Editing Volcano (section)

==Volcanic activity== <!-- [[Dormant volcano]] redirects here -->
[[File:Pompeii - Casa del Centenario - MAN.jpg|thumb|left|upright|[[Fresco]] with [[Mount Vesuvius]] behind [[Bacchus]] and [[Agathodaemon]], as seen in [[Pompeii]]'s [[House of the Centenary]]]]

Volcanoes vary greatly in their level of activity, with individual volcanic systems having an ''eruption recurrence'' ranging from several times a year to once in tens of thousands of years.<ref>{{cite book|last1=Martí Molist|first1=Joan|title=Oxford Handbook Topics in Physical Sciences|chapter=Assessing Volcanic Hazard|date=September 6, 2017|volume=1|doi=10.1093/oxfordhb/9780190699420.013.32|isbn=978-0-19-069942-0}}</ref> Volcanoes are informally described as '''erupting''', '''active''', '''dormant''', or '''extinct''', but the definitions of these terms are not entirely uniform among volcanologists. The level of activity of most volcanoes falls upon a graduated spectrum, with much overlap between categories, and does not always fit neatly into only one of these three separate categories.<ref name=ade>{{cite web|last1=Pariona|first1=Amber|title=Difference Between an Active, Dormant, and Extinct Volcano|date=September 19, 2019|url=https://www.worldatlas.com/articles/when-is-a-volcano-considered-active-dormant-or-extinct.html|publisher=WorldAtlas.com|access-date=November 27, 2020}}</ref>

=== Erupting ===
The USGS defines a volcano as "erupting" whenever the ejection of magma from any point on the volcano is visible, including visible magma still contained within the walls of the summit crater.

===Active===
{{Main|Active volcano}}

While there is no international consensus among volcanologists on how to define an active volcano, the USGS defines a volcano as ''active'' whenever subterranean indicators, such as [[earthquake swarm]]s, ground inflation, or unusually high levels of carbon dioxide or sulfur dioxide are present.<ref>[https://www.usgs.gov/volcanoes/kilauea/recent-eruption Kilauea eruption confined to crater] {{Webarchive|url=https://web.archive.org/web/20220717144650/https://www.usgs.gov/volcanoes/kilauea/recent-eruption |date=July 17, 2022 }} usgs.gov. Updated July 24, 2022. Downloaded July 24, 2022.</ref><ref name="activity_levels">[https://www.wired.com/2015/08/tell-volcano-active-dormant-extinct/ How We Tell if a Volcano Is Active, Dormant, or Extinct] {{Webarchive|url=https://web.archive.org/web/20220725042124/https://www.wired.com/2015/08/tell-volcano-active-dormant-extinct/ |date=July 25, 2022 }} Wired. August 15, 2015. By Erik Klimetti. Downloaded July 24, 2022.</ref>

===Dormant and reactivated{{anchor|Dormant}}===
<!-- [[Dormant volcano]] redirects here -->
[[File:Narcondam island.jpg|thumb|[[Narcondam Island]], India, is classified as a dormant volcano by the [[Geological Survey of India]].]]
The USGS defines a dormant volcano as any volcano that is not showing any signs of unrest such as earthquake swarms, ground swelling, or excessive noxious gas emissions, but which shows signs that it could yet become active again.<ref name="activity_levels" /> Many dormant volcanoes have not erupted for thousands of years, but have still shown signs that they may be likely to erupt again in the future.<ref name="Nelson2016">{{cite web|url=http://www.tulane.edu/~sanelson/Natural_Disasters/volhaz&pred.htm|title=Volcanic Hazards & Prediction of Volcanic Eruptions|publisher=Tulane University|date=October 4, 2016|access-date=September 5, 2018|last=Nelson|first=Stephen A.}}</ref><ref name="VolcWorldDormant">{{cite web|url=http://volcano.oregonstate.edu/how-volcano-defined-being-active-dormant-or-extinct|title=How is a volcano defined as being active, dormant, or extinct?|work=Volcano World|publisher=Oregon State University|access-date=September 5, 2018|archive-date=January 12, 2013|archive-url=https://web.archive.org/web/20130112014631/http://volcano.oregonstate.edu/how-volcano-defined-being-active-dormant-or-extinct|url-status=dead}}</ref>

In an article justifying the re-classification of Alaska's [[Mount Edgecumbe (Alaska)|Mount Edgecumbe]] volcano from "dormant" to "active", volcanologists at the [[Alaska Volcano Observatory]] pointed out that the term "dormant" in reference to volcanoes has been deprecated over the past few decades and that "[t]he term "dormant volcano" is so little used and undefined in modern volcanology that the Encyclopedia of Volcanoes (2000) does not contain it in the glossaries or index",<ref>{{cite web|url=https://www.avo.alaska.edu/news.php?id=1576|title=Mount Edgecumbe volcanic field changes from 'dormant' to 'active' -- what does that mean?|author=<!--Not stated-->|date=May 9, 2022|publisher=Alaska Volcano Observatory|access-date=June 2, 2022}}</ref> however the USGS still widely employs the term.

Previously a volcano was often considered to be extinct if there were no written records of its activity. Such a generalization is inconsistent with observation and deeper study, as has occurred recently with the unexpected eruption of the [[Chaitén (volcano)|Chaitén volcano]] in 2008.<ref name=Castro2009>{{cite journal|last1=Castro|first1=J.|last2=Dingwell|first2=D.|title=Rapid ascent of rhyolitic magma at Chaitén volcano, Chile|journal=Nature|volume=461|pages=780–783|year=2009|issue=7265|doi=10.1038/nature08458|pmid=19812671|bibcode=2009Natur.461..780C|s2cid=4339493}}</ref> Modern volcanic activity monitoring techniques, and improvements in the modelling of the factors that produce eruptions, have helped the understanding of why volcanoes may remain dormant for a long time, and then become unexpectedly active again. The potential for eruptions, and their style, depend mainly upon the state of the magma storage system under the volcano, the eruption trigger mechanism and its timescale.<ref name="Cserép2023">{{cite journal|last1=Cserép|first1=B.|last2=Szemerédi|first2=M.|last3=Harangi|first3=S.|last4=Erdmann|first4=S.|last5=Bachmann|first5=O.|last6=Dunkl|first6=I.|last7=Seghedi|first7=I.|last8=Mészáros|first8=K.|last9=Kovács|first9=Z.|last10 =Virág| first10=A|last11=Ntaflos|first11=T.|title=Constraints on the pre-eruptive magma storage conditions and magma evolution of the 56–30 ka explosive volcanism of Ciomadul (East Carpathians, Romania)|journal=Contribribtions to Mineralogy and Petrology|volume=178|issue=96|year=2023|doi=10.1007/s00410-023-02075-z|bibcode=2023CoMP..178...96C|doi-access=free|hdl=20.500.11850/646219|hdl-access=free}}</ref>{{rp|95}} For example, the [[Yellowstone Caldera|Yellowstone]] volcano has a repose/recharge period of around 700,000 years, and [[Toba Lake|Toba]] of around 380,000 years.<ref name="chesner1991">{{cite journal|doi=10.1130/0091-7613(1991)019<0200:EHOESL>2.3.CO;2|url=http://www.geo.mtu.edu/~raman/papers/ChesnerGeology.pdf|last1=Chesner|first1=C.A.|last2=Rose|first2=J.A.|last3=Deino|first3=W.I.|last4=Drake|first4=R.|last5=Westgate|first5=A.|title=Eruptive History of Earth's Largest Quaternary caldera (Toba, Indonesia) Clarified|volume=19|pages=200–203|journal=Geology|date=March 1991|access-date=January 20, 2010|issue=3|bibcode=1991Geo....19..200C}}</ref> [[Vesuvius]] was described by Roman writers as having been covered with gardens and vineyards before its unexpected [[Eruption of Mount Vesuvius in 79|eruption of 79 CE]], which destroyed the towns of [[Herculaneum]] and [[Pompeii]].

Accordingly, it can sometimes be difficult to distinguish between an extinct volcano and a dormant (inactive) one. Long volcano dormancy is known to decrease awareness.<ref name="Cserép2023"/>{{rp|96}} [[Pinatubo]] was an inconspicuous volcano, unknown to most people in the surrounding areas, and initially not seismically monitored before its unanticipated and catastrophic eruption of 1991. Two other examples of volcanoes that were once thought to be extinct, before springing back into eruptive activity were the long-dormant [[Soufrière Hills]] volcano on the island of [[Montserrat]], thought to be extinct until activity resumed in 1995 (turning its capital [[Plymouth, Montserrat|Plymouth]] into a [[ghost town]]) and [[Fourpeaked Mountain]] in Alaska, which, before its September 2006 eruption, had not erupted since before 8000 BCE.

===Extinct===
<!-- [[Extinct volcano]] redirects here -->
[[File:Capulin 1980 tde00005.jpg|thumb|[[Capulin Volcano National Monument]] in New Mexico, US]]
Extinct volcanoes are those that scientists consider unlikely to erupt again because the volcano no longer has a magma supply. Examples of extinct volcanoes are many volcanoes on the [[Hawaiian–Emperor seamount chain]] in the Pacific Ocean (although some volcanoes at the eastern end of the chain are active), [[Hohentwiel]] in [[Germany]], [[Shiprock]] in [[New Mexico]], [[United States|U.S.]], [[Capulin Volcano National Monument|Capulin]] in New Mexico, U.S, [[Zuidwal volcano]] in the [[Netherlands]], and many volcanoes in [[Italy]] such as [[Monte Vulture]]. [[Edinburgh Castle]] in Scotland is located atop an extinct volcano, which forms [[Castle Rock (Edinburgh)|Castle Rock]]. Whether a volcano is truly extinct is often difficult to determine. Since "supervolcano" [[caldera]]s can have eruptive lifespans sometimes measured in millions of years, a caldera that has not produced an eruption in tens of thousands of years may be considered dormant instead of extinct. An individual volcano in a monogenetic volcanic field can be extinct, but that does not mean a completely new volcano might not erupt close by with little or no warning, as its field may have an active magma supply.

===Volcanic-alert level===
The three common popular classifications of volcanoes can be subjective and some volcanoes thought to have been extinct have erupted again. To help prevent people from falsely believing they are not at risk when living on or near a volcano, countries have adopted new classifications to describe the various levels and stages of volcanic activity.<ref>{{cite web|url=http://www.volcanolive.com/alerts.html|title=Volcanic Alert Levels of Various Countries|publisher=Volcanolive.com|access-date=August 22, 2011}}</ref> Some alert systems use different numbers or colours to designate the different stages. Other systems use colours and words. Some systems use a combination of both.