Earthshots: Satellite Images of Environmental Change

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» Powder River Basin, Wyoming, USA

Every day, 100 empty trains enter Wyoming. They leave fully loaded with coal. The United States has the largest coal reserves in the world, and much of it lies in the Powder River Basin (PRB) in Wyoming and Montana. The PRB, which lies between the Black Hills in South Dakota and the Bighorn Mountains in Wyoming, produced 43% of the nation’s coal in 2019.

According to a study by the U.S. Geological Survey, the PRB contains 25 billion tons of economically recoverable coal. This does not mean it’s all mineable. The amount of economically recoverable coal can change based on mining costs and coal prices, which change based on market conditions. Nevertheless, the region has a lot of coal that is very accessible.

The Black Thunder Mine and the North Antelope Rochelle Complex are two of the largest open-pit mines in the PRB. They lie within the Thunder Basin National Grassland. These mines have been expanding over the past few decades, and the land change is evident in this time series of Landsat images.

Map of the featured area.

The Black Thunder Mine, shown in the series of Landsat images on the left, has sent 2.2 billion tons of coal to U.S. power plants since 1977. It produces 4 tons of coal per second.

The images show the expansion of the open-pit mining operations at Black Thunder. The black lines are the coal seams, the layers of coal that formed over time and lie under the land surface. Lighter straight lines are stepped benches that allow trucks to drive in and out of the mine.


Coal Formation in the PRB

The North Antelope Rochelle Complex is the most productive of the PRB mines. In 2018, the mine sold 98.4 million tons of coal. In 2017, it accounted for 13.1% of U.S. coal production. It began operations in 1983, and the series of Landsat images shows the progression of this mine since 1984.


Clean Coal

 Coal Facts


The mining process that takes place in the PRB is called surface mining. First, the topsoil is removed. The material above the coal (overburden in mining jargon) is then removed to expose the coal. The overburden is placed into a previously mined pit.

The exposed coal is then scooped out. Rocks, ash, sulfur, and other contaminants are cleaned out of the coal. Blasting and crushing reduces the coal to smaller pieces that can be loaded onto trains for transport. Trains bring the coal to power plants throughout the country.

The Surface Mining Control and Reclamation Act (SMCRA) requires mining companies to reclaim the mined land. The mined land is filled in with overburden, and the topsoil is replaced. Native seeds are planted on the reclaimed land. The whole process is overseen by environmental engineers and state and federal agencies to ensure compliance with laws. Lands disturbed by coal mining must be restored to a condition that can support the uses it could support before mining (or even make the land better).

In the close-up images, the mined land seems to move over time. As the mining and beginnings of the reclamation process take place, we can see the digging and backfilling occurring.

(See the animations in the subsection called "Animations" to see more images and to see this process happen over the 30-year time period.)

The PRB has become about more than just coal. Oil production is also increasing. Similar to the Bakken Formation in North Dakota, new technologies are allowing oil to be more economically recoverable.

Since 2009, hundreds of oil wells have been drilled in the PRB. In the second half of 2010, 219 drilling permits were received. In the first half of 2014, 1,161 permits were received.

These images show the region just west of the Black Thunder Mine. The 2014 image looks like a messy dot-to-dot drawing. The light dots, connected by crooked lines, are oil wells and the roads that lead to them.

The coal mines in the PRB advance quickly enough to see a lot of change from year to year. Two animations available here show the annual change of the mines in the regions.

The first animation shows almost one image per year back to 1984 of both the Black Thunder and North Antelope Rochelle Complex Mines. The second one listed is a close-up of the North Antelope Rochelle Complex and covers the same time period.

The date of each image appears in the lower right corner.

  1. PRB coal mines: 1984–2018
  2. North Antelope Rochelle Complex Mines: 1984–2018

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