Strip and surface mining

DEFINITION: Mining methods in which rock and soil are removed to enable extraction of the substance being mined

Surface-mining methods make possible the extraction of minerals and coal from narrow seams that could not feasibly be mined using underground techniques. These methods, however, cause many different forms of damage to the environment, radically changing landscapes, blocking streams, destroying habitats, and polluting waterways.

Humans have long scraped away the surface of the land to get at the minerals and other materials underneath. For centuries this type of mining created scars on the landscape but rarely did major harm to the environment. In the twentieth century, however, surface mines became much larger and began to cause lasting environmental degradation. In some cases is the only feasible way to extract very narrow seams of or minerals. In addition, surface mining tends to be less hazardous for miners than underground mining and requires fewer and often less skilled workers, reducing costs. Massive surface mining is a characteristic of modern industrial society.

Open-Pit Mining

Minerals have long been mined using underground tunnels, but it is often more feasible to remove the dirt and rocks covering deposits (the overburden) to get at them. In some cases the ore grade is so low that extensive treatment with crushers and chemicals (such as the cyanide leach process used with gold) is required. Open-pit mines are gradually expanded and deepened over time. The sides of such a mine are cut in a spiral, with benches ringing the sides so that trucks can access the material at the bottom of the pit. As the mine is deepened, often becomes a problem, requiring pumping or other forms of water control to keep the mine from filling with water.

Shallow open-pit mines (often called quarries) are used to extract granite, limestone, gypsum, and clay. Some gemstones, such as diamonds, are mined in open pits such as was done in Kimberly, South Africa. Copper, nickel, iron ore, gold, and uranium are some of the minerals mined in this fashion. One of the largest open-pit mines in the world, the Hull-Rust-Mahoning Mine in Hibbing, Minnesota, has been in operation since 1895. This iron mine is 4.8 kilometers (3 miles) long, 3.2 kilometers (2 miles) wide, and 163 meters (535 feet) deep.

Starting during the early twentieth century, large open-pit copper mines began to be opened in the American West. One of the earliest was the Bingham Canyon Mine in Utah, which has been in operation since 1906. The pit of this mine covers 770 hectares (1,900 acres) and is 1.2 kilometers (0.75 miles) deep and 4 kilometers (2.5 miles) wide. By the early twenty-first century the mine had produced more than 17 million tons of copper, 190 million ounces of silver, 23 million ounces of gold, and 850 million pounds of molybdenum.

Bingham Canyon Mine is the largest human-made excavation in the world, but other copper mines are also quite large, such as the Chuquicamata in Chile, the Nchanga mines in Zambia, and the Grasberg mine in Indonesia. Although copper is a major product of these mines, some also produce other minerals, such as gold and silver. Indeed, the Grasberg mine is the largest gold mine and one of the largest copper mines in the world. Other open-pit mines, such as Kumtor in Kyrgyzstan, produce gold and uranium. Massive open-pit mines are also found in Russia, Australia, Canada, Peru, Mongolia, and Namibia. Some of these mines exist in environmentally fragile surroundings; Kumtor, for instance, is more than 4,000 meters (14,000 feet) above sea level on a high plateau, and Grasberg is located on a mountaintop near rare equatorial glaciers and in a region subject to earthquakes that produce large landslides.

Open-pit mining produces several environmental hazards. The removed at an open-pit mine, which often contains hazardous chemicals, must be placed nearby. As the mine expands, it consumes nearby land. The Berkeley Pit, for example, consumed several neighborhoods in Butte, Montana. In addition, the processing of the material taken from an open-pit mine often involves treating it with acid, which leads to extensive runoff. The acidic runoff, dissolved copper, and other materials from processing at the Grasberg mine, for example, wash into two rivers that are the water sources for several communities, and some of it ultimately reaches the ocean, a situation that will continue long after the mine is closed.

When mining ceases at an open-pit mine, the pit often becomes flooded, producing a large lake that is highly acidic. The Berkeley Pit in Montana provides an example of this process. The mine opened in 1955 and closed in 1982. Since 1982 water has filled the mine to within 46 meters (150 feet) of the natural level. The water contains several heavy metals, such as arsenic and cadmium, and is highly acidic (a of 2.5). A water diversion project has been established to keep the acidic water in the Berkeley Pit from entering the water supplies of Butte and surrounding communities. In 1983, the US Environmental Protection Agency listed the Berkeley Pit as a site that required massive cleanup efforts under the provisions of the Comprehensive Environmental Response, Compensation, and Liability Act of 1980, commonly known as Superfund; as of May 2014, remediation and restoration efforts were ongoing.

Strip Mining

The process of mining shallow deposits of coal and tar sands often involves the removal of the overburden. In the most common form of strip mining, the overburden is removed and placed in the excavation left by the previous strip. Contour mining involves removing land along the contour of the land and usually produces terraces on a mountainside. Massive pieces of equipment are used in strip mining, such as draglines, which remove the surface layer, and earthmovers, often two stories tall, which move the surface or coal.

Coal is strip-mined around the world. In the United States strip mining is used to remove surface coal seams in all parts of the country. The largest US strip mines are found in the Powder River basin in northeast Wyoming and southeastern Montana. Unlike coal in other parts of the country, such as West Virginia, the Powder River coal lies close to the surface. The Powder River coal deposits are some of the largest in the world. However, as of May 2024, the Biden administration ended coal leasin in the Powder River basin to protect human health and the environment.

As energy companies seek out additional sources of oil, oil-impregnated sands, known as oil sands or tar sands, are increasingly seen as sources of oil. Rising oil prices made it cost effective to, in essence, mine oil. One of the largest deposits of tar sands in the world is found in the Athabasca River basin in Alberta, Canada. In addition to endangering a fragile environment, the strip mining of these tar sands requires large amounts of energy to “crack” the oil and remove it from the sand.

Mountaintop Removal

A variant on surface mining for coal that has come to be adopted in parts of West Virginia, Kentucky, and southern Ohio is mountaintop removal, a mining method in which explosives are used on mountainsides to remove the overburden, which is then pushed into adjoining valleys. This approach allows miners to reach deeper into the earth than does conventional strip mining. In some cases not only are whole mountains removed but also the remaining earth is excavated.

Mountaintop removal drastically changes landscapes as whole mountains are destroyed and valleys are filled with overburden. Streams are often buried in the process, and sometimes large lakes are created in what remains of the valleys; the water in such lakes is highly acidic and contains heavy metals. Critics of mountaintop removal point out that the plant and animal species that live in mountain valleys, some of which are quite rare, are endangered by this mining method. In parts of West Virginia and Kentucky the has been changed permanently as mountains have been leveled by mining. In the Appalachia region mountaintop removal has damaged the water sources of several communities. In addition, the explosions that are part of this kind of mining can be dangerous to local people and structures, and the sulfur compounds in the dust created by the explosions pose a health hazard.

The Surface Mining Control and Reclamation Act of 1977 requires that the owners of any surface-mined land in the United States restore the land after mining operations have ceased, but with mountaintop removal this is not completely possible, as large flat areas of land are created where mountains once existed. The of some of these areas has taken the form of the creation of golf courses or industrial sites.

Mining and Industrial Progress

Access to coal and to minerals such as copper and gold is essential for modern industrial society. Achieving this access cheaply is also an important ingredient for economic development. In some cases access helps to reduce environmental problems, such as the strip mining of the Powder River basin’s low-sulfur coal to replace high-sulfur coal and reduce emissions of sulfur dioxide into the atmosphere. Some surface-mining approaches seem to be the only economically feasible way of acquiring certain minerals or energy sources that are essential to industrial society.

Nonetheless, an important drawback to surface mining is the extensive environmental degradation that often occurs during the mining process and after mines have ceased operations. In addition to the environmental damage posed by mining itself, many sites where deposits of desirable minerals or coal are located are heavily timbered and must be cleared before mining can begin; such deforestation destroys plant and animal habitats, contributes to global warming, and leads to soil erosion. Mining companies often opt for the cheapest approaches to resource extraction, even though these approaches may produce higher levels of environmental harm than other approaches.

Some countries have placed extensive regulations on surface mining of all kinds, with the aim of limiting the environmental damage such mining can do, whereas regulations in other nations are minimal. In the United States, the Surface Mining Control and Reclamation Act requires that owners of surface mine sites reclaim the land at least to some degree when mining has ended. Other laws limit the damage that mining operations are allowed to do to streams and endangered species. Debates are ongoing, however, regarding how effective these laws have been, especially since the presidential administration of George W. Bush weakened the application of some of the laws.

The societal dilemma posed by surface mining is that such mining is essential for economic progress yet often results in environmental harm. Further, the costs of this harm are not always shared equitably—industrialized nations frequently profit from surface mining that is conducted in developing countries, which often bear most of the costs of the environmental damage.

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