A new mapping tool uses satellite imagery to reveal where mountaintop coal mining is underway in Appalachia, going back more than three decades. Graphic: Christian Thomas / SkyTruth

DURHAM, North Carolina, 25 July 2018 (Duke Today) – The coal industry may have declined in the last decade because of the rise of cheap natural gas, but a coal mining method called mountaintop removal is still taking place, particularly in central Appalachia.

A new web-based mapping tool shows, in more detail than ever before, the land laid bare by mountaintop coal mining in central Appalachia each year, going back more than three decades.

The tool uses satellite imagery to identify and map the annual extent of mining activity across a four-state area including portions of Kentucky, Tennessee, Virginia, and West Virginia.

In the journal PLOS ONE, researchers estimate that between 1985 and 2015, an average of 21,000 acres was converted to bare earth and rubble in central Appalachia each year – an area about half the size of Washington, D.C.

This analysis places the total estimate since the 1970s at about 1.5 million acres. “That is an area 18 percent larger than the state of Delaware, and only 3 percent smaller than Everglades National Park,” said first author Andrew Pericak, who conducted the research in the lab of biology professor Emily Bernhardt at Duke University.

Mountaintop mining is a form of surface coal mining in which coal companies clear the forest from a hilltop, then use explosives and heavy machinery to blast and dig through the soil and bedrock and expose the layers of coal underneath. The leftover rock and debris is pushed into adjacent valleys, burying streams under hundreds of meters of rubble called “valley fill.”

Advocates say the process allows mining companies to harvest shallow seams of coal they can’t get at via traditional underground mining. But growing scientific evidence suggests it also destroys forests, fills the air with harmful dust and contaminates nearby streams.

Determining the timing and extent of mining activity is crucial to assessing and mitigating these environmental and human impacts, said co-author Matthew Ross, previously at Duke and now a post-doctoral researcher at the University of North Carolina at Chapel Hill.

But reliable, up-to-date estimates of mining's footprint are hard to come by. In any given year, a mining company may only be operating within a portion of the area shown on their mining permit. Previous efforts have mapped surface mining in Appalachia using satellite imagery, but these maps haven't been updated since 2006, and only give a snapshot of mining every 10 years, rather than year-to-year.

The tool developed by Duke researchers, working with partners at the nonprofit organizations SkyTruth and Appalachian Voices, reveals where mountaintop mining is underway on a finer time scale, and makes it easier to keep the data current.

The team used Google’s Earth Engine cloud-computing platform to process U.S. government satellite images of visible and invisible light reflected from the Earth’s surface, taken over 31 consecutive years in a 74-county area.

Each pixel in 10,240 satellite images, going back to 1985, was analyzed by a computer algorithm that used reflectance data to determine the “greenness” of each small square of the image, which represents a 100-by-100-foot square of Earth. 

A collection of pixels that appeared largely devoid of vegetation and wasn’t part of a city, road or body of water was labeled as an area where mining was likely occurring that year, with at least 83 percent accuracy in any given year.

“It just took a matter of minutes to output the data set,” Pericak said. “It’s a huge time save.”

Aerial view of a mountaintop removal coal mining site in West Virginia. Photo: Kent Kessinger / Appalachian Voices

The team also combined their mine area estimates with previously published data on coal production. In the 1980s and 1990s, they found, every 100 square feet of land in the region yielded one ton of coal. By 2010, however, coal companies needed to clear and blast about 160 square feet per ton, and by 2015, it took more than 300 square feet.

“It takes more land to get the same amount of coal than it had in the past,” Pericak said.

The results are consistent with what geologists since the mid-1990s have forewarned -- that as thicker, more accessible layers of coal are mined out, the ratio of waste rock and soil to coal will increase, along with operating costs, Ross said.

Senior co-author Emily Bernhardt says the updated maps will help researchers come up with more accurate estimates of the costs and benefits of mountaintop mining, and how it compares with other forms of resource extraction.

“Any scientist interested in studying the impacts of mountaintop mining can now see exactly where mines are in the landscape and how long those impacts have been active,” said Bernhardt, who is using the data to understand more precisely how mountaintop mining affects water quality, how far the effects extend downstream and how long they persist.

Indiana University professor Michael Hendryx, who was not involved in the study, has been using the updated maps to assess air pollution exposure and other health effects in people living near active mining sites, compared with people living farther away.

“It also provides the public a better opportunity for monitoring mining operations to ensure they are adhering to the conditions in their permits,” said co-author Christian Thomas of SkyTruth. “Any new problems that crop up could potentially be acted on and corrected more effectively with this annual look at the region.”

Thomas says SkyTruth plans to use the data to measure the effectiveness of reclamation efforts after mining has stopped. “This is the key to helping the region recover from this legacy of mining and transition to a non-mining future,” Thomas said.

The data and computer code are free for anyone to use, and future mining activity can be quickly added to the dataset as new satellite imagery becomes available, Pericak said.

Watch a timeline of active mining for any location in central Appalachia or time period between 1985 and 2015 at http://skytruthmtr.appspot.com/.

Other authors include David Kroodsma, Yolandita Franklin and John Amos of SkyTruth; Matthew Wasson of Appalachian Voices, Nicholas Clinton of the Google Earth Engine Team and David Campagna of West Virginia University.

This research was supported by the Foundation for the Carolinas, the National Science Foundation Graduate Research Fellowship Program, the National Science Foundation Earth Sciences Hydrological Sciences (1417405), the Cornell Douglas Foundation, and the Wallace Genetic Foundation.

Mapping Mountaintop Coal Mining’s Yearly Spread in Appalachia


Active mining, cumulative mining, and coal production over time in Central Appalachia. “Active Mining” (A) means any land area detected by our model as likely mine for the given year; “Cumulative Mining” (B) is the non-duplicative summation of active mine area over time; this sum includes mine areas identified from pre-1976 through 1984 from the MTM2009 data. “Newly-Mined Areas” (C) is the land area that was first converted into a mine in the given year. “Surface Coal Production” (D) data is from the Mine Safety and Health Administration rather than our model; we present it here for comparison. Graphic: Pericak, et al., 2018 / PLOS ONE

ABSTRACT: Surface mining for coal has taken place in the Central Appalachian region of the United States for well over a century, with a notable increase since the 1970s. Researchers have quantified the ecosystem and health impacts stemming from mining, relying in part on a geospatial dataset defining surface mining’s extent at a decadal interval. This dataset, however, does not deliver the temporal resolution necessary to support research that could establish causal links between mining activity and environmental or public health and safety outcomes, nor has it been updated since 2005. Here we use Google Earth Engine and Landsat imagery to map the yearly extent of surface coal mining in Central Appalachia from 1985 through 2015, making our processing models and output data publicly available. We find that 2,900 km2 of land has been newly mined over this 31-year period. Adding this more-recent mining to surface mines constructed prior to 1985, we calculate a cumulative mining footprint of 5,900 km2. Over the study period, correlating active mine area with historical surface mine coal production shows that each metric ton of coal is associated with 12 m2 of actively mined land. Our automated, open-source model can be regularly updated as new surface mining occurs in the region and can be refined to capture mining reclamation activity into the future. We freely and openly offer the data for use in a range of environmental, health, and economic studies; moreover, we demonstrate the capability of using tools like Earth Engine to analyze years of remotely sensed imagery over spatially large areas to quantify land use change.

Mapping the yearly extent of surface coal mining in Central Appalachia using Landsat and Google Earth Engine

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