Ocean Floor

Geography is an interesting subject which covers land (lithosphere), water (hydrosphere) and air (atmosphere). Hope you have gone through our easy-to-learn notes covering important land features. Now let’s see how to learn fast the concepts associated with hydrosphere. Let’s start from ocean floor first.

Earth – the water planet We know that our earth is the only planet in the solar system which has water in abundance; hence, it is often called as ‘water planet’. About 71% of the earth’s surface is covered by water (3/5 of Northern Hemisphere and 4/5 of Southern Hemisphere is covered by water). Similar to the continental landforms which have been discussed in previous articles, oceans also contain a variety of landforms.

Oceanic land-forms (submarine relief)

• ➢ There are mountains, basins, plateaus, ridges, canyons and trenches beneath the ocean water too.
• ➢ These relief features found on the ocean floor are called Submarine Relief.
• ➢ The ocean basins are broadly divided into four major subdivisions. They are;
• 1. Continental Shelf 2. Continental slope 3. Abyssal plains 4. The ocean deeps/ submarine trenches

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 120 to 370 meters from the surface water.
• ➢ Their width also varies from a few kilometers to more than 100 kilometers.
• ➢ This variation can be seen even in the context of the Indian peninsula. The continental shelf of the western coast of India is much wider than that of the eastern coast. (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. They are the sources of fishes, minerals including sand and gravel, etc.
• ➢ A large quantity of world’s petroleum and natural gas are obtained from the shelves.
• ➢ 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.
• ➢ These canyons are ‘steep-sided valleys’ cut into the floor of the seas. 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.

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