50 Fun Facts About Indian Ocean

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

Third largest, behind the Pacific and the Atlantic; unlike them it is landlocked to the north, so it never reaches Arctic waters.

What name is given to a severe tropical storm that forms over the Indian Ocean?

Cyclone: the very same storm is a hurricane in the Atlantic and a typhoon in the north-west Pacific, and only the location changes the name. A British official in India, Henry Piddington, coined the word in 1848.

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

The youngest: it only opened once the supercontinent Gondwana broke apart, and it grew in India's wake as that landmass drifted north-east.

Which traditional lateen-sailed vessel carried trade between Arabia, East Africa and India for centuries?

Dhow: for some two thousand years its crews rode the monsoon, sailing south to East Africa on the winter winds and home to Arabia once they reversed.

Ancient Greek sailors knew the Indian Ocean and its gulfs by which name, from their word for red?

Erythraean Sea: the label once covered the whole ocean, which is why a first-century Greek sailing manual bearing that name lists ports as far away as the Ganges.

Which East African language takes its name from the Arabic word for 'coasts'?

Swahili: it grew up as a trading tongue between Arab merchants and Bantu-speaking coast dwellers, which is why so much of its vocabulary is borrowed from Arabic.

Which hemisphere contains the entire Indian Ocean?

Eastern: every part of it lies east of the prime meridian, and its long undersea Ninety East Ridge is named for the 90°E line it follows, the middle of that hemisphere.

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

Tasmania: the line drops south from the island's South East Cape, so by the hydrographers' limits the whole Great Australian Bight counts as part of the Indian Ocean.

Which fish, the world's largest, gathers each year off Australia's Ningaloo Reef?

Whale shark: several hundred gather at Ningaloo each year to feed, yet for all their size they eat plankton, sieving it from the water through their gills.

Which pair of deep-sea trenches lies in the Indian Ocean?

Java and Makran: both mark places where the ocean floor is forced down beneath the Eurasian plate. The Java Trench, also called the Sunda Trench, holds the ocean's deepest point.

The 2009 hijacking of the cargo ship Maersk Alabama, later filmed as Captain Phillips, happened off which country's coast?

Somalia: pirates seized the ship some 440 km offshore and held Captain Richard Phillips in a lifeboat for days until US Navy snipers freed him. Tom Hanks played him in the 2013 film.

After disease wiped out Ceylon's coffee estates in the late 1800s, planters replanted the hills with which crop?

Tea: coffee rust took hold around 1870 and ruined the estates within a generation. The bushes planted in their place still sell under the old colonial name, Ceylon.

Which vast tidal forest covers the seaward edge of the Ganges-Brahmaputra delta?

Sundarbans: shared by India and Bangladesh, it is the world's largest mangrove forest, and the only one on Earth where tigers live.

Arab sailors timed their voyages by the monsoon, whose name comes from an Arabic word meaning what?

Season: mawsim meant the right time of year to sail. Portuguese crews picked the word up in these waters, and it passed into English, at least partly by way of Dutch.

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

Asia: each summer its vast landmass heats far faster than the sea and draws wet ocean air inland. In winter it cools and the winds turn to blow back out, reversing the ocean's currents with them.

India's summer monsoon is declared when its rains reach which south-western state, usually around 1 June?

Kerala: the rains reach its coast before anywhere else on the mainland, then sweep north over the following weeks, delivering most of India's yearly rainfall.

Which of these Indian Ocean waters has the saltiest surface?

Arabian Sea: far more water evaporates from it than rain and rivers return. Across India the Bay of Bengal is the reverse, freshened so heavily by the Ganges and other great rivers that it is the ocean's least salty corner.

What nickname do sailors give the westerly winds that sped Dutch ships across the southern Indian Ocean?

Roaring Forties: Dutch captains rode them east from the Cape before turning north for Java. Those who turned too late, like the Batavia in 1629, were wrecked on Australia's reefs.

The Bengal Fan, Earth's largest pile of seabed sediment, was worn off which mountain range?

Himalayas: India's collision with the landmass to its north pushed the range up, and ever since the Ganges and Brahmaputra have been carrying its debris out to sea.

Dugongs graze the Indian Ocean's seagrass shallows, and sailors' sightings of them are thought to have inspired tales of which creatures?

Mermaids: the link is written into science, because the dugong and its manatee cousins belong to an order named Sirenia, after the Sirens of Greek myth.

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

Coelacanth: the line was thought to have died out with the dinosaurs until museum curator Marjorie Courtenay-Latimer spotted one in a fishing crew's catch in 1938. The living genus, Latimeria, is named after her.

The 1883 eruption of which volcano was heard on Rodrigues, an island some 4,800 km away across the Indian Ocean?

Krakatoa: its final blast is reckoned the loudest sound in recorded history. Islanders that far off took it for the roar of distant guns, and the pressure wave was tracked right around the Earth.

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

Deccan Traps: the lava poured out around the time the dinosaurs died out, when India is thought to have drifted over the plume that now feeds Piton de la Fournaise on Réunion, one of the most active volcanoes on Earth.

The coco de mer palm, bearer of the largest seed in the plant kingdom, grows wild only in which island nation?

Seychelles: hollow nuts drifted across the ocean for centuries before anyone found the palm, so sailors decided they grew on trees beneath the waves, hence the name, 'coconut of the sea'.

Which Indian Ocean nation of 26 coral atolls has the lowest-lying terrain of any country on Earth?

Maldives: most of its islands stand less than a metre above the waves, so even a modest rise in sea level threatens the entire country.

Which island split from India some 88 million years ago, leaving its wildlife to evolve alone?

Madagascar: that long isolation is why about nine in ten of its plant and animal species, the lemurs among them, live nowhere else on Earth.

The first people to settle Madagascar were sailors who had crossed the ocean from where?

Indonesia: the closest relative of the Malagasy language is still spoken on Borneo, thousands of kilometres to the east, and the first settlers are thought to have crossed in outrigger canoes.

Every year millions of red crabs march from the forest to the sea to breed on which Australian island?

Christmas Island: the march begins with the first heavy rains late in the year and is timed by the phase of the moon. Roads are closed so the crabs can carpet the ground in safety.

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

Zheng He: his fleets sailed as far as East Africa and brought home a giraffe, which the Ming court hailed as a qilin, a mythical beast whose appearance signalled heaven's favour.

Vasco da Gama reached India in 1498 thanks to a pilot taken aboard at Malindi, a port in which modern country?

Kenya: Malindi's rulers were feuding with nearby Mombasa, which had just met the Portuguese with hostility, so they welcomed da Gama and found him a pilot who knew the monsoon winds to Calicut.

Which 14th-century Moroccan spent almost 30 years on the road, crossing the Indian Ocean to East Africa, India and China?

Ibn Battuta: he left Tangier in 1325 on a pilgrimage to Mecca and kept going for some 120,000 km. Along the way he served as a judge for the Sultan of Delhi, and once home he dictated it all in a book known as the Rihla.

Which island was the main market of the East African slave trade in the 19th century?

Zanzibar: Britain forced its sultan to shut the slave market in 1873, and an Anglican cathedral was raised on the site. Its altar is said to stand on the very spot of the old whipping post.

Britain's 1896 war with an East African sultanate is the shortest on record, having lasted roughly how long?

About 40 minutes: a new sultan took the throne without British approval and ignored an ultimatum to leave his palace. Royal Navy warships opened fire at 9 am, and before 10 the palace was ablaze and he had fled to the German consulate.

The Suez Canal's opening in 1869 gave steamships a short cut and ended the age of which fast sailing ships?

Clippers: steamships could take the new short cut while sail still had to round Africa, so the fast China ships lost their trade. Cutty Sark, launched the very year the canal opened, soon switched to hauling Australian wool.

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

Red Sea: the strait's Arabic name means 'Gate of Tears'. Since the Suez Canal opened, every ship taking that short cut between Europe and the East has had to squeeze through it.

Which strait between Sumatra and the Malay Peninsula is the main shipping lane linking the Indian Ocean with the Pacific?

Malacca Strait: it is the shortest sea route between India and China, so tankers carrying Gulf oil to the Far East crowd through it and past Singapore at its southern end, making it one of the busiest shipping lanes on Earth.

The Strait of Hormuz, the Persian Gulf's only sea exit, runs between Iran and an exclave of which country?

Oman: its Musandam Peninsula, cut off from the rest of the country by the United Arab Emirates, forms the strait's southern shore. Roughly a fifth of the world's oil is shipped past it.

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

Palk Strait: its waters are so shallow, and the sandbanks of Adam's Bridge so close to the surface, that big ships sailing between India's two coasts must take the long way round Sri Lanka.

By the hydrographers' limits, which sea lies between India's south-west coast, Sri Lanka and the atoll chains offshore?

Laccadive Sea: it takes in the Gulf of Mannar, whose oyster banks between India and Sri Lanka have been dived for pearls for some two thousand years.

Roughly how many people were killed by the 2004 Indian Ocean tsunami, the deadliest in recorded history?

About 230,000: the waves took only seven hours to cross the whole ocean, and they killed people on shores as far away as East Africa, thousands of kilometres from where they began.

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

Aceh: it suffered by far the worst of the disaster, and the shock helped end a separatist war that had dragged on there for almost 30 years. A peace deal was signed in Helsinki the following August.

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

Western Australia: satellite signals traced the jet far out over the ocean to the south-west of Perth. A piece of wing washed up on Réunion in 2015, but as of 2025 repeated deep-sea searches had not found the main wreck.

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

Bay of Bengal: North Sentinel is one of India's Andaman Islands, and landing there is against the law. When a helicopter flew over to check on the islanders after the 2004 tsunami, they fired arrows at it.

Which remote atoll in the Chagos Archipelago houses a major US military base, built after Britain removed the islanders?

Diego Garcia: the last plantation workers and their families were shipped off the atoll in the early 1970s to clear it for the base. American bombers later flew from it to strike Iraq and Afghanistan.

Which Indian Ocean island nation, where about two-thirds of the people have Indian roots, gained independence from Britain in 1968?

Mauritius: after slavery ended, planters shipped in indentured workers from India to cut sugar cane, and their descendants are now the majority. Long before anyone settled it, the island was the only home of the dodo.

Réunion saw the first official euro purchase in 2002 because it is part of which country?

France: Réunion is a full French department, and New Year reaches it hours before Europe, so the new notes and coins were legal there first. The first thing bought with them was a kilo of lychees.

Which cape, rather than the famous Cape of Good Hope, is Africa's true southern tip, where two oceans officially meet?

Cape Agulhas: its name is Portuguese for 'needles', perhaps for the jagged reefs that wrecked many ships, or because early sailors' compasses showed no deviation there. Its meridian officially divides the Atlantic from the Indian Ocean.

The remote Indian Ocean atoll of Aldabra is home to the world's largest population of which reptile?

Giant tortoises: more than 100,000 live on Aldabra, the last survivors of a kind once found on other Indian Ocean islands. The atoll is so remote, rugged and short of fresh water that people never settled it in numbers.

Which island off the Horn of Africa is famed for its umbrella-shaped dragon's blood trees?

Socotra: the trees bleed a dark red resin, the 'dragon's blood' of their name. They are far from the island's only oddity, because more than a third of its plant species grow nowhere else on Earth.

Which Indian spice did ancient Rome prize so highly that Alaric the Visigoth demanded 3,000 pounds of it as ransom?

Pepper: Roman ships rode the monsoon winds to India and came home loaded with it. The trade drained so much coin out of the empire that Pliny the Elder complained about the cost.