The mushroom cloud produced by a hydrogen bomb explosion

The formation of a mushroom cloud is caused by the release of an immense amount of energy. When a nuclear device detonates, a large amount of high-energy particles such as X-rays, neutrons, and α particles are produced over a wide surrounding area. These particles not only have the power to destroy all structures and kill all living things within a large range, but they also rapidly heat up the surrounding air. This superheated air, mixed with a large amount of dust, rises quickly due to the force of the explosion and buoyancy.

At first, the rising air forms a vertical column of clouds. As this column ascends and expands, its top layer of air and dust encounters cooler air above and begins to cool down. When the rising air and dust cool to nearly the same temperature as the surrounding air, their ascent slows. They then change direction, moving horizontally outward around the surroundings, and eventually begin to descend. Because the changes in the "cloud column" at its top generally occur uniformly in all directions, the characteristic shape of a mushroom cloud is formed.