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{{Short description|Predictive qualitative scale for explosiveness of volcanic eruptions}}
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[[File:VEIfigure en.svg|thumb|270px|VEI and ejecta volume correlation]]

The '''volcanic explosivity index''' ('''VEI''') is a scale used to measure the size of explosive volcanic eruptions. It was devised by [[Christopher G. Newhall]] of the [[United States Geological Survey]] and [[Stephen Self]] in 1982.

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 eruptions in history given a magnitude of 8. A value of 0 is given for non-explosive eruptions, defined as less than {{convert|10000|m3|cuft|abbr=on}} of [[tephra]] ejected; and 8 representing a [[supervolcanic eruption]] that can eject {{val|1.0|e=12|u=m3}} (240 cubic miles) of tephra and have a cloud column height of over {{convert|20|km|ft|abbr=on}}. The scale is logarithmic, with each interval on the scale representing a tenfold increase in observed ejecta criteria, with the exception of between VEI-0, VEI-1 and VEI-2.<ref>
{{cite journal
 |first1=Christopher G. |last1=Newhall
 |first2=Stephen |last2=Self
 |year=1982
 |title=The Volcanic Explosivity Index (VEI): An Estimate of Explosive Magnitude for Historical Volcanism
 |url=http://www.agu.org/books/hg/v002/HG002p0143/HG002p0143.pdf
 |journal=[[Journal of Geophysical Research]]
 |volume=87 |issue=C2 |pages=1231–1238
 |bibcode=1982JGR....87.1231N
 |doi=10.1029/JC087iC02p01231
 |archive-url=https://web.archive.org/web/20131213194307/http://www.agu.org/books/hg/v002/HG002p0143/HG002p0143.pdf
 |archive-date=December 13, 2013
}}</ref>

==Classification==
With indices running from 0 to 8, the VEI associated with an eruption is dependent on how much volcanic material is thrown out, to what height, and how long the eruption lasts. The scale is logarithmic from VEI-2 and up; an increase of 1 index indicates an eruption that is 10 times as powerful. As such, 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 one hundred, from {{convert|10000|to|1000000|m3|cuft|abbr=on}}, while the factor is ten between all higher indices. In the following table, the frequency of each VEI indicates the approximate frequency of new eruptions of that VEI or higher.
<!-- Please note that this is not a database of eruptions and only a small number of examples should be listed here, fitting on one line on PC. Examples used should be eruptions that are significantly noteworthy, more recent examples where appropriate, and not using the same volcano in more than one category. Eruptions must also have a confirmed VEI from the Global Volcanism Program, except for the pre-Holocene VEI 7/8 examples.-->

{| class="wikitable" 
! rowspan="2" | VEI
! rowspan="2" | Ejecta<br> volume<br>(bulk)
! style="width: 350px;"| Classification
! style="width: 100px;"| Description
! style="width: 100px;"| Plume
! style="width: 150px;"| Periodicity
! style="width: 100px;"| Tropospheric<br>injection
! style="width: 100px;"| Stratospheric<br>injection<ref>
{{cite web
 |title=Volcanic Explosivity Index (VEI)
 |url=http://www.volcano.si.edu/world/eruptioncriteria.cfm#VEI
 |work=Global Volcanism Program
 |publisher=[[Smithsonian Institution|Smithsonian National Museum of Natural History]]
 |access-date=August 21, 2014
 |archive-url=https://web.archive.org/web/20111110173623/http://www.volcano.si.edu/world/eruptioncriteria.cfm
 |archive-date=November 10, 2011
}}</ref>
|-
! colspan="7" style="font-size:90%; color:#888;" | Examples
|-
! rowspan="2" style="background-color: white;" | 0
| rowspan="2" | <&nbsp;10<sup>4</sup> m<sup>3</sup> || [[Hawaiian eruption|Hawaiian]] || Effusive || < 100 m || constant || negligible || none
|-
| colspan="7" style="font-size:90%; color:#888; max-width:1px; background:white;" | [[Kīlauea]], [[Mawson Peak]] (current), [[Fagradalsfjall]] (2021-2023), [[Mauna Loa]] ([[1975 eruption of Mauna Loa|1975]], [[1984 eruption of Mauna Loa|1984]], [[2022 eruption of Mauna Loa|2022]]), [[Piton de la Fournaise]] (current)
|-
! rowspan="2" style="background-color: #FFC;" | [[:Category:VEI-1 volcanoes|<span style="color: black;">1</span>]]
| rowspan="2" | >&nbsp;10<sup>4</sup> m<sup>3</sup> || Hawaiian / [[Strombolian eruption|Strombolian]] || Gentle || {{nowrap|100 m – 1 km}} || daily || minor || none
|-
| colspan="7" style="font-size:90%; color:#888; background:white;" | [[Mount Yake|Yakedake]] (1995), [[Dieng Volcanic Complex]] (1964, 1979, 2017), [[Havre Seamount]] ([[2012 Kermadec Islands eruption|2012]]), [[2023–2025 Sundhnúkur eruptions|Sundhnúkur]] (2023-2024)
|-
! rowspan="2" style="background-color: #FF3;" | [[:Category:VEI-2 volcanoes|<span style="color: black;">2</span>]]
| rowspan="2" | >&nbsp;10<sup>6</sup> m<sup>3</sup> || Strombolian / [[Vulcanian eruption|Vulcanian]] || Explosive || 1–5&nbsp;km || 2 weeks || moderate || none
|-
| colspan="7" style="font-size:90%; color:#888; max-width:1px; background:white;" | [[Mount Etna]], [[Stromboli]] (since 1934), [[Mount Unzen|Unzen]] ([[1792 Unzen landslide and tsunami|1792]]), [[Ritter Island]] ([[1888 Ritter Island eruption and tsunami|1888]]), [[Whakaari / White Island|White Island]] ([[2019 Whakaari / White Island eruption|2019]]), [[Mount Marapi|Marapi]] ([[2023 eruption of Mount Marapi|2023]])
|-
! rowspan="2" style="background-color: #FC0;" | [[:Category:VEI-3 volcanoes|<span style="color: black;">3</span>]]
| rowspan="2" | >&nbsp;10<sup>7</sup> m<sup>3</sup> || Strombolian / Vulcanian / [[Peléan eruption|Peléan]] / Sub-Plinian || Severe || 3–15&nbsp;km || 3 months || substantial || possible
|-
| colspan="7" style="font-size:90%; color:#888; max-width:1px; background:white;" | [[Surtsey]] (1963-1967), [[Nevado del Ruiz]] ([[Armero tragedy|1985]]), [[Mount Redoubt|Redoubt]] ([[KLM Flight 867|1989-1990]]), [[Mount Ontake|Ontake]] ([[2014 Mount Ontake eruption|2014]]), [[Kanlaon]] ([[2024 Kanlaon eruption|2024]])
|-
! rowspan="2" style="background-color: #F90;" | [[:Category:VEI-4 volcanoes|<span style="color: black;">4</span>]]
| rowspan="2" | >&nbsp;0.1&nbsp;km<sup>3</sup> || Peléan / [[Plinian eruption|Plinian]] / Sub-Plinian|| Catastrophic || > 10&nbsp;km || 18 months || substantial || definite
|-
| colspan="7" style="font-size:90%; color:#888; max-width:1px; background:white;" | [[Mount Bandai|Bandai]] ([[1888 eruption of Mount Bandai|1888]]), [[Mount Pelée|Pelée]] ([[1902 eruption of Mount Pelée|1902]]), [[Mount Lamington|Lamington]] ([[1951 eruption of Mount Lamington|1951]]), [[Eyjafjallajökull]] ([[2010 eruptions of Eyjafjallajökull|2010]]), [[Mount Merapi|Merapi]] ([[2010 eruptions of Mount Merapi|2010]]), [[Semeru]] ([[2021 Semeru eruption|2021]])
|-
! rowspan="2" style="background-color: #F60;" | [[:Category:VEI-5 volcanoes|<span style="color: black;">5</span>]]
| rowspan="2" | >&nbsp;1&nbsp;km<sup>3</sup> || Peléan / Plinian || Cataclysmic || > 20&nbsp;km || 12 years || substantial || significant
|-
| colspan="7" style="font-size:90%; color:#888; max-width:1px; background:white;" | [[Mount Vesuvius|Vesuvius]] ([[Eruption of Mount Vesuvius in 79 AD|79]]), [[Mount Fuji|Fuji]] ([[Hōei eruption|1707]]), [[Mount Tarawera|Tarawera]] ([[1886 eruption of Mount Tarawera|1886]]), [[Mount St. Helens|St. Helens]] ([[1980 eruption of Mount St. Helens|1980]]), [[Puyehue-Cordón Caulle|Puyehue]] ([[2011–2012 Puyehue-Cordón Caulle eruption|2011]]), [[Hunga Tonga–Hunga Haʻapai]] ([[2022 Hunga Tonga–Hunga Haʻapai eruption and tsunami|2022]])
|-
! rowspan="2" style="background-color: #F00;" | [[:Category:VEI-6 volcanoes|<span style="color: white;">6</span>]]
| rowspan="2" | >&nbsp;10&nbsp;km<sup>3</sup> || Plinian / [[Ultra-Plinian]]|| Colossal || > 30&nbsp;km || 50–100 years || substantial || substantial
|-
| colspan="7" style="font-size:90%; color:#888; max-width:1px; background:white;" | [[Lake Ilopango]] ([[Tierra Blanca Joven eruption|450]]), [[Paektu Mountain|Paektu]] ([[946 eruption of Paektu Mountain|946]]), [[Huaynaputina]] ([[Huaynaputina#1600 eruption|1600]]), [[Krakatoa]] ([[1883 eruption of Krakatoa|1883]]), [[Santa María (volcano)|Santa Maria]] ([[1902 eruption of Santa María|1902]]), [[Santorini]] ([[Minoan eruption|1600 BC]]),<ref>https://volcano.oregonstate.edu/santorini#:~:text=Santorini%20is%20complex%20of%20overlapping,an%20eruption%2021%2C000%20year%20ago</ref> [[Novarupta]] ([[Novarupta#Eruption of 1912|1912]]),  [[Mount Pinatubo|Pinatubo]] ([[1991 eruption of Mount Pinatubo|1991]])
|-
! rowspan="2" style="background-color: #900;" | [[:Category:VEI-7 volcanoes|<span style="color: white;">7</span>]]
| rowspan="2" | >&nbsp;100&nbsp;km<sup>3</sup> || Ultra-Plinian || Super-colossal || > 40&nbsp;km || 500–1,000 years || substantial || substantial
|-
| colspan="7" style="font-size:90%; color:#888; max-width:1px; background:white;" | [[Long Valley Caldera|Long Valley]] ([[Bishop Tuff|760 kyr]]), [[Phlegraean Fields|Campi Flegrei]] ([[Campanian Ignimbrite eruption|37 kyr]]), Kuril Lake (6400 BC) , [[Mount Mazama|Mazama]] ([[Mazama Ash|5700 BC]]), [[Kikai Caldera|Kikai]] ([[Akahoya eruption|4300 BC]]), Cerro Blanco (2300 BC) , Taupo (232) , [[Lake Segara Anak|Samalas]] ([[1257 Samalas eruption|1257]]), [[Mount Tambora|Tambora]] ([[1815 eruption of Mount Tambora|1815]]) 
|-
! rowspan="2" style="background-color: black;" | [[:Category:VEI-8 volcanoes|<span style="color: white;">8</span>]]
| rowspan="2" | >&nbsp;1,000&nbsp;km<sup>3</sup> || Ultra-Plinian || Mega-colossal || > 50&nbsp;km || > 50,000 years<ref name="Dosseto">{{cite book | title=Timescales of Magmatic Processes: From Core to Atmosphere | publisher=Wiley-Blackwell | date=2011 |last1= Dosseto |first1= A. |editor-last1= Turner |editor-first1= S. P. |editor-last2= Van-Orman |editor-first2= J. A. |isbn= 978-1-4443-3260-5}}</ref><ref name="Rothery2010">{{citation | title=Volcanoes, Earthquakes and Tsunamis | publisher=Teach Yourself | date=2010 | last= Rothery |first= David A.}}</ref> || vast || vast
|-
| colspan="7" style="font-size:90%; color:#888; max-width:1px; background:white;" | [[Wah Wah Springs Caldera|Wah Wah Springs]] (30 Mya), [[La Garita Caldera|La Garita]] ([[Fish Canyon Tuff|26.3 Mya]]), [[Yellowstone Caldera|Yellowstone]] ([[Huckleberry Ridge Tuff|2.1 Mya]], [[Lava Creek Tuff|640 kyr]]), [[Lake Toba|Toba]] ([[Youngest Toba eruption|74 kyr]]), [[Taupō Volcano|Taupō]] ([[Oruanui eruption|26.5 kyr]])
|}

[[List of largest volcanic eruptions|About 40 eruptions]] of VEI-8 magnitude within the last 132 million years ([[megaannum|Mya]]) have been identified, of which 30 occurred in the past 36 million years. Considering the estimated frequency is on the order of once in 50,000 years,<ref name="Dosseto"/> there are likely many such eruptions in the last 132 Mya that are not yet known. Based on incomplete statistics, other authors assume that at least 60 VEI-8 eruptions have been identified.<ref name="Mason2004"/><ref>{{Cite journal|url= https://eprints.qut.edu.au/40259/1/c40259.pdf|title=The largest volcanic eruptions on Earth |last=Bryan |first=S.E. |date=2010 |journal=Earth-Science Reviews |volume=102 |issue=3–4 |pages=207–229 |doi=10.1016/j.earscirev.2010.07.001 |bibcode=2010ESRv..102..207B }}</ref> The most recent is [[Lake Taupō]]'s [[Oruanui eruption]], more than 27,000 years ago, which means that there have not been any [[Holocene]] eruptions with a VEI of 8.<ref name="Mason2004">
{{cite journal
 |last1= Mason |first1= Ben G.
 |last2= Pyle |first2= David M.
 |last3= Oppenheimer |first3= 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
 |bibcode = 2004BVol...66..735M
 |doi=10.1007/s00445-004-0355-9
|s2cid= 129680497
 }}</ref>

There have been at least [[List of large volcanic eruptions|10 eruptions of VEI-7]] in the last 11,700 years. There are also 58 Plinian eruptions, and 13 caldera-forming eruptions, of large, but unknown magnitudes. By 2010, the [[Global Volcanism Program]] of the [[Smithsonian Institution]] had cataloged the assignment of a VEI for 7,742 volcanic eruptions that occurred during the [[Holocene]] (the last 11,700 years) which account for about 75% of the total known eruptions during the Holocene. Of these 7,742 eruptions, about 49% have a VEI of 2 or lower, and 90% have a VEI of 3 or lower.<ref>
{{cite book
 |last1=Siebert |first1=L.
 |last2=Simkin |first2=T.
 |last3=Kimberly |first3=P.
 |date=2010
 |title=Volcanoes of the World
 |edition=3rd |pages=28–38
 |publisher=[[University of California Press]]
 |isbn=978-0-520-26877-7
}}</ref>

==Limitations==
Under the VEI, [[Volcanic ash|ash]], [[lava]], [[volcanic bomb|lava bombs]], and [[ignimbrite]] are all treated alike. [[Density]] and [[Vesicular texture|vesicularity]] (gas bubbling) of the volcanic products in question is not taken into account. In contrast, the DRE ([[dense-rock equivalent]]) is sometimes calculated to give the actual amount of [[magma]] erupted. Another weakness of the VEI is that it does not take into account the power output of an eruption, which makes the VEI extremely difficult to determine with prehistoric or unobserved eruptions.

Although VEI is quite suitable for classifying the explosive magnitude of eruptions, the index is not as significant as [[sulfur dioxide]] emissions in quantifying their atmospheric and climatic impact.<ref name=JRMS>{{cite journal  |last1=Miles |first1=M. G. |last2=Grainger |first2=R. G. |last3=Highwood |first3=E. J. |year=2004 |title=Volcanic Aerosols: The significance of volcanic eruption strength and frequency for climate | url=http://eodg.atm.ox.ac.uk/eodg/papers/2004Miles1.pdf |journal=[[Quarterly Journal of the Royal Meteorological Society]] |volume=130 |issue=602 |pages=2361–2376 |doi=10.1256/qj.03.60 |bibcode=2004QJRMS.130.2361M|s2cid=53005926 }}</ref>

==Lists of notable eruptions==
{{Volcanic Eruption Map}}
* [[Timeline of volcanism on Earth]] (mostly VEI-6, within 2 kya)
* [[List of volcanic eruptions 1500–2000]]
* [[List of volcanic eruptions in the 21st century]]
* [[List of volcanic eruptions by death toll]]
* [[List of large Holocene volcanic eruptions]] (VEI-5–7)
* [[List of large volcanic eruptions]] (VEI-5–8, within 450+ Mya)
* [[List of largest volcanic eruptions]] (VEI-7–8, mostly within 500 Mya)

==See also==
* {{annotated link |Supervolcano}} 
* {{annotated link |Decade Volcanoes}}
* {{annotated link |Dispersal index}}
* [[Lists of volcanoes]]
* [[List of natural disasters by death toll]]
{{clear}}

==References==
{{reflist}}

==External links==
* [https://volcanoes.usgs.gov/vsc/glossary/vei.html VEI glossary entry] from a [[United States Geological Survey|USGS]] website
* [https://web.archive.org/web/20070312094637/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]]''
* [https://doi.org/10.1007%2Fs00445-004-0355-9 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] {{Webarchive|url=https://web.archive.org/web/20120117212357/http://volcano.si.edu/world/largeeruptions.cfm |date=2012-01-17 }}

{{List of volcanoes}}

[[Category:Volcanology]]
[[Category:Hazard scales]]
[[Category:1982 introductions]]