Yeah, weird for sure. It's amazing what imagery and scenes the mind can produce.

Anyway, I'm not sure about the inverted volcano but according to my favourite dream meanings site, both mice and insects represent minor issues which you're sort of dwelling on or maybe processing. I have a feeling the inverted volcano is your mind, and the mice and insects, the minor issues, are being ejected, perhaps solved or dealt with.

If it was my dream I'd probably look at it that way.