# How long would it take for a large impact crater to stop being volcanic?

(For context, this is for a science fiction novel in which a chunk of an earth-like planet is expelled. I suppose the nearest real-world situation would be a large meteorite strike.)

Suppose an impact, explosion, or other "large" event strips away the lithosphere over a reasonably large chunk of the Earth's surface. For about how long would the area remain highly volcanic?

To explore this, I wrote a crude numerical simulation of radiation into space (using the Stefan-Boltzmann law, assuming no atmospheric blanket) and conduction in the mantle (using Newton's Law of Cooling, assuming no convection).

If you're curious, the code is here. It produces somewhat sane results.

This shows temperature (Kelvin) at various depths (metres) over a few decades. The surface cools to boiling after a few years, and we have 20 metres of solid rock after about 20 years.

That much seems intuitively reasonable, but it doesn't answer my question. Perhaps this model in combination with some other information would get me there.

For example, if we could say "we need about 100m of solidified surface rock at <1000K to prevent volcanic activity generally, but we would still expect specific points of intense volcanic activity for at least a hundred years after that", that would answer the question for my purposes.

What geological conditions would need to occur after such a cataclysm for the surface to stabilise? Say, to the point that a human with breathing apparatus could walk around on it, or that it would look fairly boring from space?

• Not sure which phenomenon you are referring to. If you think stripping away the lithosphere would expose some king of molten interior, it's wrong, the mantle is solid. If you think impact melting, it generally form a melt layer under a breccia layer. These sheets can take tens to a few hundreds kyr to cool down, see doi.org/10.1016/j.epsl.2021.117013 and references therein. I'm not sure if these melt layers are associated with volcanism, they just slowly crystallize. Mar 11 at 8:42
• There is also the (highly debated) hypothesis that large impacts can trigger volcanism on the other side of the planet because of the antipodal focusing of seismic waves. Its been proposed for several impacts here on Earth, and also on Mars, see for instance this answer: earthscience.stackexchange.com/a/23665/18081 Mar 11 at 8:47