Mid-Atlantic Ridge
Overview
 
The Mid-Atlantic Ridge (MAR) is a mid-ocean ridge
Mid-ocean ridge
A mid-ocean ridge is a general term for an underwater mountain system that consists of various mountain ranges , typically having a valley known as a rift running along its spine, formed by plate tectonics. This type of oceanic ridge is characteristic of what is known as an oceanic spreading...

, a divergent
Divergent boundary
In plate tectonics, a divergent boundary or divergent plate boundary is a linear feature that exists between two tectonic plates that are moving away from each other. Divergent boundaries within continents initially produce rifts which produce rift valleys...

 tectonic plate
Plate tectonics
Plate tectonics is a scientific theory that describes the large scale motions of Earth's lithosphere...

 boundary located along the floor of the Atlantic Ocean
Atlantic Ocean
The Atlantic Ocean is the second-largest of the world's oceanic divisions. With a total area of about , it covers approximately 20% of the Earth's surface and about 26% of its water surface area...

, and part of the longest mountain range in the world. It separates the Eurasian Plate
Eurasian Plate
The Eurasian Plate is a tectonic plate which includes most of the continent of Eurasia , with the notable exceptions of the Indian subcontinent, the Arabian subcontinent, and the area east of the Chersky Range in East Siberia...

 and North American Plate
North American Plate
The North American Plate is a tectonic plate covering most of North America, Greenland, Cuba, Bahamas, and parts of Siberia, Japan and Iceland. It extends eastward to the Mid-Atlantic Ridge and westward to the Chersky Range in eastern Siberia. The plate includes both continental and oceanic crust...

 in the North Atlantic, and the African Plate
African Plate
The African Plate is a tectonic plate which includes the continent of Africa, as well as oceanic crust which lies between the continent and various surrounding ocean ridges.-Boundaries:...

 from the South American Plate
South American Plate
The South American Plate is a continental tectonic plate which includes the continent of South America and also a sizeable region of the Atlantic Ocean seabed extending eastward to the Mid-Atlantic Ridge....

 in the South Atlantic. The Ridge extends from a junction with the Gakkel Ridge
Gakkel Ridge
The Gakkel 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 Arctic Ocean between Greenland and Siberia, and has a length of about 1,800 kilometers...

 (Mid-Arctic Ridge) northeast of Greenland
Greenland
Greenland is an autonomous country within the Kingdom of Denmark, located between the Arctic and Atlantic Oceans, east of the Canadian Arctic Archipelago. Though physiographically a part of the continent of North America, Greenland has been politically and culturally associated with Europe for...

 southward to the Bouvet Triple Junction
Bouvet Triple Junction
The Bouvet Triple Junction is a geologic triple junction of three tectonic plates located on the seafloor of the South Atlantic Ocean, named after Bouvet Island....

 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.
Encyclopedia
The Mid-Atlantic Ridge (MAR) is a mid-ocean ridge
Mid-ocean ridge
A mid-ocean ridge is a general term for an underwater mountain system that consists of various mountain ranges , typically having a valley known as a rift running along its spine, formed by plate tectonics. This type of oceanic ridge is characteristic of what is known as an oceanic spreading...

, a divergent
Divergent boundary
In plate tectonics, a divergent boundary or divergent plate boundary is a linear feature that exists between two tectonic plates that are moving away from each other. Divergent boundaries within continents initially produce rifts which produce rift valleys...

 tectonic plate
Plate tectonics
Plate tectonics is a scientific theory that describes the large scale motions of Earth's lithosphere...

 boundary located along the floor of the Atlantic Ocean
Atlantic Ocean
The Atlantic Ocean is the second-largest of the world's oceanic divisions. With a total area of about , it covers approximately 20% of the Earth's surface and about 26% of its water surface area...

, and part of the longest mountain range in the world. It separates the Eurasian Plate
Eurasian Plate
The Eurasian Plate is a tectonic plate which includes most of the continent of Eurasia , with the notable exceptions of the Indian subcontinent, the Arabian subcontinent, and the area east of the Chersky Range in East Siberia...

 and North American Plate
North American Plate
The North American Plate is a tectonic plate covering most of North America, Greenland, Cuba, Bahamas, and parts of Siberia, Japan and Iceland. It extends eastward to the Mid-Atlantic Ridge and westward to the Chersky Range in eastern Siberia. The plate includes both continental and oceanic crust...

 in the North Atlantic, and the African Plate
African Plate
The African Plate is a tectonic plate which includes the continent of Africa, as well as oceanic crust which lies between the continent and various surrounding ocean ridges.-Boundaries:...

 from the South American Plate
South American Plate
The South American Plate is a continental tectonic plate which includes the continent of South America and also a sizeable region of the Atlantic Ocean seabed extending eastward to the Mid-Atlantic Ridge....

 in the South Atlantic. The Ridge extends from a junction with the Gakkel Ridge
Gakkel Ridge
The Gakkel 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 Arctic Ocean between Greenland and Siberia, and has a length of about 1,800 kilometers...

 (Mid-Arctic Ridge) northeast of Greenland
Greenland
Greenland is an autonomous country within the Kingdom of Denmark, located between the Arctic and Atlantic Oceans, east of the Canadian Arctic Archipelago. Though physiographically a part of the continent of North America, Greenland has been politically and culturally associated with Europe for...

 southward to the Bouvet Triple Junction
Bouvet Triple Junction
The Bouvet Triple Junction is a geologic triple junction of three tectonic plates located on the seafloor of the South Atlantic Ocean, named after Bouvet Island....

 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 which includes the island of Iceland
Iceland
Iceland , described as the Republic of Iceland, is a Nordic and European island country in the North Atlantic Ocean, on the Mid-Atlantic Ridge. Iceland also refers to the main island of the country, which contains almost all the population and almost all the land area. The country has a population...

 is also known as the Reykjanes Ridge. The average spreading rate for the ridge is about 2.5 cm per year.

Discovery

A ridge under the Atlantic Ocean was first inferred by Matthew Fontaine Maury
Matthew Fontaine Maury
Matthew Fontaine Maury , United States Navy was an American astronomer, historian, oceanographer, meteorologist, cartographer, author, geologist, and educator....

 in 1850. The ridge was discovered during the expedition of HMS Challenger
Challenger expedition
The Challenger expedition of 1872–76 was a scientific exercise that made many discoveries to lay the foundation of oceanography. The expedition was named after the mother vessel, HMS Challenger....

 in 1872. A team of scientists on board, led by Charles Wyville Thomson
Charles Wyville Thomson
Sir Charles Wyville Thomson was a Scottish zoologist and chief scientist on the Challenger expedition.-Career:...

, discovered a large rise in the middle of the Atlantic while investigating the future location for a transatlantic telegraph cable
Transatlantic telegraph cable
The transatlantic telegraph cable was the first cable used for telegraph communications laid across the floor of the Atlantic Ocean. It crossed from , Foilhommerum Bay, Valentia Island, in western Ireland to Heart's Content in eastern Newfoundland. The transatlantic cable connected North America...

. The existence of such a ridge was confirmed by sonar in 1925 and was found to extend around the Cape of Good Hope
Cape of Good Hope
The Cape of Good Hope is a rocky headland on the Atlantic coast of the Cape Peninsula, South Africa.There is a misconception that the Cape of Good Hope is the southern tip of Africa, because it was once believed to be the dividing point between the Atlantic and Indian Oceans. In fact, the...

 into the Indian Ocean
Indian Ocean
The Indian Ocean is the third largest of the world's oceanic divisions, covering approximately 20% of the water on the Earth's surface. It is bounded on the north by the Indian Subcontinent and Arabian Peninsula ; on the west by eastern Africa; on the east by Indochina, the Sunda Islands, and...

 by the German Meteor expedition
German Meteor expedition
The German Meteor expedition was an oceanographic expedition that explored the South Atlantic ocean from the equatorial region to Antarctica in 1925–1927...

.

In the 1950s, mapping of the Earth’s ocean floors by Bruce Heezen
Bruce C. Heezen
Bruce Charles Heezen was an American geologist. He is most famous as being the leader of a team from Columbia University which mapped the Mid-Atlantic Ridge during the 1950s....

, Maurice Ewing
Maurice Ewing
William Maurice "Doc" Ewing was an American geophysicist and oceanographer.Ewing has been described as a pioneering geophysicist who worked on the research of seismic reflection and refraction in ocean basins, ocean bottom photography, submarine sound transmission , deep sea coring of the ocean...

, Marie Tharp
Marie Tharp
Marie Tharp was a geologist and oceanographic cartographer who, along with her colleague Bruce Heezen, mapped the ocean floor including the Mid-Oceanic Ridges, a line of undersea mountains.-Biography:...

 and others revealed the Mid-Atlantic Ridge to have a strange bathymetry
Bathymetry
Bathymetry is the study of underwater depth of lake or ocean floors. In other words, bathymetry is the underwater equivalent to hypsometry. The name comes from Greek βαθύς , "deep", and μέτρον , "measure"...

 of valleys and ridges, with its central valley being seismologically
Seismology
Seismology is the scientific study of earthquakes and the propagation of elastic waves through the Earth or through other planet-like bodies. The field also includes studies of earthquake effects, such as tsunamis as well as diverse seismic sources such as volcanic, tectonic, oceanic,...

 active and the epicentre of many earthquake
Earthquake
An earthquake is the result of a sudden release of energy in the Earth's crust that creates seismic waves. The seismicity, seismism or seismic activity of an area refers to the frequency, type and size of earthquakes experienced over a period of time...

s. Ewing and Heezen discovered the ridge to be part of a 40,000-km-long essentially continuous system of mid-ocean ridge
Mid-ocean ridge
A mid-ocean ridge is a general term for an underwater mountain system that consists of various mountain ranges , typically having a valley known as a rift running along its spine, formed by plate tectonics. This type of oceanic ridge is characteristic of what is known as an oceanic spreading...

s on the floors of all the Earth’s oceans. The discovery of this worldwide ridge system led to the theory of seafloor spreading
Seafloor spreading
Seafloor spreading is a process that occurs at mid-ocean ridges, where new oceanic crust is formed through volcanic activity and then gradually moves away from the ridge. Seafloor spreading helps explain continental drift in the theory of plate tectonics....

 and general acceptance of Wegener
Alfred Wegener
Alfred Lothar Wegener was a German scientist, geophysicist, and meteorologist.He is most notable for his theory of continental drift , proposed in 1912, which hypothesized that the continents were slowly drifting around the Earth...

's theory of continental drift
Continental drift
Continental drift is the movement of the Earth's continents relative to each other. The hypothesis that continents 'drift' was first put forward by Abraham Ortelius in 1596 and was fully developed by Alfred Wegener in 1912...

 and expansion as plate tectonics
Plate tectonics
Plate tectonics is a scientific theory that describes the large scale motions of Earth's lithosphere...

.

Notable features along the ridge

The Mid-Atlantic Ridge includes a deep rift valley which runs along the axis of the ridge along nearly its entire length. This rift marks the actual boundary between adjacent tectonic plates, where magma
Magma
Magma is a mixture of molten rock, volatiles and solids that is found beneath the surface of the Earth, and is expected to exist on other terrestrial planets. Besides molten rock, magma may also contain suspended crystals and dissolved gas and sometimes also gas bubbles. Magma often collects in...

 from the mantle reaches the seafloor, erupting as lava
Lava
Lava refers both to molten rock expelled by a volcano during an eruption and the resulting rock after solidification and cooling. This molten rock is formed in the interior of some planets, including Earth, and some of their satellites. When first erupted from a volcanic vent, lava is a liquid at...

 and producing new crustal material for the plates.

Near the equator
Equator
An equator is the intersection of a sphere's surface with the plane perpendicular to the sphere's axis of rotation and containing the sphere's center of mass....

, the Mid-Atlantic Ridge is divided into the North Atlantic Ridge and the South Atlantic Ridge by the Romanche Trench
Romanche Trench
The Romanche Trench, also called the Romanche Furrow or Romanche Gap, is the third deepest of the major trenches of the Atlantic Ocean, after the Puerto Rico Trench and the South Sandwich Trench. It bisects the Mid-Atlantic Ridge just north of the equator at the narrowest part of the Atlantic...

, a narrow submarine trench with a maximum depth of 7,758 m (25,453 ft), 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 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
    Jan Mayen
    Jan Mayen Island is a volcanic island in the Arctic Ocean and part of the Kingdom of Norway. It is long and 373 km2 in area, partly covered by glaciers . It has two parts: larger northeast Nord-Jan and smaller Sør-Jan, linked by an isthmus wide...

     (Beerenberg
    Beerenberg
    Beerenberg is a stratovolcano which forms the northeastern end of the Norwegian island of Jan Mayen. It is the world's northernmost subaerial active volcano...

    , 2277 m (at 71°06′N 08°12′W), in the Arctic Ocean
    Arctic Ocean
    The Arctic Ocean, located in the Northern Hemisphere and mostly in the Arctic north polar region, is the smallest and shallowest of the world's five major oceanic divisions...

  2. Iceland
    Iceland
    Iceland , described as the Republic of Iceland, is a Nordic and European island country in the North Atlantic Ocean, on the Mid-Atlantic Ridge. Iceland also refers to the main island of the country, which contains almost all the population and almost all the land area. The country has a population...

     (Hvannadalshnúkur
    Hvannadalshnúkur
    Hvannadalshnúkur or Hvannadalshnjúkur is a peak in the north-western rim of the Öræfajökull volcano in Iceland and the highest point of the island. An official measurement completed in August 2005 established its height as ....

     in the Vatnajökull
    Vatnajökull
    Vatnajökull is the largest glacier in Iceland. It is located in the south-east of the island, covering more than 8% of the country.-Size:With an area of 8,100 km², Vatnajökull is the largest ice cap in Europe by volume and the second largest in area Vatnajökull is the largest glacier in...

    , 2109.6 m (at 64°01′N 16°41′W), through which the ridge runs
  3. Azores
    Azores
    The Archipelago of the Azores is composed of nine volcanic islands situated in the middle of the North Atlantic Ocean, and is located about west from Lisbon and about east from the east coast of North America. The islands, and their economic exclusion zone, form the Autonomous Region of the...

     (Ponta do Pico or Pico Alto, on Pico Island
    Pico Island
    Pico Island , is an island in the Central Group of the Portuguese Azores noted for its eponymous volcano, Ponta do Pico, which is the highest mountain in Portugal, the Azores, and the highest elevation of the Mid-Atlantic Ridge...

    , 2351 m, (at 38°28′0"N 28°24′0"W)
  4. Bermuda
    Bermuda
    Bermuda is a British overseas territory in the North Atlantic Ocean. Located off the east coast of the United States, its nearest landmass is Cape Hatteras, North Carolina, about to the west-northwest. It is about south of Halifax, Nova Scotia, Canada, and northeast of Miami, Florida...

     (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
    Saint Peter and Paul Rocks
    The Saint Peter and Saint Paul Archipelago is a group of 15 small islets and rocks in the central equatorial Atlantic Ocean. It lies in the Intertropical Convergence Zone, a region of severe storms...

     (Southwest Rock, 22.5 m, at 00°55′08"N 29°20′35"W)

Southern Hemisphere (South Atlantic Ridge):
  1. Ascension Island
    Ascension Island
    Ascension Island is an isolated volcanic island in the equatorial waters of the South Atlantic Ocean, around from the coast of Africa and from the coast of South America, which is roughly midway between the horn of South America and Africa...

     (The Peak, Green Mountain, 859 m, at 07°59′S 14°25′W)
  2. Tristan da Cunha
    Tristan da Cunha
    Tristan da Cunha is a remote volcanic group of islands in the south Atlantic Ocean and the main island of that group. It is the most remote inhabited archipelago in the world, lying from the nearest land, South Africa, and from South America...

     (Queen Mary's Peak
    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 above sea level. It is named after Mary of Teck, the Queen consort of King George V...

    , 2062 m, at 37°05′S 12°17′W)
  3. Gough Island
    Gough Island
    Gough Island , also known historically as Gonçalo Álvares or Diego Alvarez, is a volcanic island in the South Atlantic Ocean. It is a dependency of Tristan da Cunha and part of the British overseas territory of Saint Helena, Ascension and Tristan da Cunha...

     (Edinburgh Peak, 909 m, at 40°20′S 10°00′W)
  4. Bouvet Island
    Bouvet Island
    Bouvet Island is an uninhabited Antarctic volcanic island in the South Atlantic Ocean, 2,525 km south-southwest of South Africa. It is a dependent territory of Norway and, lying north of 60°S latitude, is not subject to the Antarctic Treaty. The centre of the island is an ice-filled crater of an...

     (Olavtoppen, 780 m, at 54°24′S 03°21′E)


Geology

For a general explanation of mid-oceanic ridges, see mid-oceanic ridge and seafloor spreading
Seafloor spreading
Seafloor spreading is a process that occurs at mid-ocean ridges, where new oceanic crust is formed through volcanic activity and then gradually moves away from the ridge. Seafloor spreading helps explain continental drift in the theory of plate tectonics....



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
Asthenosphere
The asthenosphere is the highly viscous, mechanically weak and ductilely-deforming region of the upper mantle of the Earth...

 pushing the oceanic crust
Oceanic crust
Oceanic crust is the part of Earth's lithosphere that surfaces in the ocean basins. Oceanic crust is primarily composed of mafic rocks, or sima, which is rich in iron and magnesium...

 and lithosphere
Lithosphere
The lithosphere is the rigid outermost shell of a rocky planet. On Earth, it comprises the crust and the portion of the upper mantle that behaves elastically on time scales of thousands of years or greater.- Earth's lithosphere :...

.

This divergent boundary first formed in the Triassic
Triassic
The Triassic is a geologic period and system that extends from about 250 to 200 Mya . As the first period of the Mesozoic Era, the Triassic follows the Permian and is followed by the Jurassic. Both the start and end of the Triassic are marked by major extinction events...

 period when a series of three-armed
Triple junction
A triple junction is the point where the boundaries of three tectonic plates meet. At the triple junction a boundary will be one of 3 types - a ridge, trench or transform fault - and triple junctions can be described according to the types of plate margin that meet at them...

 graben
Graben
In geology, a graben is a depressed block of land bordered by parallel faults. Graben is German for ditch. Graben is used for both the singular and plural....

s coalesced on the supercontinent Pangaea
Pangaea
Pangaea, Pangæa, or Pangea is hypothesized as a supercontinent that existed during the Paleozoic and Mesozoic eras about 250 million years ago, before the component continents were separated into their current configuration....

 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 aulacogen
Aulacogen
In geology, an aulacogen is a failed arm of a triple junction of a plate tectonics rift system. A triple junction beneath a continental plate initiates a three way breakup of the continental plate. As the continental break-up develops one of the three spreading ridges typically fails or stops...

s
, and the aulacogens of the Mid-Atlantic Ridge eventually became many of the large river valleys seen along the Americas
Americas
The Americas, or America , are lands in the Western hemisphere, also known as the New World. In English, the plural form the Americas is often used to refer to the landmasses of North America and South America with their associated islands and regions, while the singular form America is primarily...

 and Africa
Africa
Africa is the world's second largest and second most populous continent, after Asia. At about 30.2 million km² including adjacent islands, it covers 6% of the Earth's total surface area and 20.4% of the total land area...

 (including the Mississippi River
Mississippi River
The Mississippi River is the largest river system in North America. Flowing entirely in the United States, this river rises in western Minnesota and meanders slowly southwards for to the Mississippi River Delta at the Gulf of Mexico. With its many tributaries, the Mississippi's watershed drains...

, Amazon River
Amazon River
The Amazon of South America is the second longest river in the world and by far the largest by waterflow with an average discharge greater than the next seven largest rivers combined...

 and Niger River
Niger River
The Niger River is the principal river of western Africa, extending about . Its drainage basin is in area. Its source is in the Guinea Highlands in southeastern Guinea...

).

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

The Fundy Basin
Fundy Basin
The Fundy Basin is a sediment-filled rift basin on the Atlantic coast of southeastern Canada. It contains three sub-basins; the Fundy sub-basin, the Minas Basin and the Chignecto Basin. These arms meet at the Bay of Fundy, which is contained within the rift valley. From the Bay of Fundy, the Minas...

 on the Atlantic coast of North America between New Brunswick
New Brunswick
New Brunswick is one of Canada's three Maritime provinces and is the only province in the federation that is constitutionally bilingual . The provincial capital is Fredericton and Saint John is the most populous city. Greater Moncton is the largest Census Metropolitan Area...

 and Nova Scotia
Nova Scotia
Nova Scotia is one of Canada's three Maritime provinces and is the most populous province in Atlantic Canada. The name of the province is Latin for "New Scotland," but "Nova Scotia" is the recognized, English-language name of the province. The provincial capital is Halifax. Nova Scotia is the...

 in Canada
Canada
Canada is a North American country consisting of ten provinces and three territories. Located in the northern part of the continent, it extends from the Atlantic Ocean in the east to the Pacific Ocean in the west, and northward into the Arctic Ocean...

is evidence of the ancestral Mid-Atlantic Ridge.

External links

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