effect where it seems like the edges are curling downwards. The downward curling of the colder edge regions of the column appears similar to that of a mushroom. The bigger the explosion, the more likely it is that a mushroom-shaped cloud will form.