An underground fire that began in 1962 in the town of Centralia, Pennsylvania, is still going some 53 years later.
The coal-mining town in the north eastern state sits on top of some of the largest coal deposits in the world, as explained in the YouTube video by the American Chemical Society called Reactions.
Just over half a century ago the coal tunnels, which had been in use since the 1800s, were set ablaze. It is unclear how the fire started, but the most popular theory is that the burning of rubbish nearby somehow made its way down the tunnel and ignited the slow-burning coal.
The video claims that the residents of Centralia found the situation "amusing" at first because it did not pose a threat to them. However, eventually the burning started emitting sulphurous fumes that made their way to the town, putting the locals in danger.
Additionally, the underground heat weakened the roads, making it vulnerable to sink holes.
There have been several attempts to quash the blaze that have ultimately proved unsuccessful, and experts fear that it could burn for another 250 years.