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World Geography / Oceanography

Topographic Features of the Ocean Floor


    Topographic features of the ocean floor can be classified into 5 parts. Part of the coast which is submerged in the ocean is called Continental Shelf. Next to Continental Shelf, there exists Continental Slope. At the end of the Continental Slope, there will be a gently rising Continental Rise. Next to Continental Rise, there will be flat or gently sloping Abyssal Plain. Within the Abyssal plains, there exists Deep Sea Trenches. Ocean is supposed to be the source of origin of life. Here the biodiversity is more than that on the continents. Eastern and Western parts of the ocean bottom floors are almost mirror images of each other having similar topographic features.

    Ocean Floor Features

    • The Coast and the Continental Shelf is made of SIAL (Silicon - Aluminum) layer and the other parts of the ocean floor is made of SIMA (Silicon - Magnesium) layer.

    • Continental Shelf is gently sloped, sloping at an angle of less than 10. Originally, it was part of the continent but got submerged into the ocean over a period of time. The SIAL crust, which is located below the continental shelf, is rich in hydrocarbon reserves (mainly oil and natural gas).

    • Continental Slope is steeply sloping area, sloping at angle of 30 - 50. Here, deep narrow Canyons or Valleys known as submarine canyons, are present.

    • Continental Rise is part of Continental Slope and is angled around 10 - 30. It is a moderately sloping area. Continental Shelf, Continental Slope and Continental Rise comprise of 20% ocean bottom floor.

    • Abyssal Plains comprise of 80% ocean bottom floor. They are covered with extensive plains and are flat or gently sloping. In some areas, deep sea basins (depressions) are present and in some areas, some hills (abyssal hills of 1000 - 2000 m height) are present. Some Abyssal hills have flat tops known as Guyots.

    • Deep Narrow Trenches are very common in Pacific ocean having a depth of around 10000 - 11000 m, e.g. Mariana Trench (deepest place on earth surface), Kuril Trench, Challenger Deep, Romanche Trench, etc.

    • At midpoints of ocean bottom floor, the crust is highly fractured. Through these ruptured parts, the molten rock liquid comes from Asthenosphere and solidifies into new crust (Zone of formation of new crust). Some of the fluids form into ridges, which are called mid oceanic ridges (2 parallel ridges). In between these ridges, the new crust forms.

    • In Atlantic Ocean, the ridges are prominently formed. The mid Atlantic ridges divide the Western and the Eastern world into two equal halves. This Ridge is a continuous one but there exists interruption at the Equator in the form of Romanche Deep. The Ridge is quite massive and wide in nature in North almost like a Plateau (Telegraph Plateau) which facilitated the laying of telegraph line between New York and London. In southern hemisphere, there is broad and extensive Plateau known as Bromley Plateau.

    • In Pacific Ocean, we don't have continuous ridges. Only in South East Pacific ocean, the ridge is well developed and is known as South East Pacific Eye. In Indian Ocean, a continuous ridge is present only in between Lakshadweep and Chagos Islands.