Why do nuclear bombs explode into mushroom clouds?

Spark Global Limited reports:

Spark Global Limited reports:

Why do nuclear bombs explode into mushroom clouds? What causes this iconic shape? When a nuclear bomb explodes, energy is released indiscriminately in all directions, so why does it produce a mushroom cloud instead of an expanding fireball?

Although the energy burst does initially form a “ball of hot air,” it’s only the beginning, says Katie Lundqvist, a computational engineering researcher at Rensley Fermor National Laboratory in California. As the hot air gradually rises, the cylindrical sphere in the middle will sustain more buoyancy than the edge regions.

 

This is how the shape of the sphere is formed. When the largest low-density fluid is in the middle, it rises rapidly, much like a cupcake in an oven that is gradually expanded by heat. Although the entire sphere of fluid is rising, the middle cylinder is rising more tightly, and cold air from outside the sphere starts to rush under the rising bubble.