Maarg Manthan · Topic 10.5

The Indian Ocean

Geography › Ocean Relief, Oceans and Seas · Topic 10.5

The Indian Ocean is the third largest ocean, covering about 70.6 million square kilometres, and is the only major ocean named after a country. It is closed in the north by the Asian landmass, which makes its currents reverse with the monsoon. It has an inverted-Y ridge system, the Arabian Sea and the Bay of Bengal, key chokepoints, and a large share of the world's seaborne oil and container trade passes through it.

6 min read · UPSC Prelims · Geography · Ocean Relief, Oceans and Seas

At a Glance

Area About 70.6 million sq km
Named after India; the only such major ocean
Deepest point Java (Sunda) Trench, about 7,200 m
Key ridges Carlsberg, Central Indian, Ninety East
Peculiarity Monsoon reverses the surface currents
Exam link UPSC Prelims, Geography: Ocean Relief, Oceans and Seas

Where Does It Fit?

This is the fifth topic of the category on ocean relief, oceans and seas. The previous topic described the Atlantic, and this one covers the Indian Ocean, which is the ocean most important to India. The next topic describes the marginal seas of the world. Previous topic: The Atlantic Ocean. Next topic: Marginal Seas.

What Are the Extent and Special Features of the Indian Ocean?

In short: the Indian Ocean is a half-closed ocean, shut at the north by Asia, so its winds and currents follow the monsoon.

The Indian Ocean is bounded by Asia in the north, Africa in the west, Australia and the Sunda islands in the east, and the Southern Ocean in the south. It has an area of about 70.6 million square kilometres and an average depth of around 3,700 m. Unlike the Pacific and the Atlantic, it does not extend to the Arctic, because the Asian landmass closes it in the north at about 25 degrees north, and so it has no cold northern current and the northern part is warm. This leads to its biggest peculiarity: the surface currents in the north reverse direction with the monsoon winds, flowing clockwise in summer and anticlockwise in winter, as in Indian Ocean Currents. It is the warmest ocean and an important site of tropical cyclones and of the Indian Ocean Dipole, as in La Niña and El Niño Modoki.

What Are the Relief Features and Islands of the Indian Ocean?

Feature	Description
Mid-oceanic ridges	An inverted Y of ridges where plates diverge: the Carlsberg Ridge in the northwest, the Central Indian Ridge, the Southwest Indian Ridge and the Southeast Indian Ridge; they meet at the Rodrigues Triple Junction
Aseismic ridges	Ninety East Ridge, a straight ridge along 90 degrees east, and the Chagos-Laccadive Ridge, which carries the Lakshadweep, Maldives and Chagos atolls
Plateaus	Kerguelen Plateau in the south and the Mascarene Plateau
Trenches	Java (Sunda) Trench along Sumatra and Java, about 7,200 m, is the deepest; it was the origin of the 2004 tsunami, as in The 2004 Indian Ocean Tsunami and Warning Systems
Fans	The Bengal Fan, the largest submarine fan in the world, and the Indus Fan, built by the sediment of the Ganga-Brahmaputra and the Indus

The islands are of different origin. Madagascar, Sri Lanka and Socotra are continental fragments, the Andaman and Nicobar Islands are an island arc on the subduction zone, the Mascarenes, Mauritius and Réunion are volcanic, and the Maldives, Lakshadweep and the Chagos are coral atolls, as in Minor Ocean Relief Features. The Seychelles are granitic fragments of the old Gondwana. The Andaman and Nicobar Islands, with Indira Point at the southern tip of Great Nicobar, give India a long maritime reach toward the Malacca Strait.

What Are the Seas, Straits and Chokepoints?

Seas: the Arabian Sea, the Bay of Bengal, the Andaman Sea, the Laccadive Sea, the Red Sea, the Persian Gulf, the Gulf of Aden and the Gulf of Oman, as in Marginal Seas.
Strait of Hormuz: a narrow outlet of the Persian Gulf, through which roughly a fifth of the oil traded globally passes.
Bab-el-Mandeb: links the Red Sea with the Gulf of Aden and, through the Suez Canal, with the Mediterranean. Since late 2023, attacks on ships have forced many carriers to go around the Cape of Good Hope, and Suez traffic has remained below its earlier level in 2026, though container traffic has been returning gradually.
Strait of Malacca: between the Malay Peninsula and Sumatra, the shortest sea route between the Indian and Pacific oceans, and a vital route for China’s energy imports.
Mozambique Channel and the Cape route: the passage between Madagascar and Africa, and the route round the Cape of Good Hope for very large tankers.

Why Does the Indian Ocean Matter for India?

More than 90 per cent of India’s trade by volume moves by sea, and most of its oil imports arrive by Indian Ocean routes. The Indian Ocean Region has about one-third of the world’s population and a major share of world container and oil traffic. India has the Andaman and Nicobar Command and the Lakshadweep islands as forward bases, and works through the Indian Ocean Rim Association, IORA, which was formed in 1997, the vision of SAGAR, announced in 2015, and its successor MAHASAGAR, announced in 2025, with partners such as Mauritius, Sri Lanka and the Maldives. China’s growing presence in ports and naval activity, the American base at Diego Garcia and the competition around the Indo-Pacific give the region strategic importance. The ocean is also warming faster than the global average, with more marine heatwaves and intense Arabian Sea cyclones, and the Deep Ocean Mission of India aims to explore its resources. As an analytical point, India’s geography makes it the central power of the Indian Ocean, but the capacity of ports, navy and partnerships will decide whether it can turn the position into a lasting advantage.

Why Is This Topic Important?

Facts Ridges, islands and straits asked
Strategy IOR and chokepoints
Climate Monsoon and heating ocean

What Came Next?

The next topic describes the marginal seas of the world. Next topic: Marginal Seas.

Key People and Terms

Carlsberg Ridge Northwest Indian Ocean ridge
Ninety East Ridge Straight ridge along 90 degrees east
Java Trench Deepest part of the Indian Ocean
Bengal Fan Largest submarine fan
IORA Indian Ocean Rim Association
Chokepoint Narrow strategic sea passage

Exam Corner

Points to Remember

Only ocean named after a country.
Closed in the north, so the currents reverse with the monsoon.
The deepest part is the Java Trench.
Carlsberg Ridge is in the northwest.
Over 90 per cent of India’s trade volume goes by sea.

Do Not Confuse With

Ninety East Ridge and Carlsberg Ridge Aseismic versus spreading ridge
Hormuz and Malacca Persian Gulf outlet versus Indian-Pacific link
SAGAR and MAHASAGAR 2015 vision versus its 2025 successor

Memory Hook

Closed at the top, it turns with the monsoon; ridges form a Y, chokepoints guard the gates.

Mains Angle

Questions link the geography to strategy. These points add depth.

Peculiarity Monsoon reversal
Chokepoints Hormuz, Bab-el-Mandeb, Malacca
Policy SAGAR and MAHASAGAR

A Question You May Face

An original practice question, not a past paper question.

“Explain the physical peculiarities of the Indian Ocean and discuss its strategic importance for India.”

How to Answer

Physical Closed north, monsoon currents.
Relief Ridges and islands.
Chokepoints Straits.
Strategy IOR policies.

GS Relevance

Prelims: boundaries, ridges, islands, seas, straits, currents. GS Paper 1: oceans; GS Paper 2: India's maritime neighbourhood and strategy.

Frequently Asked Questions

Why is the Indian Ocean named after India?

The Indian Ocean has carried the name since ancient times, because the sea route across it linked India with the Middle East, Africa and Southeast Asia, and Indian merchants and sailors dominated the trade. It is the only major ocean named after a country.

What is the special feature of the Indian Ocean?

The Indian Ocean is closed in the north by the Asian landmass, so it lacks a northern polar connection, and its northern surface currents reverse direction with the monsoon winds. They flow clockwise in summer and anticlockwise in winter, unlike the permanent gyres in the Atlantic and the Pacific.

Which is the deepest part of the Indian Ocean?

The Java or Sunda Trench, south of Java and Sumatra in the Indonesian region, is the deepest part of the Indian Ocean, at about 7,200 to 7,300 metres. It lies along a subduction zone and generated the earthquake and tsunami of December 2004.

What is the Ninety East Ridge?

The Ninety East Ridge is a long, straight underwater ridge in the eastern Indian Ocean, running roughly along 90 degrees east longitude for about 5,000 kilometres. It is an aseismic ridge, formed by the movement of the Indian plate over a hotspot, not a spreading boundary.

Why is the Indian Ocean strategically important for India?

More than 90 per cent of India's trade by volume and most of its oil imports travel by sea across the Indian Ocean. Its chokepoints, such as Hormuz, Bab-el-Mandeb and Malacca, control energy supplies, so India works for a secure maritime region through IORA, SAGAR and MAHASAGAR.

PYQ Practice — Statement Analysis

1 The surface currents in the northern Indian Ocean reverse with the monsoon.

True

The ocean is closed in the north.

2 The Java Trench is the deepest part of the Atlantic Ocean.

False

It is the deepest part of the Indian Ocean.

3 The Chagos-Laccadive Ridge carries the Lakshadweep and Maldives atolls.