50 Fun Facts About Indian Ocean

How does the Indian Ocean rank among the world's oceans by size?

It covers about 20% of the water on Earth's surface and is bounded by Asia, Africa and Australia.

Which ocean is the warmest in the world?

Its warm pool region heated by about 1.2 °C between 1901 and 2012, and models predict a near-permanent marine heatwave state by 2100.

Geologically, the Indian Ocean holds what distinction among the oceans?

It formed from the break-up of the Tethys Ocean, which split into the Mediterranean and the Indian Ocean only about 20 million years ago.

Before the Pacific was known, Western writers called the Indian Ocean by which directional name?

The Latin form Oceanus Orientalis Indicus is attested from 1515; Chinese sailors, coming the other way, called it the Western Oceans.

Ancient Greek geographers knew the Indian Ocean region by what name?

A first-century Alexandrian sailing guide, the Periplus of the Erythraean Sea, describes its ports and the monsoon winds.

The Sanskrit name Ratnakara for the Indian Ocean means what?

Traditional Indian geography also called it Mahodadhi, the big sea, split into a sunrise sea (Bay of Bengal) and a sunset sea (Arabian Sea).

Which hemisphere contains the entire Indian Ocean?

The centre of that hemisphere, the 90th meridian east, runs along the Ninety East Ridge.

The Indian Ocean's boundary with the Pacific runs south from a cape on which island?

The line follows the meridian of 146°49'E from South East Cape; the Atlantic boundary runs from Cape Agulhas.

What is the maximum depth of the Indian Ocean?

The low point lies in the Sunda (Java) Trench, one of only two trenches in the whole ocean.

Which two trenches are the only ones in the Indian Ocean?

The Java Trench runs 6,000 km; the Makran Trench, south of Iran and Pakistan, is just 900 km long.

Roughly how many people live in countries bordering the Indian Ocean?

That beats the Atlantic's 1.7 billion but trails the Pacific's 2.7 billion.

Which three countries have the longest Indian Ocean shorelines and exclusive economic zones?

Continental shelf makes up only 15% of the ocean, which has unusually narrow shelves.

The Ganges-Brahmaputra rivers flow into the world's largest delta, also known by what name?

It is also called the Sundarbans; the Bay of Bengal supplies more than half of all the runoff into the Indian Ocean.

The word 'monsoon' comes from an Arabic word meaning what?

Sailors used the seasonal winds long before the Greek Hippalus supposedly 'discovered' them in the first century.

Which continent drives the Indian Ocean monsoon, described as the strongest on Earth?

The seasonal wind shift even reverses the Somali Current and Indian Monsoon Current.

About what share of India's annual rainfall falls during the summer monsoon?

The region depends on it so heavily that civilisations perished when the monsoon failed.

Where is sea surface salinity highest in the Indian Ocean?

Evaporation beats rainfall there, pushing salinity above 36 PSU, while river runoff makes the Bay of Bengal the least salty at about 33 PSU.

The Indian Ocean garbage patch discovered in 2010 circulates the ocean roughly every how many years?

It rides the southern gyre from Australia to Africa, down the Mozambique Channel and back.

The Ganges and Indus submarine fans hold roughly what share of the ocean's sediment?

Both are built from material eroded off the Himalayas and carried down by the great rivers.

The Indian Ocean holds almost half of the world's what?

Mangroves originated in the region; Indonesia alone has half of the ocean's 80,984 square kilometres of them.

Which 'living fossil' fish, thought long extinct, was found alive off South Africa in the 1930s?

A second species turned up off Sulawesi in the late 1990s; most living specimens are known from the Comoros.

The Indian Ocean's three spreading ridges meet at a point named after which island?

There the Central Indian, Southwest Indian and Southeast Indian ridges divide the African, Indian, Antarctic and Australian plates.

The Réunion hotspot is linked to which enormous volcanic province in north-western India?

Its track runs from Réunion through the Mascarene Plateau and Chagos-Laccadive Ridge to the Indian mainland.

Which island group was the only one in the central Indian Ocean where an ancient civilisation flourished?

Unlike the Pacific, almost every Indian Ocean island stayed uninhabited until colonial times.

What is the average ground level of the world's lowest-lying country, 26 atolls south-west of India?

Its highest natural point is just 2.4 metres; the country's 26 atolls straddle the equator.

Roughly what share of Madagascar's wildlife is found nowhere else?

It split from Africa about 180 million years ago and from India about 90 million years ago, giving its lemurs and chameleons time to evolve alone.

The settlement of Madagascar around 1 CE was carried out by sailors from where?

The monsoon let ships sail west early in the season and return east a few months later.

The dodo was a flightless bird endemic to which Indian Ocean island?

Its closest living relative is the Nicobar pigeon; the Mare aux Songes swamp has yielded 250 of its bones per square metre.

Which Ming dynasty admiral led seven treasure voyages across the Indian Ocean between 1405 and 1433?

His fleets reached the coastal countries of East Africa and he called the ocean the Western Oceans.

Vasco da Gama reached India in 1498 with the help of a pilot given by a ruler in which Kenyan port?

The Portuguese kidnapped most of their other Swahili pilots in coastal raids.

Which Arab navigator compiled a guide to Indian Ocean navigation at the same time as Vasco da Gama?

Muslim geographers had mapped the ocean centuries before the Ottomans arrived in 1517.

Which island was the centre of the Indian Ocean slave trade in the 19th century?

As many as 50,000 slaves a year passed through its port in the mid-1800s.

Britain's 1896 war with an East African sultanate is history's shortest. Roughly how long did it last?

It broke out over the disputed succession of Sultan Khalid bin Barghash.

The Suez Canal, linking the Indian Ocean to the Mediterranean via the Red Sea, opened in which year?

It has no ship locks, which is why Red Sea species such as the goldband goatfish and swarms of jellyfish have invaded the Mediterranean.

The Bab-el-Mandeb strait connects the Gulf of Aden to which sea?

About 8% of the world's seaborne oil passes through it, against 40% through Hormuz and 35% through Malacca.

What share of the world's seaborne oil trade passes through the Indian Ocean and its chokepoints?

The Strait of Hormuz alone handles 40% of it, which is why the region's sea lanes rank among the most strategic anywhere.

Which country's waters lie on the far side of the Strait of Hormuz, the Persian Gulf's only sea exit?

The strait opens into the Gulf of Oman, and in 2023-2025 about a quarter of all seaborne oil passed through it.

Which waterway, together with the Gulf of Mannar and Adam's Bridge, separates Sri Lanka from India?

Until about 10,000 years ago a land bridge joined Sri Lanka to the subcontinent, which is why the two share so many species.

Which sea lies between the southern tip of India and the atolls to its south-west?

The Sea of Zanj lies far to the west, north of Madagascar.

The 2004 Indian Ocean tsunami on 26 December killed an estimated how many people?

The waves crossed the ocean at over 500 km/h and hit fourteen countries.

The 2004 earthquake that caused the tsunami had its epicentre off the coast of which Indonesian province?

At magnitude 9.2 to 9.3 it is the most powerful earthquake ever recorded in Asia.

Malaysia Airlines Flight 370 is thought to have crashed into the Indian Ocean off which coast?

The Boeing 777 with 239 people aboard vanished on 8 March 2014; the wreck has never been located.

The Sentinelese, called the most isolated people in the world, live on an island in which bay?

North Sentinel Island lies near South Andaman Island.

In 2025 the UK agreed to cede the Chagos Archipelago (Diego Garcia) to which country?

The International Court of Justice advised in 2019 that Britain must hand it over; a transfer treaty was signed in 2025.

Which Indian Ocean island nation, 70% of Indian descent, gained independence in March 1968?

It had been a key shipping node for the Dutch, French and British in turn.

Roughly what share of Earth's water surface does the Indian Ocean cover?

Its 70.56 million square kilometres include the Red Sea and Persian Gulf but exclude the Southern Ocean.

The Indian Ocean's boundary with the Atlantic runs south along 20°E from which South African headland?

The 20° east meridian marks the divide, while the Pacific boundary follows a meridian south from Tasmania.

What is the average depth of the Indian Ocean?

It was preceded by the Tethys Ocean, which broke into the Mediterranean and Indian Ocean only about 20 million years ago.

Which strait separates the island of Socotra from the Horn of Africa?

Socotra sits at the mouth of the Gulf of Aden, which the Bab-el-Mandeb links to the Red Sea.

Who was the first Greek recorded to have crossed the Indian Ocean, in the 2nd or 1st century BCE?

The possibly fictitious sailor Hippalus is credited with learning the direct monsoon route from Arabia to India around the same time.