Continental Shelf, Slope and Rise Continental shelf Extending seaward from the shore the continental shelf has a gradient of 1 in , to the shelf break, the outer limit, that has been set to where the gradient becomes an average of 1 in 20, usually with an average depth of m, down to the floor of the deep ocean where the predominant sediment is sand, and less commonly sand or mud. The average width of the shelf is 65 km, though it is much narrower in places, though it is as much as 10 times this width in other places such as the northeastern Bering Sea or the Arctic Shelf off Siberia. In a vertical cross-section of the ocean floor outward from the shore the shelf break is usually easily evident. There are many reasons why the fishing grounds of the world are situated on continental slope, among which are the proximity to estuaries, the dept the sunlight penetrates compared with the depth of the bottom, and on some shelves, the upwelling of nutrient-rich water, especially those off the western coasts of continents. The continental slope From the shelf to the ocean floor the average depth is about 4, m vertically, though it extends to more than 9, m vertically in a horizontal distance that is relatively short. Continental slopes are generally much steeper than the slopes between highlands and lowlands on the land.
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Continental Shelf There is no clear or well-defined line separating oceans from the continent. In fact, continents do not end abruptly at the shoreline. They slope seaward from coast to a point where the slope becomes very steep. This shallow submerged extension of the continent is called as the Continental Shelf. The depth usually ranges from to meters from the surface water. Their width also varies from a few kilometers to more than kilometers.
This variation can be seen even in the context of the Indian peninsula. Note: NIOS text mentions the opposite case Continental shelves are much narrow or absent in some continents, particularly where Fold Mountains run parallel or close to the coast.
The shallow water over the shelf enables sunlight to penetrate through the water to the bottom and encourages the growth of microscopic plants and animals called planktons, which are the food for fishes. Continental Shelves are of greater importance to man. Coral reefs are also common on continental shelves. One of the striking features of the continental shelf is the presence of submarine canyons which extend to the continental slope.
They are very similar to the gorges found on the continents. One of the reasons for the formation of the submarine canyon is the underwater landslide. The continental shelf is generally considered to be territorial water extents of the nations to which it adjoins. Continental Slope The continuous sloping portion of the continental margin, seaward of the continental shelf and extending down to the deep sea floor of the abyssal plain, is known as Continental Slope.
It extends between the depths of m to m. They have very little deposits of sediments on them due to their steepness and increasing distance from the land. Sea life is also far less here than on the shelf. The base of the continental slope will have deposits of sediments. This belt of sedimentary deposits forms the Continental Rise. Abyssal Plain Abyssal plains are the extremely flat and featureless plains of the deep ocean floor. Abyssal plains are considered as the levelest areas on the earth.
They cover a major portion of the ocean floors between the depths of m to m. Abyssal plains are as irregular as the continental plains with submarine plateaus, hills, guyots, and seamounts. The floor of the abyssal plain is covered by sediments.
The sediments which are formed from the remains of living things are called Oozes. Oozes can be seen in those seas which favour an abundant growth of organisms. Another type of sediments is red clay which is of volcanic origin or made up of tiny particles brought by wind and rivers. Some relief feature seen on abyssal plains are: a.
Submarine Ridges The oceanic mountains are called as submarine ridges. They are linear belts occurring near the middle of the oceans and are also called mid-oceanic ridges. The oceanic ridge is the site of frequent earthquakes. Volcanism is common in ocean ridges and it produces many relief features.
The Mid-Atlantic Ridge is the largest continuous submerged mountain ridge which runs from north to south in the Atlantic Ocean. At some places, the peaks rise above the sea surface to form Islands. Seamounts and Guyots Submerged volcanoes with sharp tops are called as seamounts. Sometimes they rise above the sea as isolated islands.
Hawaii and Tahiti Islands are such exposed tops of volcanoes. Seamounts with a flattened top are called as Guyots or Tablemounts.
They are generally called submarine trenches. These trenches are not always located in the middle of the ocean basins. They may be very close or parallel to the continents bordered by Fold Mountains. They are usually found adjacent to the areas of volcanic and earthquake activity.
Great earthquakes and tsunamis are born in them. The Pacific Ocean has the largest number of trenches. The Mariana trench in the Pacific Ocean is the deepest known part of the world. Article by: Jijo Sudarsan.
Ocean Floor: Everything you need to know