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[[Image:Mid-the mid atlantic ridge map.png|thumb|200px|Theis locationdumb ofand thei don Mid-Atlantictlike Ridge]]it
[[Image:Pangea animation 03.gif|thumb|200px|The ridge was central in the breakup of [[Pangaea]] that began some 180 million years ago.]]
[[Image:Iceland Mid-Atlantic Ridge Fig16.gif|thumb|200px|The Mid-Atlantic Ridge in [[Iceland]]]]
The '''Mid-Atlantic Ridge (MAR)''' is a [[mid-ocean ridge]], a [[Divergent boundary|divergent]] [[Plate tectonics|tectonic plate]] boundary located along the floor of the [[Atlantic Ocean]], and part of the [[List of mountain ranges#By length|longest mountain range in the world]]. It separates the [[Eurasian Plate]] and [[North American Plate]] in the North Atlantic, and the [[African Plate]] from the [[South American Plate]] in the South Atlantic. 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. The section of the ridge which includes the island of [[Iceland]] is also known as the '''Reykjanes Ridge'''. The average spreading rate for the ridge is about 2.5 cm per year.<ref name="USGS_understanding">{{cite web|url=http://pubs.usgs.gov/gip/dynamic/understanding.html|title=Understanding plate motions|last=USGS|date=5 May 1999|accessdate=13 March 2011}}</ref>
==Discovery==
A ridge under the Atlantic Ocean was first inferred by [[Matthew Fontaine Maury]] in 1850. The ridge was discovered during the [[Challenger expedition|expedition of HMS ''Challenger'']] in 1872.<ref>Hsü, Kenneth J. (1992) ''Challenger at Sea'', Princeton, Princeton University Press, page 57</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 1841881929, 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 the [[Cape of Good Hope]] into the [[Indian Ocean]] by the [[German Meteor expedition]].<ref name=Stein>[http://ipy.arcticportal.org/ipy-blogs/item/831-a-victory-in-peace-the-german-atlantic-expedition-1925-27 Stein, Glenn, ''A Victory in Peace: The German Atlantic Expedition 1925-27,'' June 2007]</ref>
In the 1950s, mapping of the Earth’s ocean floors by [[Bruce C. Heezen|Bruce Heezen]], [[Maurice Ewing]], [[Marie Tharp]] and others revealed the Mid-Atlantic Ridge to have a strange [[bathymetry]] of valleys and ridges,<ref>[[Maurice Ewing|Ewing, W.M.]]; Dorman, H.J.; Ericson, J.N. & [[Bruce Heezen|Heezen, B.C.]]; 1953: ''Exploration of the northwest Atlantic mid-ocean canyon'', Bulletin of the [[Geological Society of America]] '''64''', p. 865-868</ref> with its central valley being [[seismology|seismologically]] active and the [[epicentre]] of many [[earthquake]]s.<ref>Heezen, B. C. & [[Marie Tharp|Tharp, M.]]; 1954: ''Physiographic diagram of the western North Atlantic'', Bulletin of the [[Geological Society of America]] '''65''', p. 1261</ref><ref>Hill, M.N. & Laughton, A.S.; '''1954''': ''Seismic Observations in the Eastern Atlantic, 1952'', Proceedings of the [[Royal Society of London]], series A, mathematical & physical sciences '''222(1150)''', p. 348-356</ref> Ewing and Heezen discovered the ridge to be part of a 40,000-km-long essentially continuous system of [[mid-ocean ridge]]s on the floors of all the Earth’s oceans.<ref>Edgar W. Spencer, 1977, ''Introduction to the Structure of the Earth'', 2nd edition, McGraw-Hill, Tokyo</ref> The discovery of this worldwide ridge system led to the theory of [[seafloor spreading]] and general acceptance of [[Alfred Wegener|Wegener]]'s theory of [[continental drift]] and expansion as [[plate tectonics]].
==Notable features along the ridge==
The Mid-Atlantic Ridge includes a deep rift valley which runs along the axis of the ridge along nearly its entire length. This rift marks the actual boundary between adjacent tectonic plates, where [[magma]] from the mantle reaches the seafloor, erupting as [[lava]] and producing new 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 trench with a maximum depth of 7,758 m (25,453 ft), 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 on the Mid-Atlantic Ridge==
The islands, from north to south, with their respective highest peaks and location, are:
'''Northern Hemisphere (North Atlantic Ridge)''':
#[[Jan Mayen]] ([[Beerenberg]], 2277 m (at {{coord|71|06|N|08|12|W}}), in the [[Arctic Ocean]]
#[[Iceland]] ([[Hvannadalshnúkur]] in the [[Vatnajökull]], 2109.6 m (at {{coord|64|01|N|16|41|W}}), through which the ridge runs
#[[Azores]] ([[Ponta do Pico]] or Pico Alto, on [[Pico Island]], 2351 m, (at {{coord|38|28|0|N|28|24|0|W|}})
#[[Bermuda]] (Town Hill, on Main Island, 76 m (at {{coord|32|18|N|64|47|W}}) (Bermuda was formed on the ridge, but is now considerably west of it)
#[[Saint Peter and Paul Rocks]] (Southwest Rock, 22.5 m, at {{coord|00|55|08|N|29|20|35|W|}})
'''Southern Hemisphere (South Atlantic Ridge)''':
#[[Ascension Island]] (The Peak, Green Mountain, 859 m, at {{coord|07|59|S|14|25|W}})
#[[Tristan da Cunha]] ([[Queen Mary's Peak]], 2062 m, at {{coord|37|05|S|12|17|W}})
#[[Gough Island]] ([[Edinburgh Peak]], 909 m, at {{coord|40|20|S|10|00|W}})
#[[Bouvet Island]] ([[Olavtoppen]], 780 m, at {{coord|54|24|S|03|21|E}})
[[Image:Mid Atlantic Ridge.jpg|thumb|left|275px|A fissure running along the Mid Atlantic Ridge in [[Iceland]]]]
[[Image:Iceland mid atlantic ridge.JPG|thumb|left|Rock outcrop in [[Iceland]], a visible surface feature of the Mid-Atlantic Ridge, the Easternmost edge of the [[North American plate]]. It is a popular destination for tourists in Iceland.]]
==Geology==
:''For a general explanation of mid-oceanic ridges, see [[mid-oceanic ridge]] and [[seafloor spreading]]''
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 ridge is about 2,500 meters (8,200 ft) below sea level, while its flank is about 5,000 meters deeper.<ref>"The Mediterranean Was a Desert" by Kenneth J. Hsü, illustration 13.</ref>
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.
==See also==
*[[Atlantis Massif]]
==References==
;Bibliography
* Evans, Rachel. "[http://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.
;Notes
{{reflist}}
==External links==
*[http://www.mar-eco.no/ MAR-ECO, a Census of Marine Life project on life along the Mid-Atlantic Ridge]
{{mid-ocean ridges}}
[[Category:Environment of Iceland]]
[[Category:Plate tectonics]]
[[Category:Underwater ridges of the Atlantic Ocean]]
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