Volcanic Explosivity Index
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The Volcanic Explosivity Index (VEI) was devised by Chris Newhall of the US Geological Survey and Stephen 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 with the largest volcanoes in history given magnitude 8. A value of 0 is given for non-explosive eruptions, defined as less than 10,000 m3 (350,000 cu ft) of tephra ejected; and 8 representing a mega-colossal explosive eruption that can eject 1.0×1012 m3 (3.5×1013 cu ft) of tephra and have a cloud column height of over 50 km (31 mi). The scale is logarithmic, with each interval on the scale representing a tenfold increase in observed ejecta criteria, with the exception of between VEI 0, VEI 1 and VEI 2.
Ash, volcanic bombs, and ignimbrite are all treated alike. Density and vesicularity (gas bubbling) of the volcanic products in question is not taken into account. In contrast, the DRE (Dense-Rock Equivalent) is sometimes calculated to give the actual amount of magma erupted. Another weakness of the VEI is that it does not take into account the power output of an eruption, which makes it extremely difficult to determine with prehistoric or unobserved eruptions.
With indices running from 0 to 8, the VEI associated with an eruption is dependent on how much volcanic material is thrown out, to what height, and how long the eruption lasts. The scale is logarithmic from VEI 2 and up; an increase of 1 index indicates an eruption that is 10 times as powerful. As such there is a discontinuity in the definition of the VEI between indices 1 and 2. The lower border of the volume of ejecta jumps by a factor of 100 from 10,000 to 1,000,000 m3 (350,000 to 35,000,000 cu ft) while the factor is 10 between all higher indices.
|0||< 10,000 m³||Hawaiian||effusive||< 100 m||constant||negligible||none||Kīlauea, Piton de la Fournaise, Erebus|
|1||> 10,000 m³||Hawaiian / Strombolian||gentle||100–1000 m||daily||minor||none||Stromboli, Nyiragongo (2002)|
|2||> 1,000,000 m³||Strombolian / Vulcanian||explosive||1–5 km||weekly||moderate||none||Galeras (1993), Mount Sinabung (2010)|
|3||> 10,000,000 m³||Vulcanian / Peléan||severe||3–15 km||few months||substantial||possible||Nevado del Ruiz (1985), Soufrière Hills (1995)|
|4||> 0.1 km³||Peléan / Plinian||cataclysmic||10–25 km||≥ 1 yr||substantial||definite||Mount Pelée (1902), Eyjafjallajökull (2010)|
|5||> 1 km³||Plinian||paroxysmal||20–35 km||≥ 10 yrs||substantial||significant||Mount Vesuvius (79 CE), Mount St. Helens (1980)|
|6||> 10 km³||Plinian / Ultra-Plinian||colossal||> 30 km||≥ 100 yrs||substantial||substantial||Krakatoa (1883), Mount Pinatubo (1991)|
|7||> 100 km³||Ultra-Plinian||super-colossal||> 40 km||≥ 1,000 yrs||substantial||substantial||Mazama (c. 5600 BCE), Thera (c. 1620 BCE), Tambora (1815)|
|8||> 1,000 km³||Supervolcanic||mega-colossal||> 50 km||≥ 10,000 yrs||substantial||substantial||Yellowstone (640,000 BCE), Toba (74,000 BCE), Taupo (24,500 BCE)|
A total of 47 eruptions of VEI 8 magnitude or above, ranging in age from Ordovician to Pleistocene, have been identified, of which 42 occurred in the past 36 million years. The most recent is Lake Taupo's Oruanui eruption, 26,500 years ago, which means that there have not been any Holocene (within the last 10,000 years) eruptions with a VEI of 8. There have been at least 5 identified Holocene eruptions with a VEI of 7. There are also 58 plinian eruptions, and 13 caldera-forming eruptions, of large, but unknown magnitudes. There are likely many other eruptions that are not identified.
List of eruptions 
- List of largest volcanic eruptions
- List of large volcanic eruptions
- List of large volcanic eruptions of the 19th Century
- List of large volcanic eruptions of the 20th Century
- List of large volcanic eruptions of the 21st Century
See also 
- Newhall, Christopher G.; Self, Steve (1982). "The volcanic explosivity index (VEI): An estimate of explosive magnitude for historical volcanism". Journal of Geophysical Research 87 (C2): 1231–1238. Bibcode:1982JGR....87.1231N. doi:10.1029/JC087iC02p01231.
- VEI (Volcanic Explosivity Index), Global Volcanism Program, Smithsonian National Museum of Natural History
- Mason, Ben G.; Pyle, David M.; Oppenheimer, Clive (2004). "The size and frequency of the largest explosive eruptions on Earth". Bulletin of Volcanology 66 (8): 735–748. Bibcode:2004BVol...66..735M. doi:10.1007/s00445-004-0355-9.
- VEI glossary entry from a USGS website
- How to measure the size of a volcanic eruption, from The Guardian
- The size and frequency of the largest explosive eruptions on Earth, a 2004 article from the Bulletin of Volcanology
- List of Large Holocene Eruptions (VEI > 4) from the Smithsonian Global Volcanism Program
- VEI (Volcanic Explosivity Index) from the Global Volcanism Program of the Smithsonian National Museum of Natural History