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( Mid-Atlantic Ridge)
The Mid-Atlantic Ridge (MAR) is a mid-ocean ridge, a divergent tectonic plate boundary located along the floor of the Atlantic Ocean. 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 MAR 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. A ridge under the Atlantic Ocean was first inferred by Matthew Fontaine Maury in 1850. The ridge was discovered during the expedition of the 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.[1] The existence of such a ridge was confirmed by sonar in 1925.[2] 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,[3] with its central valley being seismologically active and the epicentre of many earthquakes.[4][5] 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. [6] The discovery of this world-wide ridge system led to the theory of seafloor spreading and general acceptance of Wegener's theory of continental drift. 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 dissected 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.
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