[Intro]
The signs as you approach the eastern Pennsylvania town of Centralia ominously warn of danger and death.
Ignore those signs and you're soon surrounded by a post-apocalyptic scene.
The houses are razed, the fields empty and the roads mangled by overgrowth and vegetation.
And then, there is the toxic smoke billowing from
beneath the mostly abandoned town through fissures and holes in the earth.
The ground below is literally on fire,
and it has been for more than fifty years.
A seam of coal thirteen kilometers long
and encompassing more than fifteen square kilometers
is burning under the old mining town.
This blaze started in 1962 most likely when sanitation workers began burning trash at a landfill
too close to the entrance of an abandoned mine.
Today, it remains the most infamous coal fire in the United States.
But the phenomenon is hardly unique:
More than 150 coal fires are burning right now in the U.S.
while thousands more range in at least twenty other countries around the world.
In China alone, underground coal fires
are thought to burn more than 200 million metric tons of coal each year:
roughly ten percent of the nation's total annual production.
And it's not just careless humans who are to blame.
Coal fires can, and often do, start spontaneously.
And by "spontaneously" here, I don't mean, like,
"suddenly", or "quickly".
When we're talking about thermodynamics, a reaction is spontaneous
when it occurs without the input of energy from an outside source to drive it along.
It just goes.
Low-grade, soft coal is more likely than other types
to spontaneously combust, sometimes at temperatures
as low as 40 degrees Celsius,
especially when it's near the surface and comes into contact with open air.
It begins when the coal reacts with oxygen in the air
or oxidizes, the same way that iron exposed to air oxidizes and rusts.
When things oxidize, they give off heat.
Burning is just rapid oxidation giving off lots of heat.
Eventually, the temperature of the coal gets high enough
for long enough that it evaporates any remaining moisture in it.
That's when ignition can occur, and when bad things start to happen.
Coal fires can be caused non-spontaneously, like by a lightening strike
or a brush fire, in addition to human activity,
but either way, once it's ignited,
the fire takes advantage of the all-you-can-eat coal and oxygen buffet.
Many coal fires smolder for years unnoticed below the ground, but eventually the coal starts turning into ash.
This creates voids in the earth that cause the ground above to collapse,
creating sinkholes that can destroy roads and buildings.
And these collapses just give the fire access to more oxygen,
extending the life of the blaze.
Coal seam fires move relatively slowly,
maybe two meters per month.
But they can easily spread to other nearby deposits.
The fires also, of course, release a toxic brew of emissions
including Benzene, Sulfide, Mercury, and Arsenic,
not to mention Methane, and CO2.
Coal fires are especially troublesome when they ignite in underground mines
where the oxygen in plentiful thanks to ventilation systems,
and the blaze becomes nearly impossible to extinguish.
This is the case in Centralia, where the fire continues to burn at depths of up to 100 meters.
Officials tried for nearly two decades to put out the Centralia fire using methods that included
digging trenches, and pouring down wet sand, gravel and cement in an attempt to cut off the oxygen supply.
But the cement in particular tended to have the opposite effect thanks to temperatures in excess of 537 degrees
that burned away all of the fill material leaving more gaps for oxygen.
Nothing worked!
Even fighting the toxic flames at the surface proved fruitless,
and eventually the US government allocated 42 million dollars to relocate residents and businesses.
What was once a town of more than two thousand,
now has a population of a dozen or so holdouts who refuse to leave.
The residents who left won't be returning.
Scientists estimate that there is enough coal beneath Centralia to fuel the fire for another 250 years.
And yet that's nothin' compared to Australia's aptly named Burning Mountain,
under which a 𝟔,𝟎𝟎𝟎 𝐲𝐞𝐚𝐫 𝐨𝐥𝐝 𝐟𝐢𝐫𝐞
continues to burn through a seam of coal in the Earth.
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[Outro]