Editing Shield volcano (section)

==Distribution==
{{main|List of shield volcanoes}}
Shield volcanoes are found worldwide. They can form over hotspots (points where magma from below the surface wells up), such as the [[Hawaiian–Emperor seamount chain]] and the [[Galápagos Islands]], or over more conventional rift zones, such as the [[Volcanism of Iceland|Icelandic shields]] and the shield volcanoes of East Africa. Although shield volcanoes are not usually associated with [[subduction]], they can occur over subduction zones. Many examples are found in California and Oregon, including Prospect Peak in [[Lassen Volcanic National Park]], as well as [[Pelican Butte]] and [[Belknap Crater]] in Oregon. Many shield volcanoes are found in [[Oceanic basin|ocean basins]], such as [[Kīlauea]] in Hawaii, although they can be found inland as well&mdash;East Africa being one example of this.<ref name="bk-2009">{{cite book|title=The changing Earth : exploring geology and evolution|year=2006|publisher=Brooks/Cole|location=Belmont, CA|isbn=978-0-495-55480-6|url=https://books.google.com/books?id=jFPMa4MxwJkC&q=shield+volcanoes+africa&pg=PA115|author1=James S. Monroe |author2=Reed Wicander |edition=5th|access-date=February 22, 2011|page=115}}</ref>

=== Hawaiian–Emperor seamount chain ===
The largest and most prominent shield volcano chain in the world is the Hawaiian–Emperor seamount chain, a chain of hotspot volcanoes in the Pacific Ocean. The volcanoes follow a distinct [[Evolution of Hawaiian volcanoes|evolutionary pattern]] of growth and death.<ref>{{cite web|title=Evolution of Hawaiian Volcanoes|url=http://hvo.wr.usgs.gov/volcanowatch/1995/95_09_08.html|publisher=Hawaiian Volcano Observatory - United States Geological Survey|access-date=28 February 2011|date=8 September 1995}}</ref> The chain contains at least 43 major volcanoes, and [[Meiji Seamount]] at its terminus near the [[Kuril–Kamchatka Trench]] is 85&nbsp;million years old.<ref>{{cite journal|doi=10.1093/petrology/44.1.113|last=Regelous|first=M.|author2=Hofmann, A.W.|author3=Abouchami, W.|author4=Galer, S.J.G.|year=2003|title=Geochemistry of Lavas from the Emperor Seamounts, and the Geochemical Evolution of Hawaiian Magmatism from 85 to 42 Ma|journal=[[Journal of Petrology]]|volume=44|issue=1|pages=113–140|url=http://www.gzn.uni-erlangen.de/fileadmin/data/kruste/mitarbeiter/Marcel/JPET2003.pdf|access-date=13 February 2011|url-status=dead|archive-url=https://web.archive.org/web/20110719101930/http://www.gzn.uni-erlangen.de/fileadmin/data/kruste/mitarbeiter/Marcel/JPET2003.pdf|archive-date=19 July 2011|bibcode=2003JPet...44..113R|doi-access=free}}</ref> 

The youngest part of the chain is Hawaii, where the volcanoes are characterized by frequent rift eruptions, their large size (thousands of km<sup>3</sup> in volume), and their rough, decentralized shape. Rift zones are a prominent feature on these volcanoes and account for their seemingly random volcanic structure.<ref name=hvw-shield /> They are fueled by the movement of the [[Pacific Plate]] over the [[Hawaii hotspot]] and form a long chain of volcanoes, [[atoll]]s, and [[seamount]]s {{convert|2600|km|mi|0|abbr=on}} long with a total volume of over {{convert|750000|km3|cumi|0|abbr=on}}.<ref name="lt">{{cite web|last=Watson|first=Jim|title=The long trail of the Hawaiian hotspot|url=http://pubs.usgs.gov/gip/dynamic/Hawaiian.html|publisher=United States Geological Survey|access-date=13 February 2011|date=5 May 1999}}</ref>

The chain includes Mauna Loa, a shield volcano which stands {{convert|4170|m|ft|abbr=on}} above sea level and reaches a further {{convert|13|km|0|abbr=on}} below the waterline and into the crust, approximately {{convert|80000|km3|cumi|abbr=on}} of rock.<ref name=vhp-shield /> [[Kīlauea]], another Hawaiian shield volcano, is one of the most active volcanoes on Earth, with its most recent eruption occurring in 2021.<ref name="usgs-shield"/>

=== Galápagos Islands ===
The [[Galápagos Islands]] are an isolated set of volcanoes, consisting of shield volcanoes and lava plateaus, about {{convert|1100|km|mi|abbr=on}} west of Ecuador. They are driven by the [[Galápagos hotspot]], and are between approximately 4.2&nbsp;million and 700,000 years of age.<ref name=uoo-galapagos/> The largest island, [[Isabela Island (Galápagos)|Isabela]], consists of six coalesced shield volcanoes, each delineated by a large summit caldera. [[Española Island|Española]], the oldest island, and [[Fernandina Island|Fernandina]], the youngest, are also shield volcanoes, as are most of the other islands in the chain.<ref name="hvw">{{cite web|title=How Volcanoes Work: Galapagos Shield Volcanoes|url=http://www.geology.sdsu.edu/how_volcanoes_work/Thumblinks/Galapagos_page.html|publisher=San Diego State University|access-date=22 February 2011|archive-date=3 December 2010|archive-url=https://web.archive.org/web/20101203205121/http://www.geology.sdsu.edu/how_volcanoes_work/Thumblinks/Galapagos_page.html|url-status=dead}}</ref><ref>{{cite web |url=http://www.galapagosonline.com/Galapagos_Natural_History/Geology/Volcanoes.html |archive-url=https://web.archive.org/web/20010723104558/http://galapagosonline.com/Galapagos_Natural_History/Geology/Volcanoes.html |url-status=dead |archive-date=23 July 2001 |title=Volcanoes |publisher=Galapagos Online Tours and Cruises |access-date=22 February 2011 }}</ref><ref name="vsa">{{cite web|title=Volcanoes of South America: Galápagos Islands|url=http://www.volcano.si.edu/world/region.cfm?rnum=1503|work=[[Global Volcanism Program]]|publisher=Smithsonian National Museum of Natural History|access-date=22 February 2011}}</ref> The Galápagos Islands are perched on a large lava plateau known as the Galápagos Platform. This platform creates a shallow water depth of {{convert|360|to|900|m|ft|0|abbr=on}} at the base of the islands, which stretch over a {{convert|174|mi|km|0|abbr=on}} diameter.<ref name=uog /> Since [[Charles Darwin]]'s visit to the islands in 1835 during the [[Second voyage of HMS Beagle|second voyage of HMS ''Beagle'']], there have been over 60 recorded eruptions in the islands, from six different shield volcanoes.<ref name="hvw" /><ref name="vsa" /> Of the 21 emergent volcanoes, 13 are considered active.<ref name=uoo-galapagos>{{cite web|title=Volcanic Galapagos: Formation of an Oceanic Archipelago|url=http://darkwing.uoregon.edu/~drt/Research/Volcanic%20Galapagos/presentation.view@_id=9889959127044&_page=0&_part=0&.html|publisher=University of Oregon|access-date=23 February 2011|author1=Bill White  |author2=Bree Burdick |name-list-style=amp }}</ref>

[[Cerro Azul (Ecuador volcano)|Cerro Azul]] is a shield volcano on the southwestern part of Isabela Island and is one of the most active in the Galapagos, with the last eruption between May and June 2008.  The Geophysics Institute at the [[National Polytechnic School (Ecuador)|National Polytechnic School]] in [[Quito]] houses an international team of [[seismology|seismologists]] and [[volcanologist]]s<ref>[http://www.igepn.edu.ec/  Institute for Geophysics at National Polytechnic School   ]</ref> whose responsibility is to monitor Ecuador's numerous active volcanoes in the Andean Volcanic Belt and the Galapagos Islands.  [[La Cumbre (Galápagos Islands)|La Cumbre]] is an active shield volcano on Fernandina Island that has been erupting since April 11, 2009.<ref>{{cite web|title=Galapagos volcano erupts, could threaten wildlife|url=https://news.yahoo.com/s/ap/20090412/ap_on_re_la_am_ca/lt_ecuador_galapagos_volcano|archive-url=https://web.archive.org/web/20090415162111/http://news.yahoo.com/s/ap/20090412/ap_on_re_la_am_ca/lt_ecuador_galapagos_volcano|archive-date=2009-04-15|date=October 22, 2015}}</ref>

The Galápagos islands are geologically young for such a big chain, and the pattern of their rift zones follows one of two trends, one north-northwest, and one east–west. The composition of the lavas of the Galápagos shields are strikingly similar to those of the Hawaiian volcanoes. Curiously, they do not form the same volcanic "line" associated with most hotspots. They are not alone in this regard; the [[Cobb–Eickelberg Seamount chain]] in the North Pacific is another example of such a delineated chain. In addition, there is no clear pattern of age between the volcanoes, suggesting a complicated, irregular pattern of creation. How the islands were formed remains a geological mystery, although several theories have been proposed.<ref name=usgs-galapagos>{{cite journal|last=Bailey|first=K.|title=Potassium-Argon Ages from the Galapagos Islands|journal=[[Science (journal)|Science]]|date=30 April 1976|volume=192|issue=4238|pages=465–467|doi=10.1126/science.192.4238.465|bibcode = 1976Sci...192..465B|pmid=17731085|s2cid=11848528}}</ref>

=== Iceland ===
[[File:Skjaldbreidur Herbst 2004.jpg|thumb|right|[[Skjaldbreiður]] is a shield volcano in [[Iceland]], whose name means ''broad shield'' in Icelandic.]]

Located over the [[Mid-Atlantic Ridge]], a [[Divergent boundary|divergent]] [[plate tectonics|tectonic plate]] boundary in the middle of the Atlantic Ocean, Iceland is the site of about 130 volcanoes of various types.<ref name=worldbook /> Icelandic shield volcanoes are generally of [[Holocene]] age, between 5,000 and 10,000 years old. The volcanoes are also very narrow in distribution, occurring in two bands in the West and North Volcanic Zones. Like Hawaiian volcanoes, their formation initially begins with several eruptive centers before centralizing and concentrating at a single point. The main shield then forms, burying the smaller ones formed by the early eruptions with its lava.<ref name=uog/>

Icelandic shields are mostly small (~{{convert|15|km3|cumi|0|abbr=on}}), symmetrical (although this can be affected by surface topography), and characterized by eruptions from summit calderas.<ref name=uog>{{cite web|title=Holocene shield volcanoes in Iceland|url=http://geoleoedocs.sub.uni-goettingen.de:8080/dspace/bitstream/gledocs-108/1/Andrews%2BGudmundsson.pdf|publisher=University of Göttingen|access-date=21 February 2011|author1=Ruth Andrews|author2=Agust Gudmundsson|name-list-style=amp|year=2006|url-status=dead|archive-url=https://web.archive.org/web/20070611035239/http://geoleoedocs.sub.uni-goettingen.de:8080/dspace/bitstream/gledocs-108/1/Andrews%2BGudmundsson.pdf|archive-date=11 June 2007}}</ref> They are composed of either [[Tholeiitic magma series|tholeiitic]] [[olivine]] or [[Picrite basalt|picritic basalt]]. The tholeiitic shields tend to be wider and shallower than the picritic shields.<ref name=1996-iceland>{{cite journal|last=Rossi|first=M. J.|title=Morphology and mechanism of eruption of postglacial shield volcanoes in Iceland|journal=[[Bulletin of Volcanology]]|year=1996|volume=57|issue=7|pages=530–540|doi=10.1007/BF00304437|bibcode=1996BVol...57..530R|s2cid=129027679}}</ref> They do not follow the pattern of caldera growth and destruction that other shield volcanoes do; caldera may form, but they generally do not disappear.<ref name=hvw-shield /><ref name="uog" />

=== Turkey ===
[[Bingöl Mountains]] are one of the shield volcanoes in [[Turkey]].
=== East Africa ===

In East Africa, volcanic activity is generated by the development of the [[East African Rift]] and from nearby hotspots. Some volcanoes interact with both. Shield volcanoes are found near the rift and off the coast of Africa, although stratovolcanoes are more common. Although sparsely studied, the fact that all of its volcanoes are of Holocene age reflects how young the volcanic center is. One interesting characteristic of East African volcanism is a penchant for the formation of [[lava lake]]s; these semi-permanent lava bodies, extremely rare elsewhere, form in about 9% of African eruptions.<ref name=usgs-africa>{{cite web|title=Africa Volcanoes and Volcanics|url=http://vulcan.wr.usgs.gov/Volcanoes/Africa/description_africa_volcanics.html|publisher=United States Geological Survey|access-date=28 February 2011|author=Lyn Topinka|date=2 October 2003}}</ref>

The most active shield volcano in Africa is [[Nyamuragira]]. Eruptions at the shield volcano are generally centered within the large summit caldera or on the numerous fissures and cinder cones on the volcano's flanks. Lava flows from the most recent century extend down the flanks more than {{convert|30|km|mi|0|abbr=on}} from the summit, reaching as far as [[Lake Kivu]]. [[Erta Ale]] in Ethiopia is another active shield volcano and one of the few places in the world with a permanent lava lake, which has been active since at least 1967, and possibly since 1906.<ref name=usgs-africa/> Other volcanic centers include [[Menengai]], a massive shield caldera,<ref>{{cite web|title=Menengai|url=http://www.volcano.si.edu/world/volcano.cfm?vnum=0202-06=|work=[[Global Volcanism Program]]|publisher=Smithsonian National Museum of Natural History|access-date=28 February 2011}}</ref> and [[Mount Marsabit]] in Kenya.
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=== Extraterrestrial shield volcanoes ===
{{See also|Category:Lists of extraterrestrial mountains}}
[[File:Olympus Mons and Hawaii to scale.png|thumb|left|Scaled image showing [[Olympus Mons]], top, and the [[Hawaiian Islands|Hawaiian island chain]], bottom. [[Volcanology of Mars|Martian volcanoes]] are far larger than those found on Earth.]]

Shield volcanoes are not limited to Earth; they have been found on [[Mars]], [[Venus]], and [[Jupiter|Jupiter's]] moon, [[Io (moon)|Io]].<ref name="dk">{{cite book|title=Space Encyclopedia|year=1999|publisher=Dorling Kindersley|isbn=978-0-7894-4708-1|author1=Heather Couper|author2=Nigel Henbest|name-list-style=amp|url-access=registration|url=https://archive.org/details/dkspaceencyclope00coup}}</ref>

The [[Volcanism on Mars|shield volcanoes of Mars]] are very similar to the shield volcanoes on Earth. On both planets, they have gently sloping flanks, collapse craters along their central structure, and are built of highly fluid lavas. Volcanic features on Mars were observed long before they were first studied in detail during the 1976–1979 [[Viking program|Viking mission]]. The principal difference between the volcanoes of Mars and those on Earth is in terms of size; Martian volcanoes range in size up to {{convert|14|mi|km|0|abbr=on}} high and {{convert|370|mi|0|abbr=on}} in diameter, far larger than the {{convert|6|mi|km|0|abbr=on}} high, {{convert|74|mi|km|0|abbr=on}} wide Hawaiian shields.<ref>{{cite web|url=http://pubs.usgs.gov/gip/volc/extraterrestrial.html|title=Extraterrestrial Volcanism|publisher=United States Geological Survey|date=February 5, 1997|author=Watson, John|access-date=February 13, 2011}}</ref><ref>{{cite journal|last1=Masursky|first1= H.|year=1973|last2=Masursky|first2=Harold|last3=Saunders|first3=R. S.|title=An Overview of Geological Results from Mariner 9 | journal = [[Journal of Geophysical Research]]|volume= 78|issue=20|pages=4009–4030|doi=10.1029/JB078i020p04031|bibcode=1973JGR....78.4031C}}</ref><ref>Carr, M.H., 2006, The Surface of Mars, Cambridge, 307 p.</ref> The highest of these, [[Olympus Mons]], is the tallest known mountain on any planet in the solar system.

[[Volcanism on Venus|Venus has over 150 shield volcanoes]] which are much flatter, with a larger surface area than those found on Earth, some having a diameter of more than {{convert|700|km|mi|abbr=on}}.<ref>{{cite web|url=http://volcano.oregonstate.edu/oldroot/volcanoes/planet_volcano/venus/large_shield.html|title=Large Shield Volcanoes|publisher=Oregon State University|access-date=April 14, 2011|archive-date=January 5, 2018|archive-url=https://web.archive.org/web/20180105225607/http://volcano.oregonstate.edu/oldroot/volcanoes/planet_volcano/venus/large_shield.html|url-status=dead}}</ref> Although the majority of these are long extinct it has been suggested, from observations by the [[Venus Express|Venus Express spacecraft]], that many may still be active.<ref>{{cite web|url=http://www.universetoday.com/62328/volcanoes-on-venus-may-still-be-active|date=8 April 2010|title=Volcanoes on Venus May Still Be Active|author=Nancy Atkinson|work=[[Universe Today]]|access-date=April 14, 2011}}</ref>
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