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50 free Indian Ocean trivia questions with answers — geography quiz, new questions added Aug 2026.
The Indian Ocean is the ocean people crossed first. Its calm waters and reversing monsoon winds let Gujarati merchants, Roman sailors and Indonesian settlers of Madagascar trade and travel across it thousands of years before anyone dared the Atlantic, which is why historians call it the 'first global economy'. This quiz covers that story: the Periplus of the Erythraean Sea, Zheng He's treasure fleets, Vasco da Gama's Swahili pilots, the Dutch and British East India companies, the Suez Canal and the 38-minute Anglo-Zanzibar War. It also covers the ocean itself: why it is the warmest and geologically youngest, its two trenches, its hotspot ridges, the Bengal and Indus fans, the garbage patch that circles it every six years, and the coelacanth that turned up alive off South Africa. Then it visits the islands: Madagascar's endemic wildlife, the low-lying Maldives, Mauritius and its dodo, Diego Garcia and Zanzibar. It ends with the 2004 tsunami, MH370 and the sea lanes carrying most of the world's oil. Every answer was checked against Wikipedia's articles on the Indian Ocean and its features, and each question shows the sentence that supports it. Try our Atlantic Ocean, Pacific Ocean and Arctic Ocean quizzes next.
30 of 50 questions with answers and explanations. Play the quiz
Q 01How does the Indian Ocean rank among the world's oceans by size?
Third largest
It covers about 20% of the water on Earth's surface and is bounded by Asia, Africa and Australia.
Q 02Which ocean is the warmest in the world?
Indian
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.
Q 03Geologically, the Indian Ocean holds what distinction among the oceans?
The youngest
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.
Q 04Before the Pacific was known, Western writers called the Indian Ocean by which directional name?
Eastern
The Latin form Oceanus Orientalis Indicus is attested from 1515; Chinese sailors, coming the other way, called it the Western Oceans.
Q 05Ancient Greek geographers knew the Indian Ocean region by what name?
Erythraean Sea
A first-century Alexandrian sailing guide, the Periplus of the Erythraean Sea, describes its ports and the monsoon winds.
Q 06The Sanskrit name Ratnakara for the Indian Ocean means what?
Mine of jewels
Traditional Indian geography also called it Mahodadhi, the big sea, split into a sunrise sea (Bay of Bengal) and a sunset sea (Arabian Sea).
Q 07Which hemisphere contains the entire Indian Ocean?
Eastern
The centre of that hemisphere, the 90th meridian east, runs along the Ninety East Ridge.
Q 08The Indian Ocean's boundary with the Pacific runs south from a cape on which island?
Tasmania
The line follows the meridian of 146°49'E from South East Cape; the Atlantic boundary runs from Cape Agulhas.
Q 09What is the maximum depth of the Indian Ocean?
7,290 m
The low point lies in the Sunda (Java) Trench, one of only two trenches in the whole ocean.
Q 10Which two trenches are the only ones in the Indian Ocean?
Java and Makran
The Java Trench runs 6,000 km; the Makran Trench, south of Iran and Pakistan, is just 900 km long.
Q 11Roughly how many people live in countries bordering the Indian Ocean?
More than two billion
That beats the Atlantic's 1.7 billion but trails the Pacific's 2.7 billion.
Q 12Which three countries have the longest Indian Ocean shorelines and exclusive economic zones?
Australia, Indonesia and India
Continental shelf makes up only 15% of the ocean, which has unusually narrow shelves.
Q 13The Ganges-Brahmaputra rivers flow into the world's largest delta, also known by what name?
Sundarbans
It is also called the Sundarbans; the Bay of Bengal supplies more than half of all the runoff into the Indian Ocean.
Q 21Which 'living fossil' fish, thought long extinct, was found alive off South Africa in the 1930s?
Coelacanth
A second species turned up off Sulawesi in the late 1990s; most living specimens are known from the Comoros.
Q 22The Indian Ocean's three spreading ridges meet at a point named after which island?
Rodrigues
There the Central Indian, Southwest Indian and Southeast Indian ridges divide the African, Indian, Antarctic and Australian plates.
Q 23The Réunion hotspot is linked to which enormous volcanic province in north-western India?
Deccan Traps
Its track runs from Réunion through the Mascarene Plateau and Chagos-Laccadive Ridge to the Indian mainland.
Q 14The word 'monsoon' comes from an Arabic word meaning what?
Season
Sailors used the seasonal winds long before the Greek Hippalus supposedly 'discovered' them in the first century.
Q 15Which continent drives the Indian Ocean monsoon, described as the strongest on Earth?
Asia
The seasonal wind shift even reverses the Somali Current and Indian Monsoon Current.
Q 16About what share of India's annual rainfall falls during the summer monsoon?
80%
The region depends on it so heavily that civilisations perished when the monsoon failed.
Q 17Where is sea surface salinity highest in the Indian Ocean?
Arabian Sea
Evaporation beats rainfall there, pushing salinity above 36 PSU, while river runoff makes the Bay of Bengal the least salty at about 33 PSU.
Q 18The Indian Ocean garbage patch discovered in 2010 circulates the ocean roughly every how many years?
Six
It rides the southern gyre from Australia to Africa, down the Mozambique Channel and back.
Q 19The Ganges and Indus submarine fans hold roughly what share of the ocean's sediment?
40%
Both are built from material eroded off the Himalayas and carried down by the great rivers.
Q 20The Indian Ocean holds almost half of the world's what?
Mangrove habitat
Mangroves originated in the region; Indonesia alone has half of the ocean's 80,984 square kilometres of them.
Q 24Which island group was the only one in the central Indian Ocean where an ancient civilisation flourished?
Maldives
Unlike the Pacific, almost every Indian Ocean island stayed uninhabited until colonial times.
Q 25What is the average ground level of the world's lowest-lying country, 26 atolls south-west of India?
1.5 metres
Its highest natural point is just 2.4 metres; the country's 26 atolls straddle the equator.
Q 26Roughly what share of Madagascar's wildlife is found nowhere else?
Over 90%
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.
Q 27The settlement of Madagascar around 1 CE was carried out by sailors from where?
Indonesia
The monsoon let ships sail west early in the season and return east a few months later.
Q 28The dodo was a flightless bird endemic to which Indian Ocean island?
Mauritius
Its closest living relative is the Nicobar pigeon; the Mare aux Songes swamp has yielded 250 of its bones per square metre.
Q 29Which Ming dynasty admiral led seven treasure voyages across the Indian Ocean between 1405 and 1433?
Zheng He
His fleets reached the coastal countries of East Africa and he called the ocean the Western Oceans.
Q 30Vasco da Gama reached India in 1498 with the help of a pilot given by a ruler in which Kenyan port?
Malindi
The Portuguese kidnapped most of their other Swahili pilots in coastal raids.