Volcanic explosive index

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The volcanic explosivity index abbreviated VEI (from English Volcanic Explosivity Index ) is an indication of the strength of an explosive volcanic eruption in values from 0 to 8 on a logarithmic stepped scale. Measured variables are primarily the amount of volcanic loose material ( tephra ) expelled , as well as the height of the eruption column and qualitative descriptions. It was introduced in 1982 by the US geologists Christopher G. Newhall and Stephen Self .

The scale begins with level 0 and is logarithmic from level 2, so that the class limits of the next higher levels, measured by the volume of ejected pyroclastic material, correspond to a volcanic eruption ten times larger. Starting with a harmless volcanic event, it extends to a gigantic eruption with global effects of level 8. The scale is open at the top. Scientists point out that it is very difficult to accurately measure the strength of volcanic eruptions.

Volcanic explosive index

VEI 0 1 2 3 4th 5 6th 7th 8th
classification not explosive small moderate moderate to large big very large
Ejected tephra volume 1 ≤ 10 4 10 4 -10 6 10 6 -10 7 10 7 -10 8 10 8 -10 9 1-10 10-100 100-1000 ≥ 1000
m³ km³
Height of the eruption column [km] ≤ 0.1 0.1-1 1-5 3-15 10-25 ≥ 25
Number of events since the last glacial period 11,700 years ago 3,631 924 307 106 46 5 0
Well-known example
(year of outbreak) 		Kīlauea
(1977) 		Poas
(1991) 		Ruapehu
(1971) 		Nevado del Ruiz
(1985) 		Eyjafjallajökull
(2010) 		Mount St. Helens
(1980) 		Krakatau
(1883) 		Tambora
(1815) 		Taupo
(about 26,500 years ago)
1Tephra quantities of up to 10 4 m³ are classified as VEI level 0 , larger quantities of up to 10 6 m³ as 1 and only those above that are each graduated by a factor of 10 (the indices are not powers of ten ).

Examples from the history of the earth

Strength 8

The Toba eruption in Sumatra 74,000 years ago was the largest in the last two million years. It was also larger than the last major eruption of the Yellowstone volcano around 630,000 years ago. According to the controversially discussed Toba catastrophe theory , mankind at that time was decimated to a few thousand individuals and had to pass a so-called " genetic bottleneck ".

Strength 7

The eruption of the Phlegraean Fields 39,000 years ago with 250 km³ of tephra is an example of this level. The Minoan eruption of the volcano of Santorin about 3,600 years ago was smaller, but probably reached strength 7. More recent eruptions with a tephra ejection of 100 km³ or more occurred at Taupo in the 2nd or 3rd century, at Paektusan 969, at Samalas 1257 and at Tambora in 1815. The eruption of the Ilopango (around 430?), which did not quite reach magnitude 7, also had serious global consequences .

There have been no magnitude 8 eruptions in the past 10,000 years, but there have been at least seven magnitude 7 eruptions:

In addition, other eruptions are known from the last 2,000 years that were approximately 7:

  • Taupo (Hatepe eruption, around 130 to 230), around 100 km³ tephra
  • Ilopango (eruption dated to the 2nd to 6th century), about 84 km³ tephra
  • Paektusan around 946, with 96 (± 19) km³ tephra

Strength 6

A major eruption in Central Europe took place around 13,000 years ago at the Laacher volcano . The Laacher See represents the sagging caldera of the volcano. During the eruption, an area of ​​1300 km² was covered by a layer of lava up to 10 meters thick. The ash column rose up to 40 kilometers.

Strength 5

Strength 4

Magnitude

In the volcanological literature and the relevant databases, in addition to the VEI, the term magnitude (M), defined as:

 .

Using the ejected mass as a reference variable, differences in density of the various magma types and a different bubble content of the deposited material are balanced out, so that the eruptions are more comparable. The result now has one decimal place, but is predominantly in the order of magnitude of the previously assigned VEI. For example, results for 200,000  t ejected material a magnitude of .

Further classification methods of volcanic eruptions

  • Tsuya classes : Similar to the VEI, they are divided into classes I to IX.
  • Turbidity index : The turbidity index has a value of 1000 for the Krakatau eruption of 1883 and is used as a parameter to describe the volcanic disturbances in atmospheric layers, which can then influence the climate.
  • Volcano Population Index (CPI): The index indicates how many people live in a dangerous area within a certain radius of the eruption site during a volcanic eruption. VPI5 and VPI10 are often used, which stand for VPIs with a radius of 5 km and 10 km, respectively, the relevant areas for outbreaks with VEI 2 to 4.

See also

Remarks

  1. ↑ See e.g. B. http://www.geology.sdsu.edu/how_volcanoes_work/index.html NASA: Eruption Variability , How Volcanoes Work; Retrieved September 23, 2012.
  2. ↑ Number of known outbreaks of each strength in the Holocene , based on data from the Smithsonian Institute .
  3. ↑ Diagram of the USGS for the definition of the VEI The table in the article is essentially based on this diagram. Note the discontinuity in powers of ten of upper limits for the ejection quantity between VEI 0 and VEI 1, which unfortunately was not explained in the original source.
  4. ↑ Geological Society of America, October 27, 2017: Yellowstone Experienced Double Eruption , at [1] , accessed March 13, 2018.
  5. ↑ Brooks Mitchell: What Was the Biggest Volcanic Eruption in History? , at [2] , accessed June 10, 2018.
  6. ↑ Marc Szeglat: Super volcanoes and flood basalts , on [3] , accessed on March 13, 2018.
  7. ↑ See Sara Pratt: AAG: Eruption of El Salvador's Ilopango explains AD 536 cooling. from www.earthmagazine.org, February 2012, accessed June 11, 2018.
  8. ↑ C. Newhall, S. Self, A. Robock: Anticipating future Volcanic Explosivity Index (VEI) 7 eruptions and their chilling impacts. In: Geosphere. February 2018. Volume 14, No. 2, doi: 10.1130 / GES01513.1 , pp. 572–603.
  9. ^ W. Báez, E. Bustos, A. Chiodi, F. Reckziegel, M. Arnosio, S. Silva, G. Giordano, J. Viramonte, M. Sampietro-Vattuone, J. Peña-Monné: Eruptive style and flow dynamics of the pyroclastic density currents related to the Holocene Cerro Blanco eruption (Southern Puna plateau, Argentina). In: Journal of South American Earth Sciences. Volume 98, March 1, 2020, doi: 10.1016 / j.jsames.2019.102482 .
  10. ↑ Felix Riede: The eruption of the Laacher See volcano 12,920 years ago and prehistoric cultural change at the end of the Alleröd. A new hypothesis on the origin of the Bromme culture and Perstunia , on [4] , accessed June 11, 2018.
  11. ^ DM Pyle: "Sizes of volcanic eruptions." In Encyclopedia of Volcanoes. Academic Press, London 2000, ISBN 0-12-643140-X

literature

Web links