Explain the Indian ocean with respect to following aspects:  Ocean Trenches , Abyssal Plains , ridges , Ocean Currents

(a) Ocean Trenches:

1. Trenches are the deepest portions in the oceans. 

2. There are very few deeps and trenches in the Indian Ocean as compared to other oceans. 

3. Most trenches of the Indian Ocean are located towards its eastern boundary. 

4. These are located along the converging boundaries of the Indo-Australian Plate and the Pacific Plate. 

5. The trenches in Indian Ocean are Java or Sunda Trench (7,450m deep) and Ob Trench (6,875m deep).

6. This area is seismically active because of plate movements.

(b) Abyssal Plains: 

1. Beyond the continental slope, lie the abyssal plains. They have a gentle slope and cover about 66 percent of the oceanic floor area. 

2. Abyssal plains of the ocean have deposits of polymetallic nodules. These nodules are a source of nickel, copper, manganese and cobalt. 

3. India has been allotted an area of 2 million square kilometres for research and excavation of polymetallic nodules by the International Seabed Authority in the Indian Ocean.

(c) Ridges: 

1. Mid Oceanic ridges are submerged mountain ranges that separate deep portions of the sea (ocean) floor. 

2. The Indian Ocean also Has a Mid Oceanic ridge called as a Mid Indian Oceanic ridge. 

3. It originates from the Gulf of Eden near the Peninsula of Somalia. 

4. Further it extends toward the south and on the East side of Madagascar, it gets 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. 

5. The second branch extends southeast up to Amsterdam and St. Paul Island.

6. 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.

(d) Ocean Currents:

1. The pattern of currents in the Indian Ocean differs from those in Pacific or Atlantic Oceans. 

2. The monsoon wind system has an effect on the currents in northern Indian Ocean. 

3. The shape of the coastline of the Indian Ocean, its extent, and the peculiar arrangement of the wind system that prevails in the region also influence the system of the ocean currents in the Indian Ocean. 

4. It has Equatorial Currents but the north equatorial current is weaker than the south equatorial current. 

5. North of the equator the currents are influenced by the seasonally reversing monsoon wind system. 

6. The current system in the southern part of the Indian Ocean leads to the development of a large gyre. 

7. South equatorial current flowing east to west direction under the influence of easterlies. The circulation is completed in the west by Mozambique – Agulhas currents. 

8. The second arm is ‘West Wind Drift’ flowing from west to east under the influence of westerlies and the circulation is completed in the east by West Australian current. It is considered to be one of the major gyres on global scale.

9. In the northern portion of the Indian Ocean seasonal monsoonal winds drive the current. During summer, they follow clockwise direction and during winter, their direction shows a complete reversal and they flow in anticlockwise direction.