system
Given the following post, respond as if you're commenting on Reddit:
human
ELI5: If an atom splitting causes a nuclear explosion, could a natural coincidence cause one?

I suppose this question boils down into two factors:
A) Are nuclear explosions something only mankind can do (a specific reaction that may never happen naturally)?
B) If not, does that mean an atom could suddenly be split by some freak coincidence and create a nuclear explosion, possibly in a populated area?

Thanks in advance!
gpt
Instable atoms split all the time in nature.

What causes a nuclear explosion is a chainreaction where one splitting causes multiple more. 

This is only possible if you have enough instable material gathered in one place (critical mass) wich will instantly explode. Thats how they are triggered. Take something below critical mass and smack a little more Uranium on it. 

It's a statistical property but the chance of Uranium below the critical mass getting a chainreaction going is just too low to think about it. Imagine you roll a dice and whenever you have a 6 you roll 2 more times. How high is the chance to get a billion throws before each chain ends?

Atoms lighter than iron (so most we see in our daily life) do not release energy when they split. Other heavy atoms do not split spontanously because they are stable. It's really just a few radioactive materials that work for this process because they are large and instable.