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 Hawaiokinai 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 convert|25|km|mi|abbr=on|lk=off. 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.

Classification

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

Note that 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."* Count of eruptions in the last 10,000 years 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.cite journal |last=Mason |first=Ben G. |authorlink= |coauthors=Pyle, David M.; Oppenheimer, Clive |year=2004 |month= |title=The size and frequency of the largest explosive eruptions on Earth |journal=Bulletin of Volcanology |volume=66 |issue=8 |pages=735–748 |doi=10.1007/s00445-004-0355-9 |url= |accessdate= |quote= ]

List of eruptions

ee also

*Supervolcano
*List of volcanoes
*List of deadliest natural disasters

Footnotes

References

*cite journal
first = Christopher G.
last = Newhall
coauthors = Self, Steve
year = 1982
title = The volcanic explosivity index (VEI): An estimate of explosive magnitude for historical volcanism
journal = Journal of Geophysical Research
volume = 87
issue = C2
pages = 1231–1238
url = http://www.agu.org/pubs/crossref/1982/JC087iC02p01231.shtml
doi = 10.1029/JC087iC02p01231
*cite journal
first = Ben G.
last = Mason
coauthors = Pyle, David M.; Oppenheimer, Clive
year = 2004
title = The size and frequency of the largest explosive eruptions on Earth
journal = Bulletin of Volcanology
volume = 66
issue = 8
pages = 735–748
doi = 10.1007/s00445-004-0355-9

External links

* [http://volcanoes.usgs.gov/Products/Pglossary/vei.html VEI glossary entry] from a USGS website
* [http://talk.workunlimited.co.uk/life/feature/story/0,13026,1294868,00.html How to measure the size of a volcanic eruption] , from "The Guardian"
* [http://springerlink.metapress.com/openurl.asp?genre=article&doi=10.1007/s00445-004-0355-9 The size and frequency of the largest explosive eruptions on Earth] , a 2004 article from the "Bulletin of Volcanology"
* [http://www.volcano.si.edu/world/largeeruptions.cfm List of Large Holocene Eruptions (VEI > 4) from the Smithsonian Global Volcanism Program]