Asked by: Patrick Cook, by email
Underground fires are a surprisingly frequent phenomenon, the fuel being coal and the fire travelling along the seams. Such fires travel slowly because of the limited supply of oxygen, but can burn for a very long time: the underground fire at Burning Mountain Nature reserve in Australia is thought to have been going 5500 years. The number of such subterranean fires worldwide is incalculable. According to one study, subterranean fires in China alone are consuming some 200 million tonnes of coal a year and pumping as many pollutants into the atmosphere as all the cars in the US. As you can imagine, such fires are contributing substantially to global warming.
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