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List of largest volcanic eruptions
In a volcanic eruption, lava, tephra (volcanic bombs, lapilli, and ash), and various gases are expelled from a volcanic vent or fissure. While many eruptions only pose dangers to the immediately surrounding area, Earth's largest eruptions can have a major regional or even global impact, with some affecting the climate and contributing to mass extinctions. Volcanic eruptions can generally be characterized as either explosive eruptions, sudden ejections of rock and ash, or effusive eruptions, relatively gentle outpourings of lava.〔(【引用サイトリンク】url=http://www.geolsoc.org.uk/gsl/site/GSL/lang/en/page3599.html )〕 A separate list is given below for each type.
All of the eruptions listed below have produced at least of lava and tephra; for explosive eruptions, this corresponds to a Volcanic Explosivity Index (or VEI) of 8.〔(【引用サイトリンク】url=http://www.geology.sdsu.edu/how_volcanoes_work/Variability.html )〕 They are at least a thousand times larger than the 1980 eruption of Mount St. Helens, which produced only of material, and at least six times larger than the 1815 eruption of Mount Tambora, the largest eruption in recent history, which produced of volcanic deposits.
There have probably been many such eruptions during Earth's history beyond those shown in these lists. However erosion and plate tectonics have taken their toll, and many eruptions have not left enough evidence for geologists to establish their size. Even for the eruptions listed here, estimates of the volume erupted can be subject to considerable uncertainty.〔
==Explosive eruptions==
In explosive eruptions, the eruption of magma is driven by the rapid release of pressure, often involving the explosion of gas previously dissolved within the material. The most famous and destructive historical eruptions are mainly of this type. An eruptive phase can consist of a single eruption, or a sequence of several eruptions spread over several days, weeks or months. Explosive eruptions usually involve thick, highly viscous, silicic or felsic magma, high in volatiles like water vapor and carbon dioxide. Pyroclastic materials are the primary product, typically in the form of tuff. Eruptions the size of that at Lake Toba 74,000 years ago, at least , or the Yellowstone eruption 620,000 years ago, around , occur worldwide every 50,000 to 100,000 years.〔〔Certain felsic provinces, such as the Chon Aike province in Argentina and the Whitsunday igneous province of Australia are not included in this list since they are composed of many separate eruptions that have not been distinguished.〕
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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