Ed Huntress wrote:

(...)

Did you see the town of Centralia? I used to play Little League ball against
their team, when I lived in Bloomsburg. Nice town. Now is has, I think, 5
residents. The seam under it has been burning since 1962. Heating a house
there must be cheap.

http://en.wikipedia.org/wiki/Coal_seam_fire

It seems unlikely that all the oxygen necessary to support that
level of combustion comes from 'ventilation' to atmosphere.

If so, I'd expect the intensity of the fire to 'bank and flare' at
some frequency as the level of oxygen changes with time, predicated
on the pneumatic resonant frequency of the cavity.

I wonder if the most persistent seam fires are enabled by chemical
oxidisers already in place?

--Winston