continental margin

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      A continental margin is the outer edge of continental crust abutting oceanic crust under coastal waters. It is one of the three major zones of the ocean floor, the other two being deep-ocean basins and mid-ocean ridges.
      The continental margin consists of three different features: the continental rise, the continental slope, and the continental shelf. Continental margins constitute about 28% of the oceanic area.


      Subzones



      The continental shelf is the relatively shallow water area found in proximity to continents; it is the portion of the continental margin that transitions from the shore out towards to ocean. Continental shelves are believed to make up 7% of the sea floor. The width of continental shelves worldwide varies in the range of 0.03–1500 km. The continental shelf is generally flat, and ends at the shelf break, where there is a drastic increase in slope angle: The mean angle of continental shelves worldwide is 0° 07′, and typically steeper closer to the coastline than it is near the shelf break.
      At the shelf break begins the continental slope, which can be 1–5 km above the deep-ocean floor. The continental slope often exhibits features called submarine canyons. Submarine canyons often cut into the continental shelves deeply, with near vertical sides, and continue to cut the morphology to the abyssal plain.
      These canyons are often V-shaped, and can sometime enlarge onto the continental shelf. At the base of the continental slope, there is a sudden decrease in slope angle, and the sea floor begins to level out towards the abyssal plain. This portion of the seafloor is called the continental rise, and marks the outermost zone of the continental margin.


      Types


      There are two types of continental margins: active and passive margins.
      Active margins are typically associated with lithospheric plate boundaries. These active margins can be convergent or transform margins, and are also places of high tectonic activity, including volcanoes and earthquakes. The West Coast of North America and South America are active margins. Active continental margins are typically narrow from coast to shelf break, with steep descents into trenches. Convergent active margins occur where oceanic plates meet continental plates. The denser oceanic crust of one plate subducts below the less dense continental crust of another plate. Convergent active margins are the most common type of active margin. Transform active margins are more rare, and occur when an oceanic plate and a continental plate are moving parallel to each other in opposite directions. These transform margins are often characterized by many offshore faults, which causes high degree of relief offshore, marked by islands, shallow banks, and deep basins. This is known as the continental borderland.
      Passive margins are often located in the interior of lithospheric plates, away from the plate boundaries, and lack major tectonic activity. They often face mid-ocean ridges. From this, comes a wide variety of features, such as low-relief land extending miles away from the beach, long river systems and piles of sediment accumulating on the continental shelf. The East Coast of the United States is an example of a passive margin. These margins are much wider and less steep than active margins.


      Sediment accumulation



      As continental crust weathers and erodes, it degrades into mainly sands and clays. Many of these particles end up in streams and rivers that then dump into the ocean. Of all the sediment in the stream load, 80% is then trapped and dispersed on continental margins. While modern river sediment is often still preserved closer to shore, continental shelves show high levels of glacial and relict sediments, deposited when sea level was lower. Often found on passive margins are several kilometres of sediment, consisting of terrigenous and carbonate (biogenous) deposits. These sediment reservoirs are often useful in the study of paleoceanography and the original formation of ocean basins. These deposits are often not well preserved on active margin shelves due to tectonic activity.


      Economic significance


      The continental shelf is the most economically valuable part of the ocean. It often is the most productive portion of the continental margin, as well as the most studied portion, due to its relatively shallow, accessible depths.
      Due to the rise of offshore drilling, mining and the limitations of fisheries off the continental shelf, the United Nations Convention on the Law of the Sea (UNCLOS) was established. The edge of the continental margin is one criterion for the boundary of the internationally recognized claims to underwater resources by countries in the definition of the "continental shelf" by the UNCLOS (although in the UN definition the "legal continental shelf" may extend beyond the geomorphological continental shelf and vice versa). Such resources include fishing grounds, oil and gas accumulations, sand, gravel, and some heavy minerals in the shallower areas of the margin. Metallic minerals resources are thought to also be associated with certain active margins, and of great value.


      See also


      Continent-ocean boundary
      Convergent boundary
      Passive margin


      References




      External links


      Map showing the locations of active and passive continental margins and the eight ocean regions

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    Active & Passive Continental Margins | Definition & Examples

    Nov 21, 2023 · A continental margin is the area where tectonic plates meet. This may result in the process of subduction, in which the denser oceanic plate is pushed down into the asthenosphere by the less dense ...

    Continental Rise | Definition, Formation & Characteristics

    Nov 21, 2023 · Continental Margin. Starting from the continental edge, where dry land turns to ocean, the first of three parts of the region called the continental margin, is the shallow, gentle descent of the ...

    Continental Slope | Definition, Features & Facts - Study.com

    Nov 21, 2023 · The continental slope is the portion of the margin that has a relatively steep incline starting at the edge of the continental shelf known as the continental shelf break, and gradually leveling ...

    What are the parts of the continental margin?

    The continental margin is, essentially, the hidden edges of continents that protrude into the ocean. This land feature is made up of the same components as the continents. Erosion has had an integral role in the formation of the continental margin.

    1. Draw a diagram of a passive continental margin and - Chegg

    Question: 1. Draw a diagram of a passive continental margin and another of an active continental margin. Label the following as appropriate on each diagram: continental and oceanic crust, continental shelf, continental slope, continental rise, ocean floor, shelf break, and trench. (10 points) 2 Why are Andean-type mountains usually volcanic?

    Solved Consider a continental margin that has a very broad

    Question: Consider a continental margin that has a very broad, flat continental shelf and a slope that descends 1 kilometer to the deep-ocean basin. Based on this information, this margin is _____. seismically activenear an offshore faulta continental borderlandlacking a continental risefar from an oceanic ridge

    Solved Which one of the following is part of the continental - Chegg

    Which one of the following is part of the continental margin? OA A) continental shelf B) accretionary wedge C) deep-sea fan D) continental trench

    What is the part of the continental margin that is nearest land?

    Continental Margin: When you go to the beach, the land slopes gently into the sea. This area where the land and water merge is called the continental margin and is made of three main zones, the continental shelf, the continental slope and the continental rise. Answer and Explanation:

    Solved Does this picture represent a passive continental - Chegg

    Question: Does this picture represent a passive continental margin or an active continental margin? Passive continental margin Active continental margin In the image above, identify the feature marked with a ?. In the diagram below, decide which type of continental margins is shown on each side. Passive continental margin Active continental margin

    Solved A passive margin is a continental margin which is NOT

    A passive margin is a continental margin which is NOT ALSO a plate boundary. An active margin is a continental margin that is also a plate boundary. Are the southeast and southwest margins of continental Africa... A) passive margins B) active margins O O