Volcanic explosivity index

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VEI and ejecta volume correlation

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 (240 cubic miles) 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.[1]

Classification

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 35,310,000 cu ft) while the factor is 10 between all higher indices.

VEI Ejecta volume Classification Description Plume Frequency Tropospheric
injection		 Stratospheric
injection[2]		 Examples
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 Nyiragongo (2002), Raoul Island (2006)
2 > 1,000,000 m³ Strombolian / Vulcanian Explosive 1–5 km weekly moderate none Unzen (1792), Cumbre Vieja (1949), Galeras (1993), Sinabung (2010)
3 > 10,000,000 m³ Vulcanian / Peléan Catastrophic 3–15 km few months substantial possible Nevado del Ruiz (1985), Soufrière Hills (1995), Nabro (2011)
4 > 0.1 km³ Peléan / Plinian Cataclysmic 10–25 km ≥ 1 yr substantial definite Mayon (1814), Pelée (1902), Eyjafjallajökull (2010)
5 > 1 km³ Plinian Paroxysmic 20–35 km ≥ 10 yrs substantial significant Vesuvius (79), Fuji (1707), Mount Tarawera (1886), St. Helens (1980), Puyehue (2011)
6 > 10 km³ Plinian / Ultra-Plinian Colossal > 30 km ≥ 100 yrs substantial substantial Veniaminof (c. 1750 BC), Huaynaputina (1600), Krakatoa (1883), Novarupta (1912), Pinatubo (1991), Laki (1783)
7 > 100 km³ Ultra-Plinian Mega-colossal > 40 km ≥ 1,000 yrs substantial substantial Mazama (c. 5600 BC), Thera (c. 1620 BC), Samalas (Mount Rinjani) (1257), Tambora (1815), Taupo (180)
8 > 1,000 km³ Supervolcanic Apocalyptic > 50 km ≥ 10,000 yrs substantial substantial Yellowstone (640,000 BC), Toba (74,000 BP), Taupo (24,500 BC) La Garita Caldera (26.3 Ma)

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.[3] There have been at least five 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.

Limitations of VEI

Under the VEI, ash, lava, lava 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.

Although VEI is quite suitable for classifying the explosive magnitude of eruptions, the index is not as significant as sulphur dioxide emissions in quantifying their atmospheric and climatic impact, as a 2004 paper by Georgina Miles, Roy Grainger and Eleanor Highwood points out.

“Tephra, or fallout sediment analysis, can provide an estimate of the explosiveness of a known eruption event. It is, however, not obviously related to the amount of SO2 emitted by the eruption. The volcanic explosivity index (VEI) was derived to catalogue the explosive magnitude of historical eruptions, based on the order of magnitude of erupted mass, and gives a general indication as to the height the eruptive column reached. The VEI itself is inadequate for describing the atmospheric effects of volcanic eruptions. This is clearly demonstrated by two eruptions, Agung (1963) and El Chichón (1982). Their VEI classification separates them by an order of magnitude in explosivity, although the volume of SO2 released into the stratosphere by each was measured to be broadly similar, as shown by the optical depth data for the two eruptions.”[4]

Lists of large eruptions

2011 Puyehue-Cordón Caulle eruption 1980 eruption of Mount St. Helens 1912 eruption of Novarupta Yellowstone Caldera 1092 eruption of Santa María 1280 eruption of Quilotoa 1600 eruption of Huaynaputina 2010 eruptions of Eyjafjallajökull Yellowstone Caldera 1783 eruption of Laki 1477 eruption of Bárðarbunga Volcanic activity at Santorini Toba catastrophe theory Kuril Islands Kikai Caldera 1991 eruption of Mount Pinatubo Long Island (Papua New Guinea) 1815 eruption of Mount Tambora 1883 eruption of Krakatoa 2010 eruptions of Mount Merapi Billy Mitchell (volcano) Taupo Volcano Taupo Volcano Taupo Volcano Crater Lake
Clickable imagemap of notable volcanic eruptions. The apparent volume of each bubble is linearly proportional to the volume of tephra ejected, colour-coded by time of eruption as in the legend. Pink lines denote convergent boundaries, blue lines denote divergent boundaries and yellow spots denote hotspots.

See also

References

  1. ↑ Newhall, Christopher G.; Self, Stephen (1982). "The Volcanic Explosivity Index (VEI): An Estimate of Explosive Magnitude for Historical Volcanism" (PDF). Journal of Geophysical Research 87 (C2): 1231–1238. Bibcode:1982JGR....87.1231N. doi:10.1029/JC087iC02p01231.
  2. ↑ VEI (Volcanic Explosivity Index),Global Volcanism Program, Smithsonian National Museum of Natural History Archive.org link accessed 21 August 2014
  3. ↑ 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.
  4. ↑ Miles, M. G.; Grainger, R. G.; Highwood, E. J. (2004). "Volcanic Aerosols: The significance of volcanic eruption strength and frequency for climate" (PDF). Quarterly Journal of the Royal Meteorological Society 130 (602): 2361–2376. doi:10.1256/qj.30.60.

External links