Across the globe, thousands of coal fires are burning. Nearly impossible to reach and extinguish once they get started, the underground blazes threaten towns and roads, poison the air and soil and, some say, worsen global warming. The menace is growing: mines open coal beds to oxygen; human-induced fires or spontaneous combustion provides the spark. The United States, with the world’s largest coal reserves, harbors hundreds of blazes from Alaska to Alabama. Pennsylvania, the worst-afflicted state, has at least 38—an insignificant number compared with China (see sidebar, “Flaming Dragon,” p. 58) and India, where poverty, old unregulated mining practices and runaway development have created waves of Centralias. “It’s a worldwide catastrophe,” says geologist Anupma Prakash of the University of Alaska at Fairbanks.
Some of the underground fires are natural occurrences. When coal, exposed at or near the surface by erosion, combines with oxygen, a chemical reaction produces heat. That process can build for years; low-grade, soft coals—crumbly and low in carbon—can spontaneously combust, at temperatures as low as 104 degrees Fahrenheit. Lightning or a brush fire can also ignite soft coal. The fires burn downward, acquiring air through fissures in rock and microscopic spaces between grains of dirt. An underground fire may smolder for years, or even decades, without showing signs on the surface. Eventually, however, in a process called subsidence, burning subterranean coal turns to ash, creating huge underground voids and causing overlying ground to crack and collapse—thus allowing more air in, which fans more fire. Much of the landscape of the American West— its mesas and escarpments—is the result of vast, ancient coal fires.
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