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Coal mine bump
A coal mine bump (also called a bump, a mine bump, or a mountain bump) is a seismic jolt occurring within a mine, often due to the explosive collapse of a wall or one or more support pillars,〔(Energy Citations Database (ECD) - - Document #7218222 )〕 sometimes called a rock burst. These pillars are left in place during room and pillar mining, where an original narrow passage is dug and then substantially widened as ore is removed, creating open rooms with support pillars left in place. As the coal is extracted, the pressure is redistributed onto the pillars and can increase to the extent that the pillar explodes like a hand grenade, shooting coal and rock at lethal speeds.
In the eastern United States' coalfields, bumps are more likely when the overburden is at least 500 feet (150 m); where a strong, overlying stratum, such as sandstone, occurs near the coalbed; and with a strong, inflexible floor. In the United States, the number of deaths from bumps had dropped off dramatically since the early 1990s, but fatalities are more common in the West where mines often run deeper. Bumps are three times more likely in room-and-pillar mines, and are even more common in mines that do retreat mining,〔 in which the pillars are removed as the miners retreat towards the mine entrance with the intent of allowing an orderly collapse of the mine.〔(Coal Mine Bumps: Five Case Studies in the Eastern United States ). National Institute for Occupational Safety and Health. Accessed March 26, 2009.〕
==Incidents==
The Springhill Mining Disaster was a bump that occurred in Springhill, Nova Scotia, Canada on October 23, 1958.
Debate over the cause of the August 6, 2007, Crandall Canyon Mine disaster, which took place 1,800 feet beneath the surface, raised public awareness about coal mine bumps.〔("Rescue Halted at Mine After 3 Killed and 6 Injured", ''New York Times'', August 9, 2007, retrieved August 17, 2007 )〕 Seismologists at the University of Utah and the University of California, Berkeley concluded that an associated 3.9 magnitude temblor was likely caused not by an earthquake, but by the collapse itself.〔("Seismologists confirm Utah mine collapse probably caused temblor", U.S. Berkeley press release, August 9, 2007, retrieved August 17, 2007 )〕 The mine's owner, Robert E. Murray, adamantly disagreed.〔("Owner of Utah mine is a famously combative figure ). ''Boston Herald''. Retrieved on August 10, 2007.〕
抄文引用元・出典: フリー百科事典『 ウィキペディア（Wikipedia）』
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