Editing Mid-Atlantic Ridge

{{Short description|Atlantic Ocean tectonic plate boundary}}
[[Image:Atlantic bathymetry.jpg|thumb|upright=1.35|A [[bathymetric map]] of the Mid-Atlantic Ridge (shown in light blue in the middle of the Atlantic Ocean)]]

The '''Mid-Atlantic Ridge''' is a [[mid-ocean ridge]] (a [[Divergent boundary|divergent]] or constructive [[Plate tectonics|plate boundary]]) located along the floor of the [[Atlantic Ocean]], and part of the [[List of longest mountain chains on Earth|longest mountain range in the world]]. In the North Atlantic, the ridge separates the [[North American plate|North American]] from the [[Eurasian plate]] and the [[African plate]], north and south of the [[Azores triple junction]]. In the South Atlantic, it separates the [[African plate|African]] and [[South American plate|South American]] plates. The ridge extends from a junction with the [[Gakkel Ridge]] (Mid-Arctic Ridge) northeast of [[Greenland]] southward to the [[Bouvet triple junction]] in the South Atlantic. Although the Mid-Atlantic Ridge is mostly an underwater feature, portions of it have enough elevation to extend above sea level, for example in [[Iceland]]. The ridge has an average spreading rate of about {{convert|2.5|cm|in|0}} per year.<ref name="USGS_understanding">{{cite web|url=http://pubs.usgs.gov/gip/dynamic/understanding.html|title=Understanding plate motions|publisher=United States Geological Survey|date=5 May 1999|access-date=13 March 2011}}</ref>

==Discovery==
[[Image:Pangea animation 03.gif|thumb|200px|[[Pangaea|Pangaea's]] separation (animated)]]
A ridge under the northern Atlantic Ocean was first inferred by [[Matthew Fontaine Maury]] in 1853, based on soundings by the [[USS Dolphin (1836)|USS ''Dolphin'']]. The existence of the ridge and its extension into the South Atlantic was confirmed during the [[Challenger expedition|expedition of HMS ''Challenger'']] in 1872.<ref name="Searle_2013">{{Cite book |last=Searle |first=R. |title=Mid-Ocean Ridges |publisher=[[Cambridge University Press]] |year=2013 |url = https://books.google.com/books?id=VdSaAAAAQBAJ&q=%22Tizard%22+1876+map&pg=PA4|isbn=9781107017528 |pages=3–4}}</ref><ref>{{cite book|last1=Hsü|first1=Kenneth J.|title=Challenger at Sea: A Ship That Revolutionized Earth Science|date=1992|publisher=[[Princeton University Press]]|isbn=978-0-691-08735-1|page=57|url=https://books.google.com/books?id=ZlQABAAAQBAJ&pg=PA57}}</ref> A team of scientists on board, led by [[Charles Wyville Thomson]], discovered a large rise in the middle of the Atlantic while investigating the future location for a [[transatlantic telegraph cable]].<ref>Redfern, R.; 2001: ''Origins, the Evolution of Continents, Oceans and Life'', [[University of Oklahoma]] Press, {{ISBN|1-84188-192-9}}, p. 26</ref> The existence of such a ridge was confirmed by sonar in 1925<ref>Alexander Hellemans and Brian Bunch, 1989, ''Timeline of Science'', Sidgwick and Jackson, London</ref> and was found to extend around [[Cape Agulhas]] into the [[Indian Ocean]] by the [[German Meteor expedition]].<ref name=Stein>{{Cite web |url=http://ipy.arcticportal.org/ipy-blogs/item/831-a-victory-in-peace-the-german-atlantic-expedition-1925-27 |title=Stein, Glenn, ''A Victory in Peace: The German Atlantic Expedition 1925–27,'' June 2007 |access-date=2010-06-23 |archive-url=https://web.archive.org/web/20160309101405/http://ipy.arcticportal.org/ipy-blogs/item/831-a-victory-in-peace-the-german-atlantic-expedition-1925-27 |archive-date=2016-03-09 |url-status=dead }}</ref>

In the 1950s, [[seafloor mapping|mapping of the Earth's ocean floors]] by [[Marie Tharp]], [[Bruce C. Heezen|Bruce Heezen]], [[Maurice Ewing]], and others revealed that the Mid-Atlantic Ridge had a strange [[bathymetry]] of valleys and ridges,<ref>{{cite journal | last1 = Ewing | first1 = W.M. | author-link = Maurice Ewing | author-link4 = Bruce Heezen | last2 = Dorman | first2 = H.J. | last3 = Ericson | first3 = J.N. | last4 = Heezen | first4 = B.C. | year = 1953 | title = Exploration of the northwest Atlantic mid-ocean canyon | journal = [[Bulletin of the Geological Society of America]] | volume = 64 | issue = 7| pages = 865–868 | doi=10.1130/0016-7606(1953)64[865:eotnam]2.0.co;2}}</ref> with its central valley being [[seismology|seismologically]] active and the [[epicenter]] of many [[earthquake]]s.<ref>{{cite journal | last1 = Heezen | first1 = B. C. | author-link2 = Marie Tharp | last2 = Tharp | first2 = M. | year = 1954 | title = Physiographic diagram of the western North Atlantic | journal = [[Bulletin of the Geological Society of America]] | volume = 65 | page = 1261 }}</ref><ref>{{cite journal | last1 = Hill | first1 = M.N. | last2 = Laughton | first2 = A.S. | year = 1954 | title =  Seismic Observations in the Eastern Atlantic, 1952 | journal = Proceedings of the Royal Society of London A: Mathematical and Physical Sciences | volume = 222 | issue = 1150| pages = 348–356 | doi=10.1098/rspa.1954.0078| bibcode = 1954RSPSA.222..348H | s2cid = 140604584 }}</ref> Ewing, Heezen and Tharp discovered that the ridge is part of a {{convert|40,000|km|mi|abbr=on|adj=on}} long essentially continuous system of [[mid-ocean ridge]]s on the floors of all the Earth's oceans.<ref>{{cite book |first=Edgar W. |last=Spencer |year=1977 |title=Introduction to the Structure of the Earth |edition=2nd |publisher=McGraw-Hill |location=Tokyo |isbn=978-0-07-085751-3 |url=https://books.google.com/books?id=uAi0AAAAIAAJ }}</ref> The discovery of this worldwide ridge system led to the theory of [[seafloor spreading]] and general acceptance of [[Alfred Wegener]]'s theory of [[continental drift]] and expansion in the modified form of [[plate tectonics]]. The ridge is a feature whose contribution to the breakup of the [[supercontinent]] of [[Pangaea]], in the period from about 200 to 160 million years ago, is considered in the modelling of such breakup in modern tectonic theory, where subduction and mantle plumes mechanisms are hypothesised to be primary, although historically this was contentious.<ref>{{cite journal|last=Keppie|first=D.F.|year=2015|title=How the closure of paleo-Tethys and Tethys oceans controlled the early breakup of Pangaea|journal=Geology|volume=43|issue=4|pages=335–338|doi=10.1144/SP424.8|doi-access=free}}</ref><ref>{{cite journal|last1=Dang|first1=Z.|last2=Zhang|first2=N.|last3=Li|first3=Z.X.|last4=Yan|first4=P.|year=2023|title=Pangaea's breakup: the roles of mantle plumes, orogens and subduction retreat|journal=Geological Society, London, Special Publications| volume=542|issue=1|at=345|doi=10.1144/SP542-2022-345|bibcode=2023GSLSP.542..345D}}</ref>

==Notable features==
{{Multiple image
 | image1 = Iceland Mid-Atlantic Ridge map.svg | width1 = 150
 | image2 = Iceland mid atlantic ridge.JPG | width2 = 205
 | footer = In Iceland the Mid-Atlantic Ridge passes across the [[Þingvellir]] National Park, a popular destination for tourists
}}
The Mid-Atlantic Ridge includes a deep [[rift valley]] that runs along the axis of the ridge for nearly its entire length. This rift marks the actual boundary between adjacent tectonic plates, where [[magma]] from the [[Mantle (geology)|mantle]] reaches the seafloor, erupting as [[lava]] and producing new [[Oceanic crust|crustal]] material for the plates.

Near the [[equator]], the Mid-Atlantic Ridge is divided into the North Atlantic Ridge and the South Atlantic Ridge by the [[Romanche Trench]], a narrow submarine [[Oceanic trench|trench]] with a maximum depth of {{convert|7758|m|ft|abbr=on}}, one of the deepest locations of the Atlantic Ocean. This trench, however, is not regarded as the boundary between the North and South American plates, nor the Eurasian and African plates.

==Islands==
{{maplink|frame=yes|frame-align=right|frame-width=150|frame-height=340|frame-long=-23.0|frame-lat=45.0|zoom=1|raw={{Wikipedia:Map data/Fracture zone}}|text=Approximate surface projection on Atlantic Ocean of Mid-Atlantic Ridge (purple). Associated fracture zones (orange) are also shown. 
Click to expand map to obtain interactive details.<ref name=FZmaplink>General citations for named fracture zones are at page [[Wikipedia:Map data/Fracture zone]] and specific citations are in interactive detail.</ref>}}
The islands on or near the Mid-Atlantic Ridge, from north to south, with their respective highest peaks and location, are:

'''Northern Hemisphere (North Atlantic Ridge)''':
#[[Jan Mayen]] ([[Beerenberg]], {{convert|2277|m|ft}} (at {{coord|71|06|N|08|12|W}}), in the [[Arctic Ocean]]
#[[Iceland]] ([[Hvannadalshnúkur]] at [[Vatnajökull]], {{convert|2109.6|m|ft}} (at {{coord|64|01|N|16|41|W}}), through which the ridge runs
#[[Azores]] ([[Ponta do Pico]] or Pico Alto, on [[Pico Island]], {{convert|2351|m|ft}}, (at {{coord|38|28|0|N|28|24|0|W}})
#[[Saint Peter and Paul Rocks]] (Southwest Rock, {{convert|22.5|m|ft}}, at {{coord|00|55|08|N|29|20|35|W}})
'''Southern Hemisphere (South Atlantic Ridge)''':
#[[Ascension Island]] (The Peak, Green Mountain, {{convert|859|m|ft}}, at {{coord|07|59|S|14|25|W}})
#[[Saint Helena]] ([[Diana's Peak]], {{convert|818|m|ft}} at {{coord|15|57|S|5|41|W}})
#[[Tristan da Cunha]] ([[Queen Mary's Peak]], {{convert|2062|m|ft}}, at {{coord|37|05|S|12|17|W}})
#[[Gough Island]] ([[Gough Island|Edinburgh Peak]], {{convert|909|m|ft}}, at {{coord|40|20|S|10|00|W}})
#[[Bouvet Island]] ([[Olavtoppen]], {{convert|780|m|ft}}, at {{coord|54|24|S|03|21|E}})

===Iceland===
The submarine section of the Mid-Atlantic Ridge close to southwest Iceland is known as the '''Reykjanes Ridge'''. The Mid-Atlantic Ridge runs through Iceland where the ridge is also known as the ''Neovolcanic Zone''. In northern Iceland the [[Tjörnes fracture zone]] connects Iceland to the [[Kolbeinsey Ridge]].

==Geology==
{{for-multi|a general explanation of mid-oceanic ridges|Mid-ocean ridge|and|Seafloor spreading}}
[[File:Expl2286 - Flickr - NOAA Photo Library.jpg|thumb|Basaltic rocks of the Mid-Atlantic Ridge observed by the ''Hercules'' [[Remotely operated underwater vehicle|ROV]] during the 2005 [[Lost City Hydrothermal Field|Lost City]] Expedition]]

The ridge sits atop a geologic feature known as the '''Mid-Atlantic Rise''', which is a progressive bulge that runs the length of the Atlantic Ocean, with the ridge resting on the highest point of this linear bulge. This bulge is thought to be caused by upward convective forces in the [[asthenosphere]] pushing the [[oceanic crust]] and [[lithosphere]]. This divergent boundary first formed in the [[Triassic]] period, when a series of [[triple junction|three-armed]] [[graben]]s coalesced on the supercontinent [[Pangaea]] to form the ridge. Usually, only two arms of any given three-armed graben become part of a divergent plate boundary. The failed arms are called ''[[aulacogen]]s'', and the aulacogens of the Mid-Atlantic Ridge eventually became many of the large river valleys seen along the [[Americas]] and [[Africa]] (including the [[Mississippi River]], [[Amazon River]] and [[Niger River]]). The [[Fundy Basin]] on the Atlantic coast of North America between [[New Brunswick]] and [[Nova Scotia]] in [[Canada]] is evidence of the ancestral Mid-Atlantic Ridge.<ref>{{Cite journal
 | last1 = Burke
 | first1 = K.
 | last2 = Dewey
 | first2 = J. F.
 | authorlink2 = John Frederick Dewey
 | title = Plume-generated triple junctions: key indicators in applying plate tectonics to old rocks
 | year = 1973
 | journal = The Journal of Geology
 | volume = 81
 | issue = 4
 | pages = 406–433
 | doi = 10.1086/627882
 | jstor = 30070631
 | bibcode = 1973JG.....81..406B
 | s2cid = 53392107
 | url = http://es.ucsc.edu/~rcoe/eart206/Burke&Dewey_Aulacogens-%20TJs_JGeol73.pdf
 | access-date = 2022-02-26
 | archive-date = 2016-10-23
 | archive-url = https://web.archive.org/web/20161023202901/http://es.ucsc.edu/~rcoe/eart206/Burke%26Dewey_Aulacogens-%20TJs_JGeol73.pdf
 | url-status = dead
 }}<!-- {{Harvnb|Burke|Dewey|1973}}  --></ref><ref>{{Cite journal
 | last = Burke | first = K.
 | title = Development of graben associated with the initial ruptures of the Atlantic Ocean
 | year = 1976 | journal = Tectonophysics | volume = 36 | issue = 1–3 | pages = 93–112
 | doi=10.1016/0040-1951(76)90009-3| bibcode = 1976Tectp..36...93B
 | citeseerx = 10.1.1.473.8997
 }}<!-- {{Harvnb|Burke|1976}} --></ref>

==See also==
{{Portal|Volcanoes|Geography}}
* [[Atlantis Massif]]
* [[Canadian Arctic Rift System]]
* [[Central Atlantic Magmatic Province]]
* [[Charlie–Gibbs fracture zone]]
* [[East Pacific Rise]]
* [[Fifteen-Twenty fracture zone]]
* [[Project FAMOUS]]
* [[Researcher Ridge]]

==References==
{{reflist}}

==Bibliography==
* Evans, Rachel. "[https://www.loc.gov/loc/lcib/0211/tharp.html Plumbing Depths to Reach New Heights: Marie Tharp Explains Marine Geological Maps.]" ''The Library of Congress Information Bulletin.'' November 2002.

==External links==
{{Commons category|Mid-Atlantic Ridge}}
*[http://www.mar-eco.no/ MAR-ECO, a Census of Marine Life project on life along the Mid-Atlantic Ridge] {{Webarchive|url=https://web.archive.org/web/20150402011542/http://www.mar-eco.no/ |date=2015-04-02 }}

{{mid-ocean ridges}}
{{Tectonic plates}}

{{Authority control}}

[[Category:Mid-Atlantic Ridge| ]]
[[Category:Mesozoic rifts and grabens]]
[[Category:Cenozoic rifts and grabens]]