The Mid-Atlantic Ridge is a
mid-ocean ridge
A mid-ocean ridge (MOR) is a seafloor mountain system formed by plate tectonics. It typically has a depth of about and rises about above the deepest portion of an ocean basin. This feature is where seafloor spreading takes place along a div ...
(a
divergent or constructive
plate boundary) located along the floor of the
Atlantic Ocean
The Atlantic Ocean is the second-largest of the world's five oceans, with an area of about . It covers approximately 20% of Earth's surface and about 29% of its water surface area. It is known to separate the " Old World" of Africa, Europe ...
, and part of the
longest mountain range in the world. In the North Atlantic, the ridge separates the
North American from the
Eurasian Plate and the
African Plate, north and south of the
Azores Triple Junction respectively. In the South Atlantic, it separates the
African and
South American plates. The ridge extends from a junction with the
Gakkel Ridge
The Gakkel Ridge (formerly known as the Nansen Cordillera and Arctic Mid-Ocean Ridge) is a mid-oceanic ridge, a divergent tectonic plate boundary between the North American Plate and the Eurasian Plate. It is located in the Eurasian Basin of the ...
(Mid-Arctic Ridge) northeast of
Greenland
Greenland ( kl, Kalaallit Nunaat, ; da, Grønland, ) is an island country in North America that is part of the Kingdom of Denmark. It is located between the Arctic and Atlantic oceans, east of the Canadian Arctic Archipelago. 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, for example in
Iceland
Iceland ( is, Ísland; ) is a Nordic island country in the North Atlantic Ocean and in the Arctic Ocean. Iceland is the most sparsely populated country in Europe. Iceland's capital and largest city is Reykjavík, which (along with its ...
. The ridge has an average spreading rate of about per year.
Discovery
A ridge under the northern Atlantic Ocean was first inferred by
Matthew Fontaine Maury in 1853, based on soundings by the
USS ''Dolphin''. The existence of the ridge and its extension into the South Atlantic was confirmed during the
expedition of HMS ''Challenger'' in 1872.
A team of scientists on board, led by
Charles Wyville Thomson
Sir Charles Wyville Thomson (5 March 1830 – 10 March 1882) was a Scottish natural historian and marine zoologist. He served as the chief scientist on the Challenger expedition; his work there revolutionized oceanography and led to his knigh ...
, 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
Cape Agulhas into the
Indian Ocean
The Indian Ocean is the third-largest of the world's five oceanic divisions, covering or ~19.8% of the water on Earth's surface. It is bounded by Asia to the north, Africa to the west and Australia to the east. To the south it is bounded by ...
by the
German Meteor expedition.
In the 1950s,
mapping of the Earth's ocean floors by
Marie Tharp,
Bruce Heezen,
Maurice Ewing, and others revealed that the Mid-Atlantic Ridge had a strange
bathymetry
Bathymetry (; ) is the study of underwater depth of ocean floors ('' seabed topography''), lake floors, or river floors. In other words, bathymetry is the underwater equivalent to hypsometry or topography. The first recorded evidence of water ...
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 (25,000 mile) long essentially continuous system of
mid-ocean ridge
A mid-ocean ridge (MOR) is a seafloor mountain system formed by plate tectonics. It typically has a depth of about and rises about above the deepest portion of an ocean basin. This feature is where seafloor spreading takes place along a div ...
s 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 for nearly its entire length. This rift marks the actual boundary between adjacent tectonic plates, where
magma
Magma () is the molten or semi-molten natural material from which all igneous rocks are formed. Magma is found beneath the surface of the Earth, and evidence of magmatism has also been discovered on other terrestrial planets and some natura ...
from the
mantle
A mantle is a piece of clothing, a type of cloak. Several other meanings are derived from that.
Mantle may refer to:
*Mantle (clothing), a cloak-like garment worn mainly by women as fashionable outerwear
**Mantle (vesture), an Eastern Orthodox ve ...
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 , 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 (North Atlantic Ridge):
#
Jan Mayen (
Beerenberg, 2277 metres (7470') (at ), in the
Arctic Ocean
#
Iceland
Iceland ( is, Ísland; ) is a Nordic island country in the North Atlantic Ocean and in the Arctic Ocean. Iceland is the most sparsely populated country in Europe. Iceland's capital and largest city is Reykjavík, which (along with its ...
(
Hvannadalshnúkur at
Vatnajökull, 2109.6 metres (6921') (at ), through which the ridge runs
#
Azores
)
, motto =( en, "Rather die free than subjected in peace")
, anthem= ( en, "Anthem of the Azores")
, image_map=Locator_map_of_Azores_in_EU.svg
, map_alt=Location of the Azores within the European Union
, map_caption=Location of the Azores wi ...
(
Ponta do Pico
Mount Pico ( pt, Montanha do Pico) is a currently quiescent stratovolcano located on Pico Island, in the mid-Atlantic archipelago of the Azores. It is the highest mountain in Portugal, at above sea level, and is one of the highest Atlantic mount ...
or Pico Alto, on
Pico Island, 2351 metres (7713'), (at )
#
Saint Peter and Paul Rocks (Southwest Rock, 22.5 metres (74'), at )
Southern Hemisphere (South Atlantic Ridge):
#
Ascension Island
Ascension Island is an isolated volcanic island, 7°56′ south of the Equator in the South Atlantic Ocean. It is about from the coast of Africa and from the coast of South America. It is governed as part of the British Overseas Territory of ...
(The Peak, Green Mountain, 859 metres (2818'), at )
#
Saint Helena (
Diana's Peak, 818 metres (2684') at )
#
Tristan da Cunha (
Queen Mary's Peak
Queen Mary's Peak is the summit of the island of Tristan da Cunha, in the South Atlantic Ocean. It has an elevation of 2,062 metres (6,765 ft) above sea level. It is named after Mary of Teck, the Queen consort of King George V. It is the hi ...
, 2062 metres (6765'), at )
#
Gough Island (
Edinburgh Peak, 909 metres (2982'), at )
#
Bouvet Island (
Olavtoppen
Olavtoppen, occasionally anglicised as Olav Peak, is the highest point of Bouvet Island, a volcanic island and dependency of Norway, and the remotest island on Earth. Olavtoppen is located north of the center of the island, immediately south of ...
, 780 metres (2560'), at )
Iceland
The submarine section of the Mid-Atlantic Ridge close to southwest Iceland is known as the Reykjanes Ridge. The Mid-Atlantic Ridge runs through Iceland where the ridge is also known as the ''Neovolcanic Zone''. In the north of Iceland the
Tjörnes Fracture Zone connects Iceland to the
Kolbeinsey Ridge.
Geology
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
The Triassic ( ) is a geologic period and system which spans 50.6 million years from the end of the Permian Period 251.902 million years ago ( Mya), to the beginning of the Jurassic Period 201.36 Mya. The Triassic is the first and shortest per ...
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
Africa is the world's second-largest and second-most populous continent, after Asia in both cases. At about 30.3 million km2 (11.7 million square miles) including adjacent islands, it covers 6% of Earth's total surface area ...
(including the
Mississippi River,
Amazon River and
Niger River). The
Fundy Basin on the Atlantic coast of North America between
New Brunswick
New Brunswick (french: Nouveau-Brunswick, , locally ) is one of the thirteen provinces and territories of Canada. It is one of the three Maritime provinces and one of the four Atlantic provinces. It is the only province with both English and ...
and
Nova Scotia in
Canada
Canada is a country in North America. Its ten provinces and three territories extend from the Atlantic Ocean to the Pacific Ocean and northward into the Arctic Ocean, covering over , making it the world's second-largest country by to ...
is evidence of the ancestral Mid-Atlantic Ridge.
See also
*
Atlantis Massif
The Atlantis Massif is a prominent undersea massif in the North Atlantic Ocean. It is a dome-shaped region approximately across and rising about from the sea floor. It is located at approximately 30°8′N latitude 42°8′W longitude; just eas ...
*
Canadian Arctic Rift System
The Canadian Arctic Rift System is a major North American geological structure extending from the Labrador Sea in the southeast through Davis Strait, Baffin Bay and the Arctic Archipelago in the northwest. It consists of a series of interconnecte ...
*
Central Atlantic Magmatic Province
*
Charlie-Gibbs Fracture Zone
*
East Pacific Rise
The East Pacific Rise is a mid-ocean rise (termed an oceanic rise and not a mid-ocean ridge due to its higher rate of spreading that results in less elevation increase and more regular terrain), a divergent tectonic plate boundary located alon ...
*
Fifteen-Twenty Fracture Zone
*
Project FAMOUS
*
Researcher Ridge
References
Bibliography
* Evans, Rachel.
Plumbing Depths to Reach New Heights: Marie Tharp Explains Marine Geological Maps. ''The Library of Congress Information Bulletin.'' November 2002.
External links
MAR-ECO, a Census of Marine Life project on life along the Mid-Atlantic Ridge
{{Authority control
Mesozoic rifts and grabens
Cenozoic rifts and grabens