bellarmine.lmu.edu/faculty/fjust/Images/mushroom-cloud.gif
Why do nuclear explosions form a mushroom cloud?
Mushroom clouds generally are formed when a massive fireball is created by an explosion. Due to the fact that the fireball is less dense than air it quickly rises forming the top of the mushroom cloud. The fireball leaves a stalk of heated air behind it and this air acts as a chimney by sucking in any smoke and hot gases from ground fires. Since the center of the cloud is the hottest part of the cloud it rises quicker than the outsides of the mushroom cloud. This gives the impression that the top of the cloud is curling down giving the cloud a fungal form. Mushroom clouds are simply formed by convection and can be created by many types of explosions, not just atomic bombs.
www.chemistry.Pomona.edu/Chemistry/periodic_table/Elements/Cobalt/mushroom%20cloud.jpg
