Underground coal fires are quite common throughout the world, often in coal mines. Coal seams can be ignited by lightning or wildfires and the seam can continue to burn indefinitely, even after the surface fire has been extinguished. The fires are extremely difficult to extinguish and often are the source of new bush fires.
The oldest known coal seam fire in the world has been smouldering for some 5,500 years at Burning Mountain, north of Scone in NSW. Early explorers assumed Burning Mountain’s billowing smoke and peak of grey, smouldering ash was an active volcano but it was, in fact, a coal seam fire.