I can't find any posts about this, but I have a hard time imagining that it has not come up.
Not far from the Rally site is Centralia, PA, the town that had it's underground coal catch fire. It has since been mostly evacuated but continues to smolder underground. It's worth a 30 minute stop to look around.
Google it or use wikipedia for more information.
Here you see the old road that is cracked and buckled from the heat, with smoke coming out. It's sort of like Yellowstone in the East!