I have been thinking about this lately. There are huge underground coal fires in China, one supposedly 3000 miles long. This article is about one in Pennsylvania.
In 1962, a small community in rural Pennsylvania prepared for a Memorial Day celebration. On the town’s edge, near the Odd Fellows Cemetery, sat an old mining pit turned municipal landfill. To control its smell and vermin, the story goes, volunteer firefighters set a small fire in the trash, let it burn for a few hours, and, after dousing the flames with water, left a smoking pit. Today, on what was once Route 61 just outside town, appears a spray-painted greeting: “Welcome to Graffiti Highway.” About twenty feet down the road, smoke rises, almost imperceptibly, from a buckle in the paved sea of heart-encircled initials and crossed-out phone numbers. Some believe that Memorial Day trash fire ignited a seam of coal, the Buck Mountain vein, and started an underground inferno that still burns. If no one stops it—and no one plans to—some geologists estimate that it could continue burning for another two centuries.
There is a discussion about the ways that the fires are controlled and sometimes stopped.