United States had burned 1.1 billion short tons of coal in 2007, that is enough to fill a railroad car every 3 seconds. Almost over 90% coal was burnt by electricity sector and rest was burned mostly in industrial and commercial settings. Burning vast quantity of coal by power plants relies on a vast network of mines where companies excel at extracting it from the Earth at prolific rates.
There is a simple principle for removing coal that just expose it, break it up, and cart it off to be burned. In fact practically coal mining is energy intensive, labor intensive and money intensive undertaking. One of the most risky occupations is the underground mining, killing and injuring many in accidents, and causing chronic health problems. Most of underground mining is done in the East and surface mining is done in the West.
Because of different influences the coal mining industry had got dramatic changed over the past few decades. Surface mining methods had overtaken underground mining for extracting coal though surface mining is more productive but damaging environment more. Worst than all is mountaintop removal in which top of the mountain is blasted away to get to the coal seam underneath. The amount of coal produced per worker had risen also dramatically, resulting in overall employment in mining being roughly cut in half between the 1980s and the 2000s.
Though the portion of coal still mined underground with help of heavy power and efficient machinery, while with less manpower. On whole coal mining today in United States is so much different as it was few decades before.
Underground Mining
There are two major methods for underground mining one is room and pillar, and other is longwall mining.
In room and pillar mining, seams of coal are not mined completely; large pillars of coal are left to support the overlaying layers of rock. By this way mining creates a network of alternating open spaces and large pillars of coal. After completing mining in one part of the coal seam, then miners do “retreat” mining so that coal can be extracted as much as its possible in the remaining pillars on the way out, while doing that the roof of the seam begins to collapse behind them.
In longwall mining long tunnels are dug in to coal seam and removing the extracted coal by conveyor belt. When the miners and machinery moves along the seam, then to support the ceiling of overlaying rock on the place a hydraulic support system temporarily holds it.
Today both room and pillar and longwall mining are done with heavy and powerful mining machines that rapidly cut coal from the face of coal seams. These machines are phasing out the use of less productive and more dangerous traditional methods like intermittently drilling the coal seam and blasting it with explosives.
Surface Mining
Surface mining is done only when the coal seam is located much closer to the surface. This method requires many fewer workers per unit of coal produced and uses very large machinery. Before extracting the coal from surface first vegetation and soil is cleaned out from surface. Then the large intermediate layer of the sediment and rock is blasted off. When the underlying coal is exposed then it is extracted in strips and moved by conveyor belt or truck to its final destination. There is law when surface mining will be completed then coal bed will be restored and re planted with vegetation. Though to date the acres of surface mines that have been successfully reclaimed is relatively low compared with acres of newly mined land.
Mountaintop Removal Mining
Though coal mining had caused environmental damage but the most destructive mining method so far is a relatively new type of a surface mining called mountaintop removal (MTR). Currently this method is being used in southern West Virginia and eastern Kentucky, according to this all trees are stripped off from the mountain top and then the top is blasted away several hundred feet with explosives. The scattered wreckage is dumped into an adjacent valley, which bury the streams and destroys everything that once grew there. After the blast it lefts behind a flattened area with soils so poor they can only support exotic grasses, a profound change from a once diverse and heavily forested ecosystem. The main damage from MTR is great loss and fragmentation of ecosystems, higher risk of local flooding and runoff, contamination of local ground water resources and occasional deadly accidents.
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