Mushroom Cloud

When large amounts of energy are released quickly close to Earth's surface, a dynamic pyrocumulus phenomenon known as a mushroom cloud results. Unsurprisingly, mushroom clouds are usually (but not always) shaped like mushrooms, and you can read more about them here:
Mushroom clouds

In the public consciousness mushroom clouds are usually associated with nuclear explosions, but in reality any old explosion will do so long as enough energy is released close enough to the ground. Large conventional explosions, volcanic eruptions, and asteroid impacts also produce mushroom clouds under the right conditions. The basic idea is that big explosions energize large volumes of air, causing the space around the energy pulse to expand, become fluffier than the air around it, and rise to an altitude where the water vapor contained in the mushroom stem condenses into cloud. At some point, the cloud expands further due to the reduced pressure at altitude, and eventually it drifts and disperses with the prevailing winds. There's a lot more going on in a real mushroom cloud than just that, though. The reader is encouraged to see what Wikipedia has to say.

Not all nuclear and exotic explosions create mushroom clouds. Nukes detonated underwater, underground, or above the atmosphere disperse their energy differently, as do asteroids that break up high in the atmosphere. The energy released by the Chelyabinsk meteor earlier this year was comparable to that of an ICBM-sized thermonuclear weapon, but it was delivered over a long enough time high enough in the atmosphere that it created a plasma train rather than a mushroom cloud. Likewise, shield volcanoes that deliver their heat slowly to the surface emit plumes of gas rather than mushroom clouds. Interestingly, nuclear mushroom clouds do have one distinctive feature that chemical, volcanic, and impact clouds lack. The initial fireball of a nuclear explosion is so hot it transforms some of the nitrogen and water vapor around it into nitrogen dioxide and nitric acid, tinging a nuclear cloud an industrial-gunk reddish-brown color. Volcanoes are just too cool to do this.

Sometimes I have a hard time selecting the images to go with these posts. I like that the one above is distinctive in its absence of a stem and jarring in the juxtaposition of the sublime beauty of a horrifically-exotic physics event with the gentle, feminine beauty of the dancer. Mushroom clouds are a sign that something wicked, and possibly truly evil, this way comes, but their forms are intricate and charmingly pretty. This picture early in the Wikipedia article must be one of the best displays of that beauty ever captured: