Mountaintop coal mining is a major cause of land cover changes in the central Appalachian Mountains of the eastern United States. The landscape disturbance mountaintop mining causes is different from others (such as forestry, urbanization, or agriculture) in that it can extend deeply into the ground, disturbing even the bedrock. Landsat imagery from the 1970s has catalogued the changes.
These false color images show the natural landscape of the area: forested mountains are bright green, and numerous streams and valleys give the land a wrinkled appearance. Mining areas are pink, and reclaimed mining land is usually light green.
The reason for the large-scale change caused by this type of mining is that one ton of coal is extracted for every 16 tons of terrain displaced. In the mountainous Appalachian landscape, the displaced material ends up in river valleys. More than just the look of the landscape changes—the drainage network itself is altered.
First mined in the 19th century, low-sulfur Appalachian coal can be extracted relatively cost-effectively by the mountaintop removal process. This method allows almost all of the coal in a seam to be removed. Understanding the hydrologic changes brought on by this mining practice is key to the future of the communities in the region.
Appalachian coal lies underground in thin seams, too thin for underground mine shafts. The only way to extract the coal profitably is with surface mining.
Surface mining involves the removal of soil and rock (overburden in mining terminology) with explosives and heavy machinery to get at the coal. As much as 200–300 meters of overburden is removed. The removed material, also called mine spoils, is used to reconstruct the area after mining operations are done. The removed material takes up more volume and cannot simply be replaced (try digging a hole in your backyard and filling it back in and you’ll discover how this works).
The “excess spoils” must be dumped elsewhere. In Appalachian mountaintop mining, the excess is deposited into valleys. These valley fills are usually located next to—often downstream from—surface mines, burying headwater streams completely. The groundwater and surface waters from the mine often flow through these valley fills before discharging into streams.
Disturbed land is pink in these close-up images of a large mine about 20 miles southwest of Charleston, West Virginia. The natural color image from Sentinel-2 shows more detail in the same area. Active mining is bright in this Sentinel-2 image, and lighter green shades show some reclaimed land.
The Surface Mining Control and Reclamation Act of 1977 requires that mined lands be restored to an acceptable land cover. These images show some of the landscape returning to green after mining operations have moved on. But the contours of the land are not exactly the same as they were before mining started.
Rock debris from the removal of overburden cannot be piled as high or graded as steeply as the original mountaintop. The topography ends up being leveled—the mountains are lowered and valleys raised.
To avoid erosion during the reclamation process, soils are heavily compacted and then planted with fast-growing grasses. Trees are sometimes planted as well but do not grow back as quickly in this environment. Those grasses appear in these images as faded green or mottled with pink, compared to the bright green of the pre-mining dense forest.
In this type of landscape, more precipitation becomes runoff than it would be in a forest. Furthermore, species diversity can lag behind natural forests, even decades later. The Sentinel-2 close-up makes that clear. A mined area on the left side of the image has returned to green after it was bright pink starting in 1986 in the Landsat imagery. But the shade of green is not yet the same dark green as intact forest.
The effects on the hydrology in the region where mountaintop mining takes place is not well understood—how does this mining activity affect the movement and storage of water?
The EPA, in a 2011 report, explains that stream ecosystems are affected by mountaintop mining in five principal ways:
- Springs are permanently lost when buried under valley fill.
- Elevated levels of chemicals are found downstream.
- Degraded water quality in streams can be lethal to organisms.
- Selenium levels are elevated in the water, toxic to fish and birds.
- Fish communities are degraded.
One way hydrology changes is through the reclamation process. Heavy equipment compacts the soil, which inhibits water infiltration and natural succession. That is, the compacted soil doesn’t soak in water the same way as it did before when it was natural forest. Native trees do not grow well in this compacted soil, where rainfall runs off faster. Even when grasses are planted immediately during reclamation, runoff is increased in these areas.
Increased runoff can lead to more frequent downstream flooding. Some fill areas that have large volumes of crushed rock can actually increase watershed storage. But how and to what extent these areas control runoff are not clear.
Furthermore, groundwater samples from mined areas after reclamation have been found to contain more mine-derived chemicals than water from unmined areas. These chemicals (lead, aluminum, chromium, manganese, and selenium) would otherwise remain sealed up in the coal and rock. Water flowing through the valley fills picks up these chemicals and flows into the streams. Researchers have linked declines in stream biodiversity to an increase in these contaminants, affecting the freshwater species found there.
These changes in hydrology and water chemistry can impair downstream aquatic ecosystems. Landsat observations can help water resource managers better understand these changes.
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