Sean Ryan wrote:A question came up at my last grotto meeting that no one had an answer to. Every once in a while coal catches fire underground. There's been one burning under Centralia, PA, for the past couple decades. The recent movie Silent Hill involved a similar underground coal fire (only vapors from the coal wafted up and killed half the town).
Once a coal fire burns out, will there be a cave? Any passages people would be able to explore?
Interesting thought - is this an overlooked avenue for non-limestone speleogenesis? Consider the scenario of a deep coal seam under some relatively stable overburden. Seam catches fire somehow (mine accident, lightning strike, lava intrusion, whatever) and burns for a long time. Eventually, the fires go out and what had been a coal seam is now filled with ash, clays, etc. Add water to flush out the residuals and, viola, cave!