From Envirowiki

Strip Mining (also known as open cut mining) is the process of cutting deep trenches to remove minerals such as coal and phosphate found near the earth's surface in flat or rolling terrain. It is a type of surface mining. This type of mining is generally only feasible when there are large amounts of mineral to be extracted very near the surface. The two forms of strip mining are area strip mining, used on a flat terrain, and contour strip mining, which is used on more hilly terrain. Area strip mining is used to extract deposits over a sizable parcel of land. Contour strip mining uses terraced strips along the contours of hills and mountains to remove the minerals (not to be confused with mountaintop removal mining).