Surface mining

Surface mining and deep underground mining are the two basic methods of mining. The choice of mining method depends primarily on depth of burial and thickness of the coal seam. Seams relatively close to the surface, at depths less than approximately 180 feet (55 m), are usually surface mined. Coals that occur at depths of 180 to 300 feet (91 m) are usually deep mined but, in some cases, surface mining techniques can be used. For example, some western U.S. coals that occur at depths in excess of 200 feet (61 m) are mined by open pit methods, due to thickness of the seam (60-90 feet). Coals occurring below 300 feet (91 m) are usually deep mined.[4]
Modern surface mining