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The Volcanic Explosivity Index (VEI) was devised by Chris Newhall of the U.S. Geological Survey and Steve Self at the University of Hawaiʻi 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 (less than 10⁴ cubic metres of tephra ejected) with 8 representing a mega-colossal explosive eruption that can eject 10¹² cubic metres of tephra and have a cloud column height of over 25 km (16 mi). Each interval on the scale represents a tenfold increase in observed eruption criteria.

Note that ash, volcanic bombs, and ignimbrite are all treated alike — this is due to taking into account the vesicularity (gas bubbling) of the volcanic products in question and the DRE (Dense-Rock Equivalent) is calculated to give the actual amount of magma erupted. One weakness of the VEI is that it does not take into account the magnitude of power output of an eruption. This, of course, is extremely difficult to detect with prehistoric or unobserved eruptions.

Contents 1 Classification 2 List of eruptions 3 See also 4 References 5 External links

[edit] Classification

Scientists indicate how powerful volcanic eruptions are using the VEI. The VEI stands for Volcanic Explosivity Index. It records how much volcanic material is thrown out, how high the eruption goes, and how long it lasts. The scale goes from 0 to 8. An increase of 1 indicates a 10 times more powerful eruption.

Note: 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 while the factor is 10 between all higher indices.

VEI	Classification	Description	Plume	Ejecta volume	Frequency	Example	Occurrences*
0	Hawaiian	non-explosive	< 100 m	< 10,000 m³	daily	Mauna Loa	many
1	Hawaiian/Strombolian	gentle	100-1000 m	> 10,000 m³	daily	Stromboli	many
2	Strombolian/Vulcanian	explosive	1-5 km	> 1,000,000 m³	weekly	Galeras (1993)	3477*
3	Vulcanian/Pelean	severe	3-15 km	> 10,000,000 m³	yearly	Koryaksky	868
4	Pelean/Plinian	cataclysmic	10-25 km	> 0.1 km³	≥ 10 yrs	Soufrière Hills (1995)	278
5	Plinian	paroxysmal	> 25 km	> 1 km³	≥ 50 yrs	St. Helens (1980)	84
6	Plinian/Ultra-Plinian	colossal	> 25 km	> 10 km³	≥ 100 yrs	Mount Pinatubo (1991)	39
7	Plinian/Ultra-Plinian	super-colossal	> 25 km	> 100 km³	≥ 1000 yrs	Tambora (1815)	5 (+2 suspected)
8	Ultra-Plinian	mega-colossal	> 25 km	> 1,000 km³	≥ 10,000 yrs	Toba (73,000 BP)	0

*Count of eruptions in the last 10,000 years are based on 1994 figures maintained by the Global Volcanism Program of the Smithsonian Institution.

A total of 47 eruptions of VEI–8 magnitude or above, ranging in age from Ordovician to Pleistocene, are identified, of which 42 eruptions are known from the past 36 million years. The most recent one is Lake Taupo's Oruanui eruption, occurring 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.^[1]

[edit] List of eruptions

VEI	Name	Year
0	Mauna Loa	1984
	Piton de la Fournaise	2004
	Hoodoo Mountain	7050 BC?
1	Kilauea	1983 - present
	Nyiragongo	2002
	Wells Gray-Clearwater volcanic field	1500?
2	Mount Hood	1865-1866
	Kilauea	1924
	Tristan da Cunha	1961
	Whakaari/White Island	2001
	Mount Usu	2000-2001
3	Mount Vesuvius	1913-1944
	Mount Edziza	950 AD ± 1000 years
	Surtsey	1963-1967
	Eldfell	1973
	Nevado del Ruiz	1985
	Mount Etna	2002-2003
	Mount Garibaldi	9,300 BP
	Nazko Cone	7,200 BP
4	Mount Pelée	1902
	Parícutin	1943-1952
	Hekla	1947
	Galunggung	1982
	Mount Spurr	1992
5	Hekla (Hekla 3 eruption)	1021 + 130/-100 BC
	Mount Vesuvius (Pompeian eruption)	79
	Mount Tarumae	1739
	Mount Agung	1963
	Mount St. Helens (1980 eruption)	1980
	Mount Meager	≈400 BC (2350 BP)
	El Chichón	1982
	Mount Hudson	1991
	Mount Tarawera	1886
6	Morne Diablotins	30,000 BP
	Laacher See	12,900 BP?
	Nevado de Toluca	10,500 BP
	Mount Okmok	8300 BP
	Mount Etna	8000 BP?
	Mount Veniaminof	1750 BC
	Mount Vesuvius (Avellino eruption)	1660 BC ± 43 years
	Thera (Minoan eruption)	1620s BC
	Mount Aniakchak	≈1645 BC
	Mount Okmok	2400 BP
	Mount Churchill (White River Ash)	≈750 (1200 BP)
	Ilopango	450 ± 30 years
	Laki	934
	Baekdu Mountain (Tianchi eruption)	969 ± 20 years
	Kuwae	1452 or 1453
	Huaynaputina	1600
	Laki	1783
	Krakatoa	1883
	Santa María	1902
	Novarupta	1912
	Mount Pinatubo	1991
7	Bennett Lake Volcanic Complex	50 Ma
	Valles (Lower Bandelier eruption)	1.47 Ma
	Yellowstone (Mesa Falls eruption)	1.3 Ma
	Valles (Upper Bandelier eruption)	1.15 Ma
	Long Valley Caldera (Bishop eruption)	759,000 BP
	Manijau	280,000 BP
	Atitlán (Los Chocoyos eruption)	84,000 BP
	Kurile (Golygin eruption)	41,000 BP
	Campi Flegrei	37,000 BP
	Aira Caldera	22,000 BP
	Kurile (Ilinsky eruption)	6440 BC ± 25 years
	Crater Lake, Oregon (Mount Mazama eruption)	5677 BC ± 150 years
	Kikai (Akahoya eruption)	≈5300 BC
	Taupo (Hatepe eruption)	186
	Mount Tambora	1815
8	La Garita Caldera	27 Ma
	Yellowstone (Huckleberry Ridge eruption)	2.2 Ma
	Galán	2.2 Ma
	Yellowstone (Lava Creek eruption)	640,000 BP
	Toba	73,000 BP
	Taupo (Oruanui eruption)	26,500 BP

[edit] See also

• Supervolcano
• List of volcanoes
• List of deadliest natural disasters

[edit] References

[edit] External links

• 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