Maharashtra Board Class 11 Geography Chapter 7 Indian Ocean Relief and Strategic Importance PDF Download

Indian Ocean - Relief and Strategic Importance

Make Friends With Maps!

Look at figure 7.1 and answer the following questions:

1) What does this map show?

2) Which continents and sub-continents are visible in this map?

3) What lies between the continents?

4) Chagos Plateau, Sunda Trench, Central Mountain range are a part of what?

5) What are the conclusions you can draw after looking at the map?

Geographical Explanation

The Indian Ocean is the 3rd largest ocean in the world after Pacific and the Atlantic Ocean. It is the only ocean in the world named after a particular country i.e. India. About 20 percent of the total oceanic area is occupied by the Indian Ocean. A part of the Indian Ocean is located in the southern hemisphere. Indian Ocean spreads between Africa in the west, Asia in the north and east, Australia in the east, and Southern Ocean in the south. Look at figure 7.2 the areal extend of the oceans in given in the table. Note that unlike Pacific and Atlantic Ocean, the Indian Ocean does not extend northwards to the Arctic Ocean. This situation has resulted in complete blockage of the Indian Ocean towards its north. This peculiar arrangement of the ocean and the continental portion contributes a lot to the development of monsoon climate of the Indian subcontinent.

Teacher's Note

The Indian Ocean is very important for India because it is near our country. India's trade and oil supply depend on this ocean, just like how the Kerala coast has always been important for spice trade with Arab countries.

Exam Trick

Remember: Indian Ocean = only ocean named after a country = INDIA! Three continents touch it = Asia, Africa, Australia. Write this in your exam and you will get marks.

Points to Remember

Indian Ocean is the 3rd largest ocean in the world.
It is the only ocean named after a country.
About 20% of all ocean water is in the Indian Ocean.
It is blocked from the north and cannot reach the Arctic Ocean.
This blockage helps create monsoon winds over India.

Bottom Relief of Indian Ocean

The floor of Indian Ocean exhibits complex and varied features like continental shelf, mid-oceanic ridges, ocean basins, oceanic deeps, islands etc. These features are formed by tectonic, volcanic and denudation processes. These processes operate in the same manner as like that on the continents. The average depth of the Indian Ocean is 4000 m. It also has a few marginal seas.

Continental Shelf

It is a portion of continents, submerged under oceanic water. It is normally occupied by different gulfs, seas, bays and straits. There is a wide range of variation in the continental shelves of Indian Ocean. Quite extensive shelves are found along the Indian coasts. The Eastern coast of Africa and Madagascar record relatively narrow width of continental shelves and along the Indonesian coast, it is very narrow (160 km). The continental shelves are very wide in the west side of India whereas these are narrow along the eastern coast. Continental shelves are veneered with deposits brought down by terrestrial agents of erosion. Some of the sedimentary deposits, received over thousand years. As they remain deposited for a long time, sedimentary rocks are formed. Some of them are a potential source of fossil fuel.

Let's recall. Name the fossil fuels.

Teacher's Note

Continental shelf is like the beach area under water near a country's coast. In India, the western coast has a very wide shelf where sand and rocks collect, but the eastern coast has a narrow shelf.

Exam Trick

Remember: West India = Wide shelf. East India = Narrow shelf. Opposite of what you might think! Write this simple rule and remember it for your exam.

Points to Remember

Continental shelf is land that is underwater near the coast.
It is full of deposits from rivers and erosion.
West coast of India has wide shelves; east coast has narrow shelves.
Sedimentary rocks form here and can have fossil fuels.
The Indonesian coast has the narrowest shelf at only 160 km.

Mid-Oceanic Ridges

Mid oceanic ridges are submerged mountain ranges that separate deep portions of the sea (ocean) floor. In Indian Ocean also has a Mid Oceanic ridge called as a Mid Indian Oceanic ridge. It originates from Gulf of Eden near the Peninsula of Somalia. Further it extending toward the south and at east side of Madagascar it divided into two branches Among these, one branch diverts towards southwest and extends up to Prince Edward Island. It is known as Southwest Indian Ocean ridge. Second branch extends southeast up to Amsterdam and St. Paul Island. Mid Indian Oceanic ridge has many parallel ridges. This ridge is not continuous due to many fracture zones in it. Such as Owen fracture zone, Amsterdam fracture zone, etc.

A part from it in south Indian Ocean there is Kerguelen Plateau, in south side of Madagascar is Madagascar Plateau and in south side of Africa is Agulhas Plateau.

In the west of India in Indian Ocean lie a Chagos Plateau, which extends up to Mid Indian Ocean ridge. There are many archipelagos and islands in this part of Indian Ocean such as Lakshadweep, Maldives, Diego Garcia etc.

In the eastern Indian Ocean (Bay of Bengal) there is a long north-south extending range, called as Ninety East Ridge. It originates from the west of Andaman and Nicobar Island and extends south ward up to eastern part of Amsterdam and St. Paul Island.

Find out! Why Ninety East ridge name has been given to this ridge?

Teacher's Note

Mid-oceanic ridges are mountains under the ocean that you cannot see. The Mid Indian Oceanic ridge starts near Somalia and goes down toward the south, like a big underwater mountain range dividing the ocean floor.

Exam Trick

Remember: Mid Indian ridge = starts from Somalia = goes south = splits into 2 branches near Madagascar. One goes Southwest, one goes Southeast. Think of it like a Y-shape starting from the top.

Points to Remember

Mid Indian Oceanic ridge is an underwater mountain range.
It starts from the Gulf of Eden near Somalia.
It divides into two branches east of Madagascar.
Southwest branch goes to Prince Edward Island.
Southeast branch goes to Amsterdam and St. Paul Island.

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