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Fire in the Hole

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Author Topic: Fire in the Hole  (Read 153 times)
Lisa Wolfe
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« on: June 18, 2009, 11:59:30 pm »

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. Those conflagrations formed “clinker”—a hard mass of fused stony matter. Surfaces formed in this way resist erosion far better than adjacent unfired ones, leaving clinker outcrops. Many ancient fires like those still burn, from the Canadian Arctic to southeast Australia. Scientists estimate that Australia’s BurningMountain, the oldest known coal fire, has burned for 6,000 years. In the 19th century, explorers mistook the smoking summit for a volcano.

Natural though the fires may be, humans intensify the scale. China, for example, supplies 75 percent of its energy with coal as it hurtles toward industrialization. Due to mining of its vast coal fields, fires are spreading. Estimates vary, but some scientists believe that anywhere from 20 million to 200 million tons burn there each year, producing as much carbon dioxide as about 1 percent of the total carbon dioxide from fossil fuels burned on earth. Another human intensifier: rural Chinese people tend to hand-dig household coal from hundreds of thousands of surface locations, then abandon them when the cavities get too deep. The practice leaves the earth punctured by countless small pits; inside, loose coal chunks and powder are exposed to air, making them highly combustible.
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