The Mid-Atlantic Ridge is a mid-ocean ridge, a divergent tectonic plate or
constructive plate boundary located along the floor of the Atlantic Ocean,
and part of the longest mountain range in the world. In the North Atlantic, it
separates the Eurasian and North American Plates, whereas in the South
Atlantic it separates the African and South American Plates. The Ridge extends
from a junction with the Gakkel 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 that includes the island of
Iceland is also known as the Reykjanes Ridge. The ridge has an average
spreading rate of about 2.5 cm per year. Discovery
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 that the Mid-Atlantic Ridge had a
strange bathymetry of valleys and ridges, with its central valley being
seismologically active and the epicenter of many earthquakes. Ewing, Heezen and
Tharp discovered that the ridge is 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 in the modified form of plate tectonics. The ridge is central to
the breakup of the hypothetical supercontinent of Pangaea that began
some 180 million years ago. Notable features
The Mid-Atlantic Ridge includes a deep rift valley that 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,
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
The islands on or near the Mid-Atlantic Ridge, from north to south, with their
respective highest peaks and location, are:
Northern Hemisphere: Jan Mayen, in the Arctic Ocean
Iceland, through which the ridge runs Azores
Saint Peter and Paul Rocks Southern Hemisphere:
Ascension Island Saint Helena
Tristan da Cunha Gough Island
Bouvet Island Geology
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. The Fundy Basin on the Atlantic coast of North
America between New Brunswick and Nova Scotia in Canada is evidence of the
ancestral Mid-Atlantic Ridge. A section of the Mid-Atlantic ridge
occurs on land at Thingvellir, a popular destination for tourists in Iceland. The
easternmost edge of the North American plate can also be viewed there.
See also Atlantis Massif
References Bibliography
Evans, Rachel. "Plumbing Depths to Reach New Heights: Marie Tharp Explains Marine
Geological Maps." The Library of Congress Information Bulletin. November
2002. Notes
External links MAR-ECO, a Census of Marine Life project
on life along the Mid-Atlantic Ridge