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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 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 (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. Each interval on the scale represents a ten-fold 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 Footnotes 5 References 6 External links

VEI	Classification	Description	Plume	Ejecta volume	Frequency	Example	Occurrences †
0	Hawaiian	non-explosive	< 100 m	> 1000 m³	daily	Mauna Loa	-
1	Hawaiian/Strombolian	gentle	100-1000 m	> 10,000 m³	daily	Stromboli	-
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	Nevado del Ruiz (1985)	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)	4
8	Plinian/Ultra-Plinian	mega-colossal	> 25 km	> 1,000 km³	≥ 10,000 yrs	Toba (73,000 BP)	-

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

VEI	Name	Year
0	Mauna Loa	1984
	Piton de la Fournaise	2004
1	Kilauea	1983 - present
	Nyiragongo	2002
	Wells Gray-Clearwater Volcanic Field	1500?
2	Mount Hood	1865-1866
	Kilauea	1924
	Nazko Cone	7200 BP
	Tristan da Cunha	1961
	Whakaari/White Island	2001
	Mount Usu	2000-2001
3	Mount Vesuvius	1913-1944
	Surtsey	1963-1967
	Eldfell	1973
	Nevado del Ruiz	1985
	Mount Etna	2002-2003
4	Mount Pelée	1902
	Parícutin	1943-1952
	Hekla	1947
	Galunggung	1982
	Mount Spurr	1992
5	Mount Vesuvius (Pompeii eruption)	79
	Mount Agung	1963
	Mount St. Helens (1980 eruption)	1980
	El Chichón	1982
	Mount Hudson	1991
6	Mount Etna	8000 BP?
	Mount Vesuvius (Avellino eruption)	1660 BC ± 43 years
	Santorini (Minoan eruption)	1620s BC or 1520s BC
	Ilopango	450 ± 30 years
	Baekdu Mountain (Tianchi eruption)	1000
	Kuwae	1452 or 1453
	Huaynaputina	1600
	Laki	1783
	Krakatoa	1883
	Novarupta (1912 eruption)	1912
	Mount Meager	2350 BP
	Mount Pinatubo	1991
7	Yellowstone (Mesa Falls eruption)	1,300,000 BP
	Long Valley Caldera	760,000 BP
	Kurile	6440 BC ± 25 years
	Crater Lake Oregon (Mount Mazama eruption)	4860 BC
	Kikai (Akahoya eruption)	4350 BC
	Taupo (Hatepe eruption)	177, 181 or 186
	Mount Tambora	1815
	Bennett Lake Caldera	50 million years BP
8	La Garita Caldera	27 million years BP
	Yellowstone (Huckleberry Ridge eruption)	2,200,000 BP
	Yellowstone (Lava Creek eruption)	640,000 BP
	Toba	73,000 BP
	Taupo (Oruanui eruption)	26,500 BP

Note that there have not been any Holocene (within the last 10,000 years) eruptions with a VEI of 8. Lake Taupo's Oruanui eruption is probably the most recent, occurring 26,500 years ago. There is a new theory that the Minoan eruption of Santorini may have been twice as large as originally thought, placing it behind Taupo's Hatepe eruption and Mount Tambora as the third largest eruption in recorded history.^[1]

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

1. ^ McCoy, F. W. and Dunn, S., 2002, Modelling the Climatic Effects fo the LBA Eruption of Thera: New Calculations of Tephra Volumes May Suggest a Significantly Larger Eruption than Previously Reported [abst.]; Proceedings of the Chapman Conference on Volcanism and the Earth’s Atmosphere, Am. Geophysical Union, Santorini, Greece: 21-22.

• Christopher G. Newhall and Steve Self (Journal of Geophysical Research, v. 87, p. 1231–1238, 1982)
• Ben G. Mason; David M. Pyle, and Clive Oppenheimer (2004). "The size and frequency of the largest explosive eruptions on Earth" (PDF). Bulletin of Volcanology 66 (8): 735-748. DOI:10.1007/s00445-004-0355-9. Retrieved on 2006-07-14. 

• 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