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Supervolcano
A supervolcano is any volcano capable of producing a volcanic eruption with an ejecta mass greater than 1015 kg. Supervolcanoes can occur when magma in the mantle rises into the crust from a hotspot but is unable to break through the crust, and pressure builds in a large and growing magma pool until the crust is unable to contain the pressure (this is the case for the Yellowstone Caldera). They can also form at convergent plate boundaries (for example, Toba). Large igneous provinces can cover huge areas with lava and volcanic ash, causing long-lasting climate change (such as the triggering of a small ice age or global warming), which can threaten species with extinction.
== Terminology ==
The origin of the term "supervolcano" is linked to an early 20th-century scientific debate about the geological history and features of the Three Sisters volcanic region of Oregon in the United States. In 1925, Edwin T. Hodge suggested that a very large volcano, which he named Mount Multnomah, had existed in that region. He believed that several peaks in the Three Sisters area are the remnants left after Mount Multnomah had been largely destroyed by violent volcanic explosions, similar to Mount Mazama.〔Harris, Stephen (1988) ''Fire Mountains of the West: The Cascade and Mono Lake Volcanoes'', Missoula, Mountain Press.〕 In 1948, the possible existence of Mount Multnomah was ignored by volcanologist Howel Williams in his book ''The Ancient Volcanoes of Oregon''. The book was reviewed in 1949 by another volcanologist, F. M. Byers Jr.〔Byers, Jr., F. M. (1949) (''Reviews: The Ancient Volcanoes of Oregon by Howel Williams'' ), The Journal of Geology, volume 57, number 3, May 1949, page 324. Retrieved 2012-08-17.〕 In the review, Byers refers to Mount Multnomah as a supervolcano.〔(''supervolcano, n.'' ) Oxford English Dictionary, third edition, online version June 2012. Retrieved on 2012-08-17.〕 Although Hodge's suggestion that Mount Multnomah is a supervolcano was rejected long ago, the term "supervolcano" was popularised by the BBC popular science television program ''Horizon'' in 2000 to refer to eruptions that produce extremely large amounts of ejecta.〔(Supervolcanoes ). Bbc.co.uk (2000-02-03). Retrieved on 2011-11-18.〕〔(USGS Cascades Volcano Observatory ). Vulcan.wr.usgs.gov. Retrieved on 2011-11-18.〕
Volcanologists and geologists do not refer to "supervolcanoes" in their scientific work, since this is a blanket term that can be applied to a number of different geological settings. Since about 2000, however, the term has been used by professionals for communicating science to the public. The term ''megacaldera'' is sometimes used for caldera supervolcanoes, such as the Blake River Megacaldera Complex in the Abitibi greenstone belt of Ontario and Quebec, Canada. Eruptions that rate VEI 8 are termed "super eruptions". Though there is no well-defined minimum explosive size for a "supervolcano", there are at least two types of volcanic eruptions that have been identified as supervolcanoes: large igneous provinces and massive eruptions.〔
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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