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## Coal Mining

Coal is extracted from Earth using one of two major methods:

Sub-surface (strip) mining.

Sub-surfacing mining is used when seams of coal are located at significant depth below Earth's surface. The first step in sub-surface mining is to dig vertical tunnels into the earth until the coal seam is reached. Horizontal tunnels are then constructed off the vertical tunnels. In many cases, the preferred way of mining coal by this method is called room-and-pillar mining. In room and pillar mining, vertical columns of coal (the pillars) are left in place as the coal around them is removed. The pillars hold up the ceiling of the seam, preventing it from collapsing on the miners working around them. After the mine has been abandoned, however those pillars may collapse, bringing down the ceiling of the seam and causing the collapse of land above the old mine.

Surface Mining.

Surface mining can be used when a coal seam is close enough to Earth's surface o allow the overburden to be removed easily and inexpensively. In such cases, the first step is to strip off all of the overburden in order to reach the coal itself. The coal is then scraped out by huge power shovels, some capable of removing upto 100 cubic meters at a time. Strip mining is a far safer form of coal mining for coal workers, but it presents a number of environmental problems. In most instances, an area that has been strip-mined is terribly scarred. Restoring the area to its original state can be a long and expensive procedure. In addition, any water that comes in contact with exposed coal or overburden may become polluted and require treatment.