Centralia, Pennsylvania: The Ghost Town Atop an Inferno

Naturally occurring coal deposits are called "seams" in the mining industry. Wherever such veins occur, coal-seam fires (like the one under Centralia) are apt to break out.

"They are quite common," Anupma Prakash — a geologist at the University of Alaska, Fairbanks — tells us in an email.

China's 3,106-mile (5,000-kilometer) coal mining belt is notorious for its seam fires. So is the town of Jharia, India, where unwanted fires have claimed about 41 million tons (or roughly 37 million metric tons) of coal since 1918.

"The issue is more prevalent in areas where coal was extracted in the past with limited efforts to ensure that the 'hole' left from the extraction ... was filled up," says Prakash. Coal companies that don't provide "structural support" to keep the ground from collapsing likewise risk a mine fire.

Granted, humans aren't always responsible. Down in New South Wales, Australia, there's a famous coal seam under Mount Wingen that's been burning for 6,000 years straight. Scientists think it was first ignited by an ancient brush fire or lightning strike.

Anthracite coal doesn't need much encouragement to catch fire. Under the right circumstances, the material can actually light itself ablaze through spontaneous combustion.

"The decomposition of pyrite present in coal produces heat, and in some cases, this self-heating can start the coal on fire. This is a problem even where coal is transported long distances in ships," says research geologist Allan Kolker in another email exchange.

By most accounts, Centralia's great fire began at a dump near the local Odd Fellows Cemetery. On Sunday, May 27, 1962, this local landfill was intentionally set ablaze by the fire department, with six volunteer firefighters standing by. It was all part of a yearly cleanup effort the local city council organized.

Controlled burns were a popular garbage-disposal technique back then — but things didn't always go according to plan. By that time, coal production had slowed significantly, and there was a vast network of abandoned mines beneath Centralia's buildings.

Perhaps this fire ran deeper into the trash than anybody realized. If so, it could've spread through the refuse and entered the nearest coal mine pit, with no one being the wiser.

Then again, maybe the town government had nothing to do with it. Some have argued that a different garbage fire at the same site — lit by an unidentified truck driver — is what really sealed Centralia's fate.

Another (less popular) theory claims the coal-seam fire started all the way back in the Great Depression and went unextinguished for decades before the 1960s gave it a new lease on life.

Regardless, the inferno made itself right at home. Sweeping through mine tunnels and coal seams, flames descended as far as 300 feet (91.4 meters) below the ground, sometimes nearing temperatures of 1,350 degrees Fahrenheit (732 degrees Celsius).

The mine fire wasn't discovered until a resident found hot steam billowing out of a sinkhole in the backyard. The smoke was found to contain unsafe carbon monoxide levels, raising safety concerns among Centralia's residents.

According to a 2012 investigation, passageways underlying 400 acres (161.8 hectares) of land had been touched by the blaze at some time or other.

"Uncontrolled coal fires have all of the potential environmental impacts of burning coal for power generation, with none of the benefits," Kolker explains. "In addition to emitting carbon dioxide, trace metals such as mercury, and harmful fine particles are emitted."

"The fires also give out smoke and ... nasty gases," notes Prakash. Alongside the carbon dioxide, she tells us methane and "pungent-smelling" sulphur dioxide may also spew forth. "I can virtually smell that gas even when I talk about underground fires!" she says.

To this day, there is smoke rising from earth through fissures around Centralia. Meanwhile, the terrain has become perilously unstable ground over time.

"These [fires] are dangerous ... as land can suddenly collapse (sink) as the fire just 'eats up' the ground underneath," Prakash tells us. "Such collapses can damage houses, roads, train tracks, etc."

That's why Pennsylvania closed off 4,000 feet (1,219 meters) of the main highway Route 61 in 1993. Subterranean pillars that held up the pavement were destroyed or weakened by the flames, making the roadway totally unsuitable for motorists.

Extinguishing efforts didn't pay off. Between 1962 and 1982, assorted government agencies spent $7 million fighting the Centralia mine fire. Openings were sealed, trenches were dug and the mines were stuffed with noncombustible ashes, sands and crushed rock. Nothing worked.

Nearly all of Centralia's former residents are long gone; many residents accepted a $42 million taxpayer-funded relocation initiative which saw 500 buildings destroyed. The remaining Centralia residents have been granted permission to spend the rest of their lives in the town, as per a 2013 settlement with the Commonwealth of Pennsylvania.

According to the state's Department of Environmental Protection, the underground fire might keep on raging for over 100 years yet to come.

As bad as they can get, coal-seam fires aren't invincible.

"Good policies on mining safety and reclamation go a long way as a preventative measure. If a fire does start, taking ... quick action to contain it by isolating the fire, dowsing the fire, cooling the area, and continued monitoring to ensure that [the] fire does not start again are important measures," says Prakash.