Editing Longwall mining (section)

==History==
[[File:LongwallOld.png|thumb|250px|right|Plan of longwall mine before conveyors – the hoist is at the center of the central pillar.]]
The basic idea of longwall mining was developed in [[England]] in the late 17th century, although it may have been anticipated in the pre-industrial era by a similar technique utilized by the [[Hopi]] of Northeastern Arizona in the 14th century.<ref>{{cite book |last= Bullard Jr. |first= William Rotch |date= 1962 |title= The Cerro Colorado Site and Pithouse Architecture in the Southwestern United States Prior to A.D. 900 |url=https://hdl.handle.net/2027/uc1.31210001230687 |location= Cambridge, Massachusetts, USA |publisher= The Peabody Museum |page=vi}}</ref> Miners undercut the coal along the width of the coal face, removing coal as it fell, and used wooden props to control the fall of the roof behind the face. This was known as the [[Shropshire]] method of mining.<ref>[http://tonto.eia.doe.gov/ftproot/coal/tr0588.pdf Longwall Mining] {{webarchive|url=https://web.archive.org/web/20090817012119/http://tonto.eia.doe.gov/FTPROOT/coal/tr0588.pdf |date=2009-08-17 }}, Office of Coal, Nuclear, Electric and Alternate Fuels, U.S. Department of Energy, March 1995, pp. 9–10.</ref> While the technology has changed considerably, the basic idea remains the same, to remove essentially all of the [[coal]] from a broad coal face and allow the roof and overlying [[Rock (geology)|rock]] to collapse into the void behind, while maintaining a safe working space along the face for the miners.

Starting around 1900, mechanization was applied to this method. By 1940, some referred to longwall [[mining]] as "the conveyor method" of mining, after the most prominent piece of machinery involved.<ref>A. Paxton, J. A. Biggs, [http://www.pastperfect.org.uk/sites/woodhorn/album/index.html Ten Minutes in a Coal Mine], 1940, pp. 16–24</ref> Unlike earlier longwall mining, the use of a [[conveyor belt]] parallel to the coal face forced the face to be developed along a straight line. The only other machinery used was an [[electric]] cutter to undercut the coal face and electric [[drill]]s for blasting to drop the face. Once dropped, manual labor was used to load coal on to the conveyor parallel to the face and to place wooden roof props to control the fall of the roof.

Such low-technology longwall mines continued in operation into the 1970s. The best known example was the New Gladstone Mine near [[Centerville, Iowa]], "one of the last advancing longwall mines in the United States".<ref>{{cite book
| title = Iowa's geological past: three billion years of earth history
| last = Anderson
| first = Wayne I.
| year = 1998
| publisher = University of Iowa Press
| location = Iowa City
| isbn = 0-87745-639-9
| page = 258
| url = https://books.google.com/books?id=D2kzQ5RC4JMC&q=%22New+Gladstone+Mine%22+Iowa&pg=PA428
| accessdate = 2010-06-05}}</ref> This longwall mine did not use a conveyor belt, instead relying on ponies to haul coal tubs from the face to the [[Slope mining|slope]] where a hoist hauled the tubs to the surface.<ref>{{cite book
| last= Brick
| first= Greg A.
| title= Iowa Underground: a guide to the state's subterranean treasures
| ol= 3314195M
| year= 2004
| publisher= Trails Books
| location=  Black Earth, Wis.
| isbn= 978-1-931599-39-9
| pages= 119–120
}}</ref><ref>''The Last Pony Mine'', a documentary film, Les Benedict, director, Steve Knudston, producer, 1972.  Available on YouTube in 3 parts [https://www.youtube.com/watch?v=O0NZRSDoqCk part 1][https://www.youtube.com/watch?v=NsbS4y8vIFU part 2][https://www.youtube.com/watch?v=t80NFheqwfo part 3]</ref>

Longwall mining has been extensively used as the final stage in mining old [[room and pillar]] mines. In this context, longwall mining can be classified as a form of [[retreat mining]].