Volcanic Explosivity Index
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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.
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[edit] Classification
| 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
[edit] List of eruptions
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]
[edit] See also
[edit] Footnotes
- ^ 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.
[edit] References
- 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.
[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
