Mid-Atlantic Ridge

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Image:Mid-atlantic ridge map.png Image:Pangea animation 03.gif

The Mid-Atlantic Ridge is a mostly underwater mountain range of the Atlantic Ocean and Arctic Ocean that runs from 87°N (about 333 km South of the North Pole) to subantarctic Bouvet Island at 54°S. The highest peaks of this mountain range extend above the water mark, to form islands. The Mid-Atlantic Ridge forms part of the global mid-oceanic ridge system and, like all mid-oceanic ridges, is thought to result from a divergent boundary that separates tectonic plates: the North American Plate from the Eurasian Plate in the North Atlantic, and the South American Plate from the African Plate in the South Atlantic. These plates are still slowly moving apart, so the Atlantic is growing.

The ridge was discovered by Bruce Heezen and Marie Tharp in the 1950s. The discovery of this ridge led to the theory of seafloor spreading and general acceptance of Wegener's theory of continental drift.

1 Relation to other ridges and trenches
2 Islands on the Mid-Atlantic Ridge, from North to South
3 Geology
4 See also
5 References

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Relation to other ridges and trenches

At the South end near Bouvet Island, the Mid-Atlantic Ridge turns into the Atlantic-Indian-Ridge and continues further East through the Crozet Plateau to the Southwest Indian Ridge, while in the West it is followed by the Scotia Ridge.

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 7758 m, one of the deepest locations of the Atlantic Ocean.

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Islands on the Mid-Atlantic Ridge, from North to South

The islands are, from North to South, with their respective highest peaks, elevations in m, and location:

Northern Hemisphere (North Atlantic Ridge):

Jan Mayen (Beerenberg, 2277 m, at 71°06'N, 08°12'W), in the Arctic Ocean
Iceland (Hvannadalshnúkur in the Vatnajökull, 2119 m, at 64°01'N, 16°41'W)
Azores (Ponta do Pico or Pico Alto, on Pico Island, 2351 m, at 38°28'0"N, 28°24'0"W)
Saint Peter and Paul Rocks (Southwest Rock, 22.5 m, at 00°55'08"N, 29°20'35"W)

Southern Hemisphere (South Atlantic Ridge):

Ascension Island (The Peak, Green Mountain, 859 m, at 07°59'S, 14°25'W)
Tristan da Cunha (Queen Mary's Peak, 2062 m, at 37°05'S, 12°17'W)
Gough Island (Edinburgh Peak, 909 m, at 40°20'S, 10°00'W)
Bouvet Island (Olavtoppen, 780 m, at 54°24'S, 03°21'E)

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Geology

For a general explanation of mid-oceanic ridges, see mid-oceanic ridge and seafloor spreading

These mountain ranges are where tectonic plates move apart along a divergent boundary as magma rises from the Earth's mantle. Heat from the magma causes the crust on either side of the rifts to expand, forming the ridges.

The ridge actually sits on top of the mid-Atlantic rise which is a progressive bulge that also 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).

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