Deep beneath the rugged terrain of northern China, flames are gnawing their way through the country's extensive coalfields. While the world focuses its attention on more visible crises, China's underground fires are quietly consuming up to 200 million tons of coal each year. The fires spew nearly as much carbon dioxide into the atmosphere as do all the cars in the United States.
John van Genderen, a geomorphologist at the International Institute for Aerospace Survey and Earth Sciences in the Netherlands, is leading an international high-tech counterattack. Heat measurements from satellites, airplanes, and ground-based detectors have been combined to determine the size and depth of the fires and which direction they are burning.
Some fires started naturally by lightning or spontaneous combustion, others as a result of coal mining. Either way, extinguishing the smoldering coal is a laborious process. Chinese workers suffocate surface fires by burying them under a 3-foot layer of dirt. Deeper fires, some of which have persisted for centuries, are more difficult. Quenching them with water can produce explosive methane fumes, so engineers pour a water-clay slurry into cracks created by the heat of the flames. Even after treatment, the ground can take several years to cool down.
"These coal fires weren't given due attention in the past," says Anupma Prakash, a thermal remote-sensing expert who works with van Genderen at the institute. Along with Chinese partners, Prakash has helped alert the Chinese government to the magnitude of the problem, but he recognizes that nature has the upper hand. "Putting out all the fires in one go is not possible. Sometimes it is more feasible to isolate the fire and let it burn," he says.