Mid-Atlantic Ridge

Full extent of the Mid-Atlantic Ridge

The Mid-Atlantic Ridge is a mountain range running mostly underwater and generally north-south through the middle of the Atlantic Ocean. If it were all above water, the ridge would be commonly regarded, at 16,000 km, as the world's longest continuous mountain span known all by one name. Its northern extent lies at approximately 87°N (about 330 km south of the North Pole); in the south it stretches to subantarctic Bouvet Island before turning east to become the Atlantic-Indian Ridge.

Part of the Earth's mid-oceanic ridge system, which reaches throughout all the world's oceans, the Mid-Atlantic Ridge was discovered in the 1950s by American geologists whose work led in the next decade to the theories of seafloor spreading, continental drift, and plate tectonics. The ridge is now known to be an oceanic rift separating 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. It actually sits on top of the "mid-Atlantic rise," a linear bulge running the length of the ocean with the ridge resting on the highest point of the bulge, which is thought to be caused by upward convective forces in the Earth's mantle.

Near the Equator, the ridge bends sharply in an S-curve and is dissected into the North Atlantic Ridge and South Atlantic Ridge by the Romanche Trench, a narrow submarine ravine with a maximum depth of 7,758 m, one of the deepest points in the Atlantic Ocean. The northernmost portion of the ridge passes under and beyond Iceland, where it is actually at the bottom of the Arctic Ocean rather than the Atlantic.

The highest summits of the Mid-Atlantic Ridge extend above the ocean's surface to form islands. The peaks that fall short of the ocean waves are called seamounts, of which there are many along the ridge.

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

• Jan Mayen (Norwegian, Beerenberg, 2,277 m, east of Greenland [in the Arctic Ocean])
• Iceland (Hvannadalshnúkur, 2,119 m, in Vatnajökull glacier)
• Azores (Portuguese, Ponta do Pico, 2,351 m, west of Iberian Peninsula)
• Saint Peter and Paul Rocks (Brazilian, Southwest Rock, 23 m, between Brazil and Liberia)

Southern Hemisphere (South Atlantic Ridge):

1. Ascension Island (The Peak, Green Mountain, 859 m, at 07°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)

These mountain ranges are where tectonic plates pull apart, this pulling motion creates cracks in the ocean floor called rift zones. As the plates pull apart, magma rises to fill in the spaces. Heat from the magma causes the crust on either side of the rifts to expand, forming the ridges. The ridge was discovered by Bruce Heezen and Marie Tharp in the 1950s. The discovery of this ridge led to the theory of [[]] and general acceptance of Wegener's theory of [[]]. According to plate tectonics, this ridge runs along a divergent boundary.

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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