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Topic: Oceanic ridge

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Ocean Ridge

Gakkel Ridge

East Pacific Rise

Rift (geology)

Plate tectonics

Seafloor spreading

Oceanic trench

Chatham Rise

List of oceanic trenches

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Oceanic

Crust (geology)

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	Developing the theory [This Dynamic Earth, USGS]
		In 1961, scientists began to theorize that mid-ocean ridges mark structurally weak zones where the ocean floor was being ripped in two lengthwise along the ridge crest.
		Furthermore, the oceanic crust now came to be appreciated as a natural "tape recording" of the history of the reversals in the Earth's magnetic field.
		As old oceanic crust was consumed in the trenches, new magma rose and erupted along the spreading ridges to form new crust.
	pubs.usgs.gov /gip/dynamic/developing.html (1866 words)

	Plate Tectonics: Sea floor
		Seafloor spreading proposed that rising magma was forming new oceanic crust along the oceanic ridges and that old crust was destroyed at oceanic trenches.
		Oceanic rocks along the North American and African coastlines are approximately 180 Myrs old whereas rocks adjacent to the ridge may be less than one million years old.
		The presence of the older oceanic floor along the trenches was used to infer that the oceanic lithosphere was being consumed at the trenches.
	www.mhhe.com /earthsci/geology/mcconnell/pte/sfloor.htm (1890 words)

	Article 76 Unclos New Zealand - Law of the Sea
		Oceanic ridges are part of the deep ocean floor and are not part of the continental shelf.
		An example of a submarine ridge might be a transform ridge extending between the continental margin where it initiated, during the early phases of continental break up and the onset of sea floor spreading, and the deep ocean floor.
		The ridge complex is thought to have originated as a series of short spreading ridge segments connected by oceanic fracture zones that progressively rotated, lengthened, coalesced, and became uplifted as a result of changes in relative motion between the Australian and Pacific plates.
	www.gns.cri.nz /research/marine/unclos/ridges.html (2226 words)

	Oceanography 2
		Morgan proposed that opposing plates along an oceanic ridge crest offset by fracture zones are divided by the spreading centres and transform faults.
		The cause of the subsidence is attributed to the sinking of the seafloor as it moves down the flanks of an oceanic ridge.
		At slower rates, faulting of the oceanic crust is a dominant factor in forming the relief, and the relief of the hills is greater as the rate is slower.
	www.crystalinks.com /ocean2.html (4717 words)

	Ocean Basins
		Oceanic Ridges - these are the oceanic spreading centers where a relatively small range of chemical compositions of basalts are erupted to form the basaltic layer of the oceanic crust.
		Oceanic Islands - these are islands in the ocean basins that generally occur away from plate boundaries, and are often associated with hot spots, as discussed previously.
		Similarly contamination with oceanic sediment is unlikely because, even though ocean sediment exists in the deep ocean basins, the OIB magmas are not likely to come in contact with much sediment because they are passing through large volcanic structures to reach the surface of the island.
	www.tulane.edu /~sanelson/geol212/ocean_basins.htm (6207 words)

	Mid-ocean_ridge (Site not responding. Last check: 2007-10-14)
		A mid-ocean ridge or mid-oceanic ridge is an uplifting of the ocean floor that occurs when convection currents beneath the ocean bed force magma up where two tectonic plates meet at a divergent boundary.
		The mid-ocean ridges of the world are connected and form a single global mid-oceanic ridge system that is part of every ocean and also by far the longest mountain range on Earth.
		Because the mid-ocean ridge is underwater, and not just underwater, but submerged at very deep depths in the middle of the oceans, its existence was not even known until the 1950s, when it was discovered through surveys of the ocean floor conducted by research ships.
	www.apawn.com /search.php?title=Mid-ocean_ridge (372 words)

	Plate Tectonics
		If new oceanic crust and lithosphere is continually being created at the oceanic ridges, the oceans should be expanding indefinitely, unless there were a mechanism to destroy the oceanic lithosphere.
		These are oceanic ridges where new oceanic lithosphere is created by upwelling mantle that melts, resulting in basaltic magmas which intrude and erupt at the oceanic ridge to create new oceanic lithosphere and crust.
		Because the oceanic ridges are areas of young crust, there is very little sediment accumulation on the ridges.
	www.tulane.edu /~sanelson/geol111/pltect.htm (3395 words)

	oceanic - Search Results - MSN Encarta
		Oceanic Art, works of art produced by the indigenous peoples of the Pacific Islands from the beginnings of human settlement to the present,...
		Oceanic Ridge, term usually taken to mean mid-ocean ridges, which are broad undersea mountain ranges typically occurring far from land.
		Oceanic Languages, group of about 500 languages belonging to the Austronesian language family.
	uk.encarta.msn.com /oceanic.html (144 words)

	ch4_Sea floor spreading
		Oceanic ridges (white) form a network of submarine mountains on the sea floor.
		The age of the ocean floor varies with location and is consistently youngest at the oceanic ridges and older along the ocean margins.
		Oceanic rocks along the North American and African coastlines are approximately 180 My old whereas rocks adjacent to the ridge may be less than one million years old.
	www.mhhe.com /earthsci/geology/mcconnell/plate_tectonics/sfloor.htm (1720 words)

	Plate Tectonics Basics
		Recognizing these anomalies and interpreting them in terms of new sea floor generation at mid-oceanic ridges was one of the key elements for the formulation of the plate tectonics theory.
		Scientists also began to realize that the youngest regions of the ocean floor were along the mid-oceanic ridges, and that the age of the ocean floor increased as the distance from the ridges increased.
		As the ocean floor is spread, apart cracks appear in the middle of the ridges allowing molten magma to surface through the cracks to form the newest ocean floor.
	www.indiana.edu /~geol105/images/gaia_chapter_3/plate_tectonics_basics.htm (1098 words)

	OceanLink
		Rift valleys along oceanic ridge crests indicate tension, are bounded by normal faults, and are floored by recently-erupted basaltic lava flows.
		Whereas oceanic ridges indicate tension, continental mountains indicate compressional forces are squeezing the land together.
		Moving across the ocean floor perpendicularly to the oceanic ridges, magnetometers alternately record stronger (positive) and weaker (negative) magnetic fields (called magnetic anomalies) in response to the influence of the sea floor rocks.
	www.jbpub.com /oceanlink/4e/lectureoutlines.cfm?chapter=3&step=2 (626 words)

	Oceanic trench Summary
		Trenches form where oceanic lithosphere is subducted at a convergent plate margin, presently at a global rate of about a tenth of a square meter per second.
		Accretionary prisms grow by frontal accretion, whereby sediments are scraped off, bulldozer-fashion, near the trench, or by underplating of subducted sediments and perhaps oceanic crust along the shallow parts of the subduction decollement.
		The average forearc is underrun by a solid volume of oceanic sediment that is 400 m thick.
	www.bookrags.com /Oceanic_trench (4120 words)

	Learning Objectives
		The idea that the sea floor spread away from mid-oceanic ridges and was subducted beneath a continent or island arc as a result of mantle convection was proposed by Harry Hess in the early 1960s.
		Sea-floor spreading explains the young age of the sea floor, loss of older oceanic crust, lack of pelagic sediment on the ridge crest, and increasingly older oceanic crust away from the ridge crest.
		Ridge crests, trenches, transform faults, and their associated features are capable of migration in response to changing mantle conditions.
	highered.mcgraw-hill.com /sites/0072826967/student_view0/chapter4/learning_objectives.html (1097 words)

	Mid-oceanic ridge - CreationWiki
		Mid-oceanic ridge data gathered by oceanographic surveys conducted by many nations led to the discovery that a great mountain range on the ocean floor virtually encircled the Earth.
		Called the global mid-ocean ridge, this immense submarine mountain chain -- more than 50,000 kilometers (km) long and, in places, more than 800 km across -- zig-zags between the continents, winding its way around the globe like the seam on a baseball.
		Rising an average of about 4,500 meters(m) above the sea floor, the mid-ocean ridge overshadows all the mountains in the United States except for Mount McKinley (Denali) in Alaska (6,194 m).
	creationwiki.org /Mid-oceanic_ridge (169 words)

	seafloor features text
		The Atlantic Ocean is the youngest of the three and is dominated by a central oceanic ridge and by abyssal plains of fine sediment.
		oceanic ridge system is the most pronounced tectonic feature on earth.
		The combined ridges are more than 60,000 km in length, with an area of 23% of the earth's surface, almost equal to the total area of the continents.
	geology.uprm.edu /Morelock/GEOLOCN_/seafloor.htm (962 words)

	The Modern Theory of Plate Tectonics
		At the mid oceanic ridges, water soaks into the oceanic crust, is heated by the underlying magma, and rises back to the sea floor as superheated "geysers" or hydrothermal vents.
		Since the new plate boundary is in the center of the mid oceanic ridge, the joint between the continental crust and the new oceanic crust is called the Passive Margin of the continent.
		This may be related to the increasing density of the crust as it cools, or with the increasing distance from the mid-oceanic ridge and the movement of currents in the upper mantle.
	faculty.weber.edu /bdattilo/shknbk/notes/plts.htm (1102 words)

	10(i) Plate Tectonics
		The polarity patterns found in the rocks at the ocean floor seemed to mirror themselves either side of the mid-oceanic ridge found at the centers of the ocean basins.
		Subsequent research discovered that the Earth's surface was composed of a number of oceanic and continental plates that float on top of the asthenosphere (see Figure 10i-3).
		Oceanic crust is destroyed at areas where this crust type becomes subducted under lighter continental crust.
	www.physicalgeography.net /fundamentals/10i.html (1007 words)

	10(p) Physiography of the Ocean Basins
		Mid-oceanic ridge is normally found rising above the ocean floor at the center of the ocean basins (see Figure 10p-1).
		In the center of the mid-oceanic ridge is a rift valley, between 30 to 50 kilometers wide, that dissects 1000 to 3000 meters deep into the ridge system.
		The creation of new oceanic crust at the mid-oceanic ridge moves the continents across the Earth's surface and creates zones of subduction.
	www.physicalgeography.net /fundamentals/10p.html (1036 words)

	Marine Geology: Plate Tectonics (Site not responding. Last check: 2007-10-14)
		Oceanic crust is the main crustal unit under Earth's oceans.
		Oceanic crust has lots of silica and iron and may be referred to as simatic.
		At oceanic ridges most of the crustal movement is near the surface as sea-floor spreading causes plates to move apart and new crust is formed by magma pushing up from the mantle.
	www.biosbcc.net /ocean/marinesci/02ocean/mgtectonics.htm (1914 words)

	Viewing the Morphology of the Mid-Atlantic Ridge From a New Perspective
		The along-axis orientation of the ridge mimics neighboring faults and fissures, and it is inferred to have erupted from similar fissures.
		Hummocks and hummocky ridges are produced as the eruption becomes confined to several discrete vents, similar to subaerial spatter cones or spatter ramparts that form along fissures (Figure 4).
		Based on this model, the hummocks and hummocky ridges that dominate the small-scale volcanic morphology of the AVR in the 29° N segment are formed by the focusing of fissure eruptions to several vents; the seamount is formed by the rapid evolution of an eruption to a single vent.
	www.agu.org /sci_soc/eosdksmith.html (2756 words)

	The Ocean Floor and it's Evolution
		Away from the ridge crest the volcanic and seismic activity and the elevation decreases.
		Portion of ocean floor extending from the ridge on one side to a trench or continental margin on the other.
		Sediments directly from the continents and from settling of suspended sediment in the ocean fill in the irregularities of the ocean bottom and give this region its flat character.
	core.ecu.edu /geology/woods/SEAFLOORlecture.htm (1179 words)

	Amateur Geologist Structured Geological Glossary: The Ocean
		The oceanic crust is mostly basalt, undeformed, and, due to plate tectonics, younger than 150 million years old.The major features of the ocean floor are oceanic ridge, abyssal floor, seamount, trenches and continental margin.
		An oceanic water wave with a wavelength on the order of 30 meters or more and a height of perhaps 2 meters or less that may travel great distances from its source.
		The relatively flat surface of the deep ocean floor spreading from an oceanic ridge.
	www.amateurgeologist.com /content/glossary/ocean/ocean.html (1275 words)

	The Hindu : Role of plate tectonics in earthquake occurrence (Site not responding. Last check: 2007-10-14)
		Actually the rocks are in the form of stripes and parallel to the ridge with the age of these stripes progressively increasing away from either side of the ridge crest.
		It was found that the oceanic crust moving in a conveyor belt- like motion finally descends into the earth along the oceanic trenches-very deep (several hundreds of kilometers into the earth), narrow canyons along the rim of the Pacific Ocean basin.
		Plates and oceanic crust that are in constant motion are consumed or adjusted to maintain the same size of the earth.
	www.hinduonnet.com /2001/02/01/stories/08010002.htm (1821 words)

	Tectonic Plates
		With the exception of the dominantly oceanic Pacific Plate and some of the smaller plates, these plates consist of both oceanic and continental crust and upper mantle material.
		For example, the North American plate consists of the North American continental mass and the oceanic crust extending out form the eastern edge of the North American continent to the spreading ridge of the Mid-Atlantic ocean ridge.
		According to plate tectonic theory, the outer 400 km of the Earth is is broken into two zones, the upper, thinner, rigidly deforming lithosphere 100 km or less in thickness and the lower ductilely deforming asthenosphere.
	www.utexas.edu /tmm/npl/mineralogy/Mineral_Genesis/defintectonicplates.htm (425 words)

	Glossary (Site not responding. Last check: 2007-10-14)
		A margin consisting of a continental shelf, a continental slope, and an oceanic trench.
		A resistant ridge of calcium carbonate formed on the sea floor by corals and coralline algae.
		Rift valleys are found at diverging plate boundaries on continents and along the crest of the mid-oceanic ridge.
	highered.mcgraw-hill.com /sites/0072826967/student_view0/chapter3/glossary.html (492 words)

	Rift Summary
		This mountain chain, or mid-ocean ridge system, encircles the Earth like the seams on a baseball and is one of Earth's dominant features, extending over an area greater than all the major land mountain ranges combined and covering a third of the ocean basins.
		Ridge systems with fast spreading rates exhibit low relief, no central valley, high heat flow, earthquakes of magnitude 4.5 or less and are often associated with active hydrothermal vents.
		After passively traveling thousands of miles away from the oceanic ridge where it formed and subsiding hundreds or thousands of feet, only the tallest of these submarine mountains is high enough to rise above the thick sediment that covers seafloor 10s of millions of years old.
	www.bookrags.com /Rift (2002 words)

	Plate Tectonics
		Ocean floor magnetic surveys show youngest crust is located adjacent to the spreading ridges and that the age of the crust increases with distance away from the ridge.
		Theory that the ocean floors are spreading apart and moving away from the oceanic ridges (propelled by thermal convection cells in the mantle) and that ocean crust is created at oceanic ridges and destroyed by subduction in deep ocean trenches.
		Occur in oceanic crust (oceanic ridges) and in continental crust (rift valleys).
	www.geo.ua.edu /intro03/Plate.html (2149 words)

	Plume-Ridge Interaction Workshop Abstracts (Site not responding. Last check: 2007-10-14)
		Oceanic plates form, age and subduct in a continuous process of opening and closing of ocean basins that involves mainly the upper mantle.
		The principal effect of ridge migration is to introduce a strong asymmetry in the shape of the plume pancake, which is no longer the same on both sides of the ridge.
		For each of these ridge systems, the locations of ridge segments and offsets are compiled from the literature, or picked from satellite gravity maps where published detailed studies are unavailable, and then segment and offset lengths are statistically analyzed so that model geometries have realistic ridge configurations.
	ridge.oce.orst.edu /meetings/PRIworkshop/PRIabstracts.html (18848 words)

	Vic Camp - spreading center volcanism
		The rise of this hot mantle provides thermal buoyancy to the ridge area and this is the reason that they stand as high ridges in the center of ocean basins.
		Oceanic crust is youngest near the ridge, but it becomes progressively older away from the spreading center due to divergence of the plates over time.
		Whereas oceanic crust is generated at divergent plate margins, it is consumed at convergent plate margins.
	www.geology.sdsu.edu /how_volcanoes_work/seafloorvol_page.html (363 words)

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