The Mid-Atlantic Ridge (MAR) is a mid-ocean ridge, a divergent tectonic plate boundary located along the floor of the Atlantic Ocean, and part of the 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.
A ridge under the Atlantic Ocean was first inferred by Matthew Fontaine Maury in 1850. The ridge was discovered during the expedition of HMS Challenger in 1872. 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. The existence of such a ridge was confirmed by sonar in 1925 and was found to extend around the Cape of Good Hope into the Indian Ocean by the German Meteor expedition.
In the 1950s, mapping of the Earth’s ocean floors by Bruce Heezen, Maurice Ewing, Marie Tharp and others revealed the Mid-Atlantic Ridge to have a strange bathymetry of valleys and ridges, with its central valley being seismologically active and the epicentre of many earthquakes. Ewing and Heezen discovered the ridge to be part of a 40,000-km-long essentially continuous system of mid-ocean ridges on the floors of all the Earth’s oceans. The discovery of this worldwide ridge system led to the theory of seafloor spreading and general acceptance of 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 ), in the Arctic Ocean
- Iceland (Hvannadalshnúkur in the Vatnajökull, 2109.6 m (at ), through which the ridge runs
- Azores (Ponta do Pico or Pico Alto, on Pico Island, 2351 m, (at )
- Bermuda (Town Hill, on Main Island, 76 m (at ) (Bermuda was formed on the ridge, but is now considerably west of it)
- Saint Peter and Paul Rocks (Southwest Rock, 22.5 m, at )
Southern Hemisphere (South Atlantic Ridge):
- Ascension Island (The Peak, Green Mountain, 859 m, at )
- Tristan da Cunha (Queen Mary's Peak, 2062 m, at )
- Gough Island (Edinburgh Peak, 909 m, at )
- Bouvet Island (Olavtoppen, 780 m, at )
- 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 three-armed grabens 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 aulacogens, 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.
- Evans, Rachel. "Plumbing Depths to Reach New Heights: Marie Tharp Explains Marine Geological Maps." The Library of Congress Information Bulletin. November 2002.
- ^ USGS (5 May 1999). "Understanding plate motions". http://pubs.usgs.gov/gip/dynamic/understanding.html. Retrieved 13 March 2011.
- ^ Hsü, Kenneth J. (1992) Challenger at Sea, Princeton, Princeton University Press, page 57
- ^ Redfern, R.; 2001: Origins, the Evolution of Continents, Oceans and Life, University of Oklahoma Press, ISBN 1841881929, p. 26
- ^ Alexander Hellemans and Brian Bunch, 1989, Timeline of Science, Sidgwick and Jackson, London
- ^ Stein, Glenn, A Victory in Peace: The German Atlantic Expedition 1925-27, June 2007
- ^ Ewing, W.M.; Dorman, H.J.; Ericson, J.N. & Heezen, B.C.; 1953: Exploration of the northwest Atlantic mid-ocean canyon, Bulletin of the Geological Society of America 64, p. 865-868
- ^ Heezen, B. C. & Tharp, M.; 1954: Physiographic diagram of the western North Atlantic, Bulletin of the Geological Society of America 65, p. 1261
- ^ 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
- ^ Edgar W. Spencer, 1977, Introduction to the Structure of the Earth, 2nd edition, McGraw-Hill, Tokyo
- ^ "The Mediterranean Was a Desert" by Kenneth J. Hsü, illustration 13.
Mid-ocean ridges Present FormerPhoenix · Kula–Farallon · Pacific–Farallon · Pacific–Kula
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Look at other dictionaries:
Mid-Atlantic Ridge — /mid at lan tik, mid at lan / a north south suboceanic ridge in the Atlantic Ocean from Iceland to Antarctica on whose crest are several groups of islands; shown by plate tectonics to be the axis along which North America has split away from… … Universalium
Mid-Atlantic Ridge — Mid′ Atlan′tic Ridge′ n. oce a north south suboceanic ridge in the Atlantic Ocean from Iceland to Antarctica on whose crest are several groups of islands … From formal English to slang
Mid-Atlantic Ridge — noun a very long narrow elevation on the ocean floor that runs all the way from Iceland in the North Atlantic to Bouvet Island in the South Atlantic • Instance Hypernyms: ↑ridge • Part Holonyms: ↑Atlantic, ↑Atlantic Ocean … Useful english dictionary
Mid-Atlantic Ridge Ecosystem Project — More Information Name: MAR ECO Established: 2002 Headquarters: Norwegian Institute of Marine Research Website Click here … Wikipedia
Mid-Indian Ridge — ▪ ridge, Indian Ocean submarine ridge of the Indian Ocean that is a direct continuance of the Mid Atlantic Ridge; both are segments of the worldwide midoceanic ridge system. Entering the Indian Ocean from the South Atlantic, the Mid Indian… … Universalium
Mid-ocean ridge — Oceanic ridge, including a black smoker A mid ocean ridge is a general term for an underwater mountain system that consists of various mountain ranges (chains), typically having a valley known as a rift running along its spine, formed by plate… … Wikipedia
mid-ocean ridge — /mid oh sheuhn/ any of several seismically active submarine mountain ranges that extend through the Atlantic, Indian, and South Pacific oceans: each is hypothesized to be the locus of seafloor spreading. [1960 65] * * * mid ocean ridge noun… … Useful english dictionary
mid-oceanic ridge — [mid ō′shənmid ō΄shē an′ik] n. the continuous, double ridged chain of mountains on the ocean floor, extending through the middle of the Atlantic Ocean and into the Indian and Pacific oceans: also called mid ocean ridge [mid ō′shən] * * * … Universalium
mid-oceanic ridge — [mid ō′shənmid ō΄shē an′ik] n. the continuous, double ridged chain of mountains on the ocean floor, extending through the middle of the Atlantic Ocean and into the Indian and Pacific oceans: also called mid ocean ridge [mid ō′shən] … English World dictionary
mid-ocean ridge — /mid oh sheuhn/ any of several seismically active submarine mountain ranges that extend through the Atlantic, Indian, and South Pacific oceans: each is hypothesized to be the locus of seafloor spreading. [1960 65] * * * … Universalium