Strip Mining: A Destructive Way of Coal
31-05-2017· Surface mining existed as well, but it wasn't until the big shovels came on in the 1940s and 1950s that strip mining began to take a larger portion of the state's annual coal production. Generally it is economic to strip mine when there is a 20:1 ratio of overburden-to-coal seam, meaning, for example that a three-foot coal seam can be surface mined economically when the overburden is up to