Underground fires

Underground fires
Main article: Coal seam fire
Most underground fires are caused by the mineral marcasite.[citation needed] chemical formula FeS2, it is chemically, the same as pyrite (fool's gold) but structurally complex. Marcasite and pyrite very commonly occur in association with coal beds. these minerals form the source of the sulphur which occurs within the coal. Marcasite is highly unstable at pressures and temperatures close to the earths surface. due to its unstable nature, it may react spontaneously, consuming itself and releasing heat. In the event that sufficient heat is generated and coal occurs close by, the coal may be set alight underground and such a blaze may go on burning for tens to hundreds of years.
There are hundreds of coal fires burning around the world.[41] Those burning underground can be difficult to locate and many cannot be extinguished. Fires can cause the ground above to subside, their combustion gases are dangerous to life, and breaking out to the surface can initiate surface wildfires. Coal seams can be set on fire by spontaneous combustion or contact with a mine fire or surface fire. A grass fire in a coal area can set dozens of coal seams on fire.[42][43] Coal fires in China burn 109 million tons of coal a year, emitting 360 million metric tons of CO2. This contradicts the ratio of 1:1.83 given earlier, but it amounts to 2-3% of the annual worldwide production of CO2 from fossil fuels, or as much as emitted from all of the cars and light trucks in the United States.[44][45] In Centralia, Pennsylvania (a borough located in the Coal Region of the United States) an exposed vein of coal ignited in 1962 due to a trash fire in the borough landfill, located in an abandoned anthracite strip mine pit. Attempts to extinguish the fire were unsuccessful, and it continues to burn underground to this day. The Australian Burning Mountain was originally believed to be a volcano, but the smoke and ash comes from a coal fire which may have been burning for over 5,500 years.[46]
At Kuh i Malik in Yagnob Valley, Tajikistan, coal deposits have been burning for thousands of years, creating vast underground labyrinths full of unique minerals, some of them very beautiful. Local people once used this method to mine ammoniac. This place has been well-known since the time of Herodotus, but European geographers misinterpreted the Ancient Greek descriptions as the evidence of active volcanism in Turkestan (up to the 19th century, when the Russian army invaded the area).
The reddish siltstone rock that caps many ridges and buttes in the Powder River Basin (Wyoming), and in western North Dakota is called porcelanite, which also may resemble the coal burning waste "clinker" or volcanic "scoria".[47] Clinker is rock that has been fused by the natural burning of coal. In the Powder River Basin approximately 27 to 54 billion tons of coal burned within the past three million years.[48] Wild coal fires in the area were reported by the Lewis and Clark Expedition as well as explorers and settlers in the area.[49]