The Centralia mine fire is a coal seam fire that has been burning underground since 1962. It is believed the fire was started at a dump on May 27th as the city was trying to clear the dump. The visible flames were put out, but on May 29th, flames were seen again. This repeated itself again on June 4th and a bulldozer was brought in to stir up the garbage so the firemen could get to the concealed layers. Days later a 15 foot wide hole was found where garbage had once concealed the hole. It is possible the hole led to a pathway to the old coal mines beneath.
Roads - Misc, Fires
The fire continues to burn over 50 years later and at its current pace it may continue for another 250 years.
Links: en.wikipedia.org, www.csmonitor.com