system
Given the following post, respond as if you're commenting on Reddit:
human
Which of a nuclear explosion's effects are unique to it being nuclear?

Radiation and fallout are obviously due to the radioactive fuel source, but what about things like the flash or mushroom cloud? How many of, say, Little Boy's effects could be replicated with 12,000 tons of conventional explosives?
gpt
Mushroom clouds are not unique to nuclear explosions, it’s just a result of fluid-dynamical instabilities (Rayleigh-Taylor, and subsequently Kelvin-Helmholtz). If you put a denser fluid above a less dense fluid (including fluids of the same composition, but with a downward temperature gradient) buoyancy drives any perturbation on the interface to grow. That’s Rayleigh-Taylor, which drives the stem of the mushroom cloud upward. Then if you have two fluids in contact moving with different velocities at the interface, that causes perturbations at their interface to grow. That’s Kelvin-Helmholtz, and it creates the swirl at the top of the stem, giving a mushroom shape. So this is just the behavior of air when you make it very hot, and a nuclear explosion is just one way to make a region of air very hot.

Like you said, ionizing radiation and residual radioactivity are due to the nuclear reactions that occur, or decays of radionuclides that were present in the nuclear weapon itself. So that’s unique to some kind of nuclear device.

But also the thermal effects, including thermal radiation (not all of which is ionizing). The temperatures reached by a nuclear detonation are many orders of magnitude higher than what would be reached with conventional HE.