On the basis of the depth, the ocean floor can be divided into four zones, parts or relief features. They are,
1. The continental Shelf: The gently sloping portion of the continent or land that **** submerged below other sea is called the continental shelf. The continental shelf has a very gentle slope. It extends form the shore line to depths between 1 80 and 200 meters.
Average width of the continental shelves is about 48km. The extent of the continental shelf depends on the relief of the broadening land masses. If the coastal area is a plateau area, the continental shelf will be very broad. On the other hand, if the coastal region is hilly or mountainous, the continental shelf will be very narrow or even absent for example the Atlantic Ocean has 2.3%, the Pacific Ocean has 5.7% and the India Ocean has 4.2%.
2. The continental slope: The zone of steep slope that descends from the edge of the continental sheif to the deep sea plains is called ‘continental slope”. It is the transitional zone lying between the continental shelf and the deep sea plains. The continental slope is very steep. It extends from 182 meters to 3,600 meters. The angle of the continental slope is 2 to 5 degre3es or even more. It occupies only 8.5% of the total area of the ocean floor. But it varies from ocean to ocean. The Atlantic Ocean has broader continental slopes and accounts for 12.4%. But it is 7% of the Pacific Ocean and 6.5% of the Indian Ocean.
3. The deep sea plaitis: The level and rolling areas of the ocean floor are generally called deep sea plains or abyssal plains or the ocean plains. They lie between 3.000 and 6.000 meters below other surface of the ocean. They occupy vast area of the ocean floor and account for about 82.7% of the total sea floor. They cover about 90% in the Indian Ocean. Their depth ranges from 5.000 to 6,000 meters. They are covered by oozes, which are the *** of deep sea creatures and plants, and of red volcanic dust,
4. The Ocean Deeps: The long narrow and deep troughs on the ocean floor are known as ‘ocean deep’ or trough’. They cover only 1% of the ocean floor. They are most common neat the coasts where young fold mountains, volcanoes and earthquakes abound. Some they are tectonic in origin. They are the deepest portions of the ocean. Deeps may be caused due to tectonic forces, i.e. faulting earthquakes etc.-There are 57 known deeps. Of these 32 are found in Pacific Ocean, 19 m the Atlantic Ocean and 6 in the Indian Ocean. The deepest trench in the world is Challenger deep located in Mariana Trench to the west of Philippines in the North Pacific Ocean.
