The ground underneath the small former mining town of Centralia, in Pennsylvania, has been on fire since 1962, when a coal seam running into a mine shaft set on fire. It hasn't stopped ever since.

While no one is sure how underground coal began burning, The Washington Post interviewed expertswho say it will probably keep burning for another 250 years.

According to engineers, the only way to stop the fire is to dig the entire 3,000 acres (1215 ha) of coal field under the ghost town and surrounding area, which would cost about $600 million.

Image courtesy of the U.S. Office of Surface Mining Reclamation and Enforcement.

Centralia was once a prosperous coal mining town with a population estimated in 1,100 people. It had four movie theatres, seven bars, a school and a gas station.

Today, even the US postal service has scratched the town’s zip code from its system, and it is no longer printed on most modern maps.

Here’s the American Chemical Society's Reactions latest video explaining why coal mines have a tendency to burn: