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This drawing depicts area surface mining. Surface mining is accomplished by removing overburden from the coal seam and then blasting and removing the coal. The ratio of overburden excavated to the amount of coal removed is called the overburden ratio. The lower the ratio, the more productive the mine. The lowest overburden ratios are found in western surface mines. In Appalachia, often more than one coal seam is mined.
There are several types of surface coal mines. Area surface mines, usually found in flat terrain, consist of a series of cuts 100 to 200 feet wide. The overburden from one cut is used to fill in the mined out area of the preceding cut. Contour mining, occurring in mountainous terrain, follows a coal seam along the side of the hill. When contour mining becomes too expensive, additional coal can often be produced from the mine's highwall by the use of augers or highwall miners. Open pit mining is usually found where coal seams are thick. Open pit mines can reach depths of several hundred feet.
Equipment used in surface mines include draglines, shovels, bulldozers, front-end loaders, bucket wheel excavators and trucks. In large mines, draglines remove the overburden while shovels are used to load the coal. In smaller mines, bulldozers and front-end loaders are often used to remove overburden.
Click here to see surface miners at work.
