Volcanic Explosivity Index
The Volcanic Explosivity Index (VEI) was devised by Chris Newhall of the U.S. Geological Survey and Steve Self at the University of Hawaii in 1982 to provide a relative measure of the explosiveness of volcanic eruptions. Volume of products, eruption cloud height, and qualitative observations (using terms ranging from "gentle" to "mega-colossal") are used to determine the explosivity value. The scale is open-ended and ranges from 0, for non-explosive eruptions (less than 104 cubic metres of tephra ejected), to 8, for mega-colossal explosive eruptions that can eject 1012 cubic metres of tephra and have a cloud column height of over 25 km. Each interval on the scale represents a ten-fold increase in observed eruption criteria. Values higher than 8 can be determined if needed. One weakness of the VEI is that it does not take into account of the density of erupted material; ash, volcanic bombs, and ignimbrite are all treated alike. In addition, the VEI does not take into account the magnitude of power output of an eruption.
Count of historic eruptions based on 1994 figures maintained by the Global Volcanism Program of the Smithsonian Institution
See also Nevado del Ruiz, 1985 (VEI = 3) Mount St. Helens, 1980 eruption (VEI = 5) Krakatoa, 1883 (VEI = 6) Novarupta, 1912 (VEI = 6) Mount Tambora, 1815 (VEI = 7) Long Valley Caldera (VEI = 7) Yellowstone (VEI = 8)
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