- continental shelf
Physical Geog.the part of a continent that is submerged in relatively shallow sea.[1940-45]
* * *Broad, relatively shallow submarine platform that forms a border to a continent, typically extending from the coast to depths of 330–660 ft (100–200 m).Continental shelves average about 40 mi (65 km) in width. Almost everywhere they are simply a continuation of the continental landmass: narrow, rough, and steep off mountainous coasts but broad and comparatively level offshore from plains. Continental shelves are usually covered with a layer of sand, silts, and silty muds. Their surfaces feature small hills and ridges that alternate with shallow depressions and valley-like troughs. In a few cases, steep-walled V-shaped submarine canyons cut deeply into both the shelf and the slope below.
* * *▪ geologybroad, relatively shallow submarine platform that forms a border to a continent.A brief treatment of continental shelves follows. For full treatment, see ocean: Continental shelf (ocean).A continental shelf typically extends from the coast to depths of 100–200 m (330–660 feet). In nearly all instances, it ends at its seaward edge with an abrupt drop called the shelf break. Below this lies the continental slope, a much steeper zone that usually merges with a section of the ocean floor called the continental rise at a depth of roughly 4,000 to 5,000 m (13,000 to 16,500 feet).Continental shelves tend to vary greatly in width, but they average about 65 km (40 miles). Almost everywhere the shelves represent simply a continuation of the continental land mass beneath the ocean margins. Accordingly, they are narrow, rough, and steep off mountainous coasts but broad and comparatively level offshore from plains. The shelf along the mountainous western coast of the United States, for example, is narrow, measuring only about 32 km (20 miles) wide, whereas that fringing the eastern coast extends more than 120 km (75 miles) in width. Exceptionally broad shelves occur off northern Australia and Argentina.Continental shelves are usually covered with a layer of sand, silts, and silty muds. Their surfaces exhibit some relief, featuring small hills and ridges that alternate with shallow depressions and valleylike troughs. In a few cases, steep-walled V-shaped submarine canyons cut deeply into both the shelf and the slope below.Since the 1970s an increasing number of investigators have sought to explain the origin of continental shelves and their related structures in terms of plate tectonics. According to this theory, the shelves of the Pacific Ocean, for example, formed as the leading edges of continental margins on lithospheric plates that terminate either at fracture zones (sites where two such plates slide past each other) or at subduction zones (sites where one of the colliding plates plunges into the underlying partially molten asthenosphere and is consumed, while the overriding plate is uplifted). Shelves of such origin tend to be steep, deformed, and covered by a thin layer of erosional debris. The Atlantic continental shelves, on the other hand, show little or no tectonic deformation and bear a thick veneer of sedimentary material. They are thought to be remnants of the trailing edges of the enormous plates that split apart and receded many millions of years ago to form the Atlantic basin. As the edges of the plates gradually contracted and subsided, large amounts of sand, silts, and mud from the continents settled and accumulated along their seaward side.
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Look at other dictionaries:
continental shelf — n. a submerged shelf of land that begins at a continental shoreline, slopes downward gradually at an angle of about 0.1° for a variable distance, and ends at the top of a much steeper downward slope (continental slope) at an angle of about 3° to… … English World dictionary
continental shelf — plural continental shelves n technical the edge of a ↑continent where it slopes down steeply to the bottom of the ocean … Dictionary of contemporary English
continental shelf — noun count TECHNICAL the part of the edge of a CONTINENT that slopes gradually out into the ocean and ends in a sudden steep slope in very deep water … Usage of the words and phrases in modern English
continental shelf — ► NOUN ▪ an area of seabed around a large land mass where the sea is relatively shallow … English terms dictionary
Continental shelf — Marine habitats Anatomy of a continental shelf off the south eastern coast of the United States Littoral zone Intertidal zone … Wikipedia
continental shelf — UK / US noun [countable] Word forms continental shelf : singular continental shelf plural continental shelves science the part of the edge of a continent that slopes gradually out into the sea and ends in a sudden steep slope in very deep water … English dictionary
continental shelf — N UNCOUNT The continental shelf is the area which forms the edge of a continent, ending in a steep slope to the depths of the ocean. ...the deep water off the Continental Shelf … English dictionary
continental shelf — noun the relatively shallow (up to 200 meters) seabed surrounding a continent • Hypernyms: ↑ocean floor, ↑sea floor, ↑ocean bottom, ↑seabed, ↑sea bottom, ↑Davy Jones s locker, ↑Davy Jones * * * noun, pl ⋯ shelves [c … Useful english dictionary
continental shelf — Sea area extending beyond UK territorial waters sub divided and allocated to a number of Countries including certain European Union ( EU) Member States. Areas designated to the UK are called the UK Continental Shelf. HM Customs & Revenue Glossary … Financial and business terms
Continental Shelf — See Outer Continental Shelf … Ballentine's law dictionary