Mountain Top Mining includes contour mining, cross-ridge mining, all forms of steep slope strip mining, and area mining, but does not include underground or deep mining. These devastating mining practices destroy the natural rock formation (geology) needed to stabilize the mountain. The water flow (hydrology), and web of life (ecosystem) of the mountain, and surrounding area is also fragmented. In a healthy mountain, rainwater percolates into the mountain until it hits the impermeable layers of coal which funnels water out of the mountain, helping to form critical headwaters of watersheds. Tennessee currently allows two main forms of mountain top mining; steep slope strip mining (which includes contour mining) and area mining (which includes cross-ridge mining).
Steep slope mining involves several subtypes of mining. In Tennessee, mining operations are required to “restore the land to the approximate original contour (AOC)”, through the use of backfill. The company, however, may submit an appeal for a variance, allowing them to leave the site with a flattened or near-flat top. Steep slope mining operations remove all or a large portion of the coal seam or seams running through the upper sections of a mountain. Such operations include contour mines and mountaintop removal mines with variances from AOC. Currently, there are no long-term scientific studies on the geologic stability of re-contoured mountains and ridges. “For all we know, reclaimed sites could act like giant sponges and blow out years down the line,” stated a Tennessee Department of Environment and Conservation official.
Contour mines occur in mountains or rolling hills where it is uneconomical or unfeasible to remove all of the overburden from a particular coal seam. This mining is limited to the side of a mountain or to the end of a ridge line. 
Contour mining begins with construction of roads and clear-cut logging of the mine site. A bench is excavated in the mountain at the coal seam elevation to create room for the mining equipment. The overburden (“spoil”) is then loaded into large haul trucks and transported to a fill or disposal area (Figure 1). Once the coal seam is reached, the coal is removed and the process may continue to the next layer. Previous mining practices left large highwalls carved into the mountain sides. Contour mining extracts coal from unmined mountains or previously highwalled mines, carving deeper into the mountainside before backfilling and re-contouring during restoration efforts (Figure 2). Much of the mining spoil is used to backfill the mined area to a terraced “approximation” of a mountain contour, making the mountain look like a layer cake—a cake built with rubble and mining waste.
Cross-ridge mining is a form of area mining that blows off the top of the mountain. Area mining takes place over a range of slopes or grades and is not restricted to the side of a mountain or ridgeline, producing mines across topography rather than around it. 
Area mines generally have larger working areas than contouring mines and may employ large, earth-moving machines for coal production. Cross-ridge mining progresses parallel to the long axis of a ridge, moving vertically down through the top of the mountain, layer by layer. Although both remove mountain tops, the main difference between cross-ridge mining and what is commonly called mountaintop removal mining (MTR) is the method of dealing with the overburden. The MTR mining (currently practiced in West Virginia, Virginia and Kentucky) converts lush Appalachian mountains into a level plateau like the mesas of the southwest, or into gently rolling pastures with no resemblance to the original contour. MTR mining also destroys adjacent valleys by filling them with what was once the tops of the mountains. Although mountain top mines in Tennessee are not supposed to do valley fills, they occasionally do “hollow” fills, destroying critical headwaters.
