oceanic ridge


oceanic ridge
Continuous, submarine mountain chain extending approximately 50,000 mi (80,000 km) through all the world's oceans, separating them into distinct basins.

The main ridge extends down the middle of the Atlantic Ocean, passes between Africa and Antarctica, turns north to the Indian Ocean, then continues between Australia, New Zealand, and Antarctica and across the Pacific basin to the mouth of the Gulf of California. Lateral ridges extend from islands on the axis of the oceanic ridge to coasts of adjacent continents. The oceanic ridge system is the largest feature of the Earth's surface after the continents and the ocean basins themselves; it is explained by the theory of plate tectonics as a boundary between diverging plates where molten rock is brought up from deep beneath the Earth's crust. See also subduction zone.

* * *

 continuous submarine mountain chain extending approximately 80,000 km (50,000 miles) through all the world's oceans. Ridges separate the oceans into distinct basins and may or may not be seismically active.

      A brief treatment of oceanic ridges follows. For further discussion, see ocean: Oceanic ridges (ocean).

      The seismically active oceanic ridge is approximately 60,000 km (37,000 miles) long and extends down the axis of the entire Atlantic Ocean, passing midway between Africa and Antarctica and turning north to the centre of the Indian Ocean, where it branches, the main ridge continuing midway between Australia, New Zealand, and Antarctica to cross the east side of the Pacific Basin, running all the way to the mouth of the Gulf of California. The ridge is essentially a broad, enormous uplift sloping up from depths of more than 6,000 m (20,000 feet) in marginal basins to the crest of the ridge, which is almost everywhere less than 4,000 m (13,100 feet) in elevation, with crest mountains commonly rising to depths of 2,000 to 3,000 m (6,600 to 9,800 feet) but sometimes reaching above sea level. At intervals the ridge is crossed, usually at right angles, by large topographic disturbances called fracture zones that offset, or displace, the crest. These offsets are called transform faults. Shallow earthquake foci follow the crest: those along the axis of the ridge are caused by normal faulting, those on fracture zones by shearing. The oceanic ridge system is the largest feature of the Earth's surface after the continents and the ocean basins themselves; its volume exceeds 100,000,000 cubic km (25,000,000 cubic miles).

      Aseismic ridges (those having very few earthquakes or none at all) that extend wholly or partly from uplifted islands on the axis of the oceanic ridge to coasts of adjacent continents are called lateral ridges. Nearly straight ridges that terminate at one end in a young or active volcanic island are called linear chains.

      The pattern of ridges is so regular and their properties so constant that these features cannot be caused by chance. The only theory that satisfactorily explains their characteristics is that of plate tectonics. According to this theory, the outer 50 to 100 km (31 to 62 miles) of the Earth consists of a brittle shell that is broken into about 12 large plates and several small ones. Convection currents within the molten mantle (the next deeper layer within the Earth) cause these lithospheric plates to move slowly about relative to one another, and these motions generate the ridges. The oceanic ridge system and its branches mark boundaries along which magmatic upwelling (the rising of molten rock from deep beneath the crust) is splitting the ridge's crest and creating new ocean floor along the trailing edges of both plates. Particularly active upwellings at some places under the oceanic ridges are marked by active volcanoes, from which such islands as Iceland have formed.

      Lateral ridges are thought to have formed where this localized activity has been of long duration. They have been formed by the outpouring of lava throughout the time of expansion of an ocean basin and thus mark the locus of movement of the two plates away from the ridge crests. Linear ridges are considered to have a similar origin, except that in their case the source of the lava does not lie on the axis of a spreading ridge. Instead, if a single plate is driven over a hot spot (i.e., a magma-generating centre fixed in the deep mantle) from which the molten rock materials can penetrate to the surface, then those materials generate a single chain of progressively older volcanoes, which mark the direction of past motion of the plate over the hot spot.

* * *


Universalium. 2010.

Look at other dictionaries:

  • mid-oceanic ridge — [mid ō′shənmid ō΄shē an′ik] n. the continuous, double ridged chain of mountains on the ocean floor, extending through the middle of the Atlantic Ocean and into the Indian and Pacific oceans: also called mid ocean ridge [mid ō′shən] * * * …   Universalium

  • mid-oceanic ridge — [mid ō′shənmid ō΄shē an′ik] n. the continuous, double ridged chain of mountains on the ocean floor, extending through the middle of the Atlantic Ocean and into the Indian and Pacific oceans: also called mid ocean ridge [mid ō′shən] …   English World dictionary

  • mid-oceanic ridge — noun any of an interconnected system of broad submarine rises formed by plate tectonics Syn: mid ocean ridge …   Wiktionary

  • mid-oceanic ridge —   an elongated range of undersea mountains formed by the extrusion of lava, combined with the upward pressure of a convection plume, at a divergent plate margin …   Geography glossary

  • Oceanic trench — Oceanic crust is formed at an oceanic ridge, while the lithosphere is subducted back into the asthenosphere at trenches. The oceanic trenches are hemispheric scale long but narrow topographic depressions of the sea floor. They are also the… …   Wikipedia

  • Oceanic crust — Age of oceanic crust. The red is most recent, and blue is the oldest. 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… …   Wikipedia

  • oceanic — /oh shee an ik/, adj. 1. of, living in, or produced by the ocean: oceanic currents. 2. of or pertaining to the region of water lying above the bathyal, abyssal, and hadal zones of the sea bottom. Cf. neritic, pelagic. 3. immensely large; vast: an …   Universalium

  • ridge — ridgelike, adj. /rij/, n., v., ridged, ridging. n. 1. a long, narrow elevation of land; a chain of hills or mountains. 2. the long and narrow upper edge, angle, or crest of something, as a hill, wave, or vault. 3. the back of an animal. 4. any… …   Universalium

  • Oceanic lithosphere — is typically about 50 100 km thick (but beneath the mid ocean ridges is no thicker than the crust), while the continental lithosphere has a range in thickness from about 40 km to perhaps 200 km; the upper 30 to 50 km of the… …   Wikipedia

  • Oceanic core complex — An oceanic core complex (OCC), or megamullion, is a seabed geologic feature that forms a long ridge perpendicular to a mid ocean ridge. It contains smooth domes that are lined with transverse ridges like a corrugated roof. They can vary in size… …   Wikipedia


Share the article and excerpts

Direct link
Do a right-click on the link above
and select “Copy Link”

We are using cookies for the best presentation of our site. Continuing to use this site, you agree with this.