Mid-Atlantic Ridge

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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 moving apart, so the Atlantic is growing at the ridge, at a rate of about 2.5 centimeters per year in an east–west direction.

Contents 1 Discovery 2 Proximity to other ridges and trenches 3 Islands on the Mid-Atlantic Ridge 4 Geology 5 See also 6 References

[edit] Discovery

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.

[edit] Proximity 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 7,758 m (25,453 ft), one of the deepest locations of the Atlantic Ocean. It is also the largest mountain range known to humanity.

[edit] 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):

1. Jan Mayen (Beerenberg, 2277 m (at 71° 06' N, 08° 12' W), in the Arctic Ocean
2. Iceland (Hvannadalshnúkur in the Vatnajökull, 2109.6 m (at 64° 01' N, 16° 41' W), which the ridge runs through
3. Azores (Ponta do Pico or Pico Alto, on Pico Island, 2351 m, (at 38°28′0″N, 28°24′0″W)
4. Bermuda (Town Hill, on Main Island, 76 m (at 32° 18′ N, 64° 47′ W) (Bermuda was formed on the ridge, but is now considerably west of it)
5. Saint Peter and Paul Rocks (Southwest Rock, 22.5 m, at 00°55′08″N, 29°20′35″W)

Southern Hemisphere (South Atlantic Ridge):

1. Ascension Island (The Peak, Green Mountain, 859 m, at 7° 59' S, 14° 25' W)
2. Tristan da Cunha (Queen Mary's Peak, 2062 m, at 37° 05' S, 12° 17' W)
3. Gough Island (Edinburgh Peak, 909 m, at 40° 20' S, 10° 00' W)
4. Bouvet Island (Olavtoppen, 780 m, at 54° 24' S, 03° 21' E)

[edit] 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).

The ridge is about 2,500 meters (8,200 ft) below sea level, while its flank is about 5,000 meters deeper.

In 2007, oceanographic researchers were to explore what was described as a great, never-before-seen "wound" in the Earth's crust along the ridge between Tenerife and Barbados, where the rock of the Earth's mantle was exposed.

[edit] See also

• Atlantis Massif

[edit] References

• Evans, Rachel. "Plumbing Depths to Reach New Heights: Marie Tharp Explains Marine Geological Maps." The Library of Congress Information Bulletin. November 2002.

1. ^ Redfern, R.; 2001: Origins, the Evolution of Continents, Oceans and Life, University of Oklahoma Press, ISBN 1841881929, p. 26
2. ^ Alexander Hellemans and Brian Bunch, 1989, Timeline of Science, Sidgwick and Jackson, London
3. ^ 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
4. ^ Heezen, B. C. & Tharp, M.; 1954: Physiographic diagram of the western North Atlantic, Bulletin of the Geological Society of America 65, p. 1261
5. ^ 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
6. ^ Edgar W. Spencer, 1977, Introduction to the Structure of the Earth, 2nd edition, McGraw-Hill, Tokyo

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