Volcanic Explosivity Index
From Biocrawler, the free encyclopedia.
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 and ranges from 0, for non-explosive eruptions (less than 104 cubic metres of tephra ejected), to 8, for mega-colossal explosive eruptions 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. Values higher than 8 can be determined if needed.
One weakness of the VEI is that it does not take into account of the density of erupted material; ash, volcanic bombs, and ignimbrite are all treated alike. In addition, the VEI does not take into account the magnitude of power output of an eruption.
| VEI | Classification | Description | Plume height | Volume ejected | How often | Example | Total historic eruptions as of 1994 |
|---|---|---|---|---|---|---|---|
| 0 | Hawaiian | non-explosive | < 100 m | > 1000 m³ | daily | Kilauea | - |
| 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, 1992 | 3477 |
| 3 | Vulcanian (Sub-Plinian) | severe | 3-15 km | > 10,000,000 m³ | yearly | Nevado del Ruiz, 1985 | 868 |
| 4 | Vulcanian (Sub-Plinian)/ Plinian | cataclysmic | 10-25 km | > 0.1 km³ | ≥ 10 yrs | Galunggung, 1982 | 278 |
| 5 | Plinian | paroxysmal | > 25 km | > 1 km³ | ≥ 100 yrs | St. Helens, 1980 | 84 |
| 6 | Plinian/ Ultra-Plinian (Krakatoan) | colossal | > 25 km | > 10 km³ | ≥ 100 yrs | Krakatau, 1883 | 39 |
| 7 | Ultra-Plinian (Krakatoan) | super-colossal | > 25 km | > 100 km³ | ≥ 1000 yrs | Tambora, 1815 | 4 |
| 8 | Ultra-Plinian (Krakatoan) | mega-colossal | > 25 km | > 1000 km³ | ≥ 10,000 yrs | Toba, 71,000 BP | 1 |
Count of historic eruptions based on 1994 figures maintained by the Global Volcanism Program of the Smithsonian Institution
List of eruptions and their VEI
- Nevado del Ruiz, 1985 (VEI 3)
- Mount St. Helens, 1980 eruption (VEI 5)
- El Chichon, 1982 (VEI 5)
- Laki, 1783 (VEI 6)
- Krakatoa, 1883 (VEI 6)
- Novarupta (Katmai), 1912 (VEI 6)
- Mount Pinatubo, 1991 (VEI 6)
- Santorini (Thera), 1640 BC (VEI 6-7)
- Taupo, 181 (VEI 6-7)
- Mount Tambora, 1815 (VEI 6-7)
- Long Valley Caldera, 760,000 BP (VEI 7)
- Yellowstone, 640,000 BP (VEI 8)
- Toba 73,000 BP (VEI 8)
See also
References and external links
- Christopher G. Newhall and Steve Self (Journal of Geophysical Research, v. 87, p. 1231–1238, 1982)
- VEI glossary entry (http://volcanoes.usgs.gov/Products/Pglossary/vei.html) from a USGS website
- How to measure the size of a volcanic eruption (http://talk.workunlimited.co.uk/life/feature/story/0,13026,1294868,00.html), from The Guardian
- The size and frequency of the largest explosive eruptions on Earth (http://springerlink.metapress.com/openurl.asp?genre=article&id=doi:10.1007/s00445-004-0355-9), a 2004 article from the Bulletin of Volcanologyit:VEI
