Volcanic Explosivity Index.html



VEI and ejecta volume correlation

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.

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 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 8.¹

List of eruptions

See also

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

Footnotes

References

External links

• VEI glossary entry^{dead link} 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^{dead link}, a 2004 article from the Bulletin of Volcanology
• List of Large Holocene Eruptions (VEI > 4) from the Smithsonian Global Volcanism Program