Indian Ocean | History, Map, Depth, Islands, & Facts

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data-icon="toc"></em> <a class="font-serif font-weight-bold text-black link-blue" href="https://www.britannica.com/place/Indian-Ocean">Indian Ocean</a> </div> <button aria-label="Close" class="js-sections-close-button btn-link btn-sm btn d-lg-none position-absolute top-0 p-10 right-0" > <em class="material-icons font-26" data-icon="close"></em> </button> </div> <div class="section-content pl-10 pr-20 pl-sm-50 pr-sm-60 pl-lg-5 pr-lg-10 pt-10 pt-lg-0 bg-gray-50 clear-catfish-ad"> <div class="toc mb-20"> <div class="font-serif font-14 font-weight-bold mx-15 mb-15 mt-20"> Table of Contents </div> <ul class="list-unstyled my-0" data-level="h1"><li data-target="#ref1"><div class="pl-25"><a class="link-gray-900 w-100" href="/place/Indian-Ocean">Introduction & Top Questions</a></div><div class="ml-40 toc-drawer sub-toc-drawer"></div></li><li data-target="#ref22755"><div class="d-flex align-items-center"><button class="h1-link-drawer-button btn btn-xs btn-circle d-flex rounded" type="button" aria-label="Toggle Heading"><em class="material-icons font-18" data-icon="keyboard_arrow_right"></em></button><a class="w-100 link-gray-900" href="/place/Indian-Ocean#ref22755">Physiography and geology</a></div><div class="ml-40 toc-drawer sub-toc-drawer"><ul class="list-unstyled" data-level="h2"><li data-target="#ref22756"><a class="w-100 link-gray-900" href="/place/Indian-Ocean#ref22756">Origin</a></li></ul><ul class="list-unstyled" data-level="h2"><li data-target="#ref22757"><a class="w-100 link-gray-900" href="/place/Indian-Ocean#ref22757">Submarine features</a><ul class="list-unstyled" data-level="h3"><li data-target="#ref22758"><a class="w-100 link-gray-900" href="/place/Indian-Ocean#ref22758">Oceanic ridges and fracture zones</a></li></ul><ul class="list-unstyled" data-level="h3"><li data-target="#ref22759"><a class="w-100 link-gray-900" href="/place/Indian-Ocean/Seamounts">Seamounts</a></li></ul><ul class="list-unstyled" data-level="h3"><li data-target="#ref22760"><a class="w-100 link-gray-900" href="/place/Indian-Ocean/Seamounts#ref22760">Ocean basins</a></li></ul><ul class="list-unstyled" data-level="h3"><li data-target="#ref22761"><a class="w-100 link-gray-900" href="/place/Indian-Ocean/Seamounts#ref22761">Continental rise, slope, and shelf</a></li></ul><ul class="list-unstyled" data-level="h3"><li data-target="#ref22762"><a class="w-100 link-gray-900" href="/place/Indian-Ocean/Seamounts#ref22762">Trenches</a></li></ul><ul class="list-unstyled" data-level="h3"><li data-target="#ref22763"><a class="w-100 link-gray-900" href="/place/Indian-Ocean/Bottom-deposits">Bottom deposits</a></li></ul></li></ul><ul class="list-unstyled" data-level="h2"><li data-target="#ref22764"><a class="w-100 link-gray-900" href="/place/Indian-Ocean/Bottom-deposits#ref22764">Surface features</a><ul class="list-unstyled" data-level="h3"><li data-target="#ref22765"><a class="w-100 link-gray-900" href="/place/Indian-Ocean/Bottom-deposits#ref22765">Coasts</a></li></ul><ul class="list-unstyled" data-level="h3"><li data-target="#ref22766"><a class="w-100 link-gray-900" href="/place/Indian-Ocean/Bottom-deposits#ref22766">Islands</a></li></ul></li></ul></div></li><li data-target="#ref22767"><div class="d-flex align-items-center"><button class="h1-link-drawer-button btn btn-xs btn-circle d-flex rounded" type="button" aria-label="Toggle Heading"><em class="material-icons font-18" data-icon="keyboard_arrow_right"></em></button><a class="w-100 link-gray-900" href="/place/Indian-Ocean/Bottom-deposits#ref22767">Climate</a></div><div class="ml-40 toc-drawer sub-toc-drawer"><ul class="list-unstyled" data-level="h2"><li data-target="#ref22768"><a class="w-100 link-gray-900" href="/place/Indian-Ocean/Bottom-deposits#ref22768">Monsoon zone</a></li></ul><ul class="list-unstyled" data-level="h2"><li data-target="#ref22769"><a class="w-100 link-gray-900" href="/place/Indian-Ocean/Trade-winds-zone">Trade-winds zone</a></li></ul><ul class="list-unstyled" data-level="h2"><li data-target="#ref22770"><a class="w-100 link-gray-900" href="/place/Indian-Ocean/Trade-winds-zone#ref22770">Subtropical and temperate zone</a></li></ul><ul class="list-unstyled" data-level="h2"><li data-target="#ref22771"><a class="w-100 link-gray-900" href="/place/Indian-Ocean/Trade-winds-zone#ref22771">Subantarctic and Antarctic zone</a></li></ul></div></li><li data-target="#ref22772"><div class="d-flex align-items-center"><button class="h1-link-drawer-button btn btn-xs btn-circle d-flex rounded" type="button" aria-label="Toggle Heading"><em class="material-icons font-18" data-icon="keyboard_arrow_right"></em></button><a class="w-100 link-gray-900" href="/place/Indian-Ocean/Trade-winds-zone#ref22772">Hydrology</a></div><div class="ml-40 toc-drawer sub-toc-drawer"><ul class="list-unstyled" data-level="h2"><li data-target="#ref22773"><a class="w-100 link-gray-900" href="/place/Indian-Ocean/Trade-winds-zone#ref22773">Surface currents</a></li></ul><ul class="list-unstyled" data-level="h2"><li data-target="#ref22774"><a class="w-100 link-gray-900" href="/place/Indian-Ocean/Trade-winds-zone#ref22774">Deep (thermohaline) circulation</a></li></ul><ul class="list-unstyled" data-level="h2"><li data-target="#ref22775"><a class="w-100 link-gray-900" href="/place/Indian-Ocean/Upwelling">Upwelling</a></li></ul><ul class="list-unstyled" data-level="h2"><li data-target="#ref22776"><a class="w-100 link-gray-900" href="/place/Indian-Ocean/Upwelling#ref22776">Surface temperatures</a></li></ul><ul class="list-unstyled" data-level="h2"><li data-target="#ref22777"><a class="w-100 link-gray-900" href="/place/Indian-Ocean/Upwelling#ref22777">Surface salinity</a></li></ul><ul class="list-unstyled" data-level="h2"><li data-target="#ref22778"><a class="w-100 link-gray-900" href="/place/Indian-Ocean/Upwelling#ref22778">Ice</a></li></ul><ul class="list-unstyled" data-level="h2"><li data-target="#ref22779"><a class="w-100 link-gray-900" href="/place/Indian-Ocean/Upwelling#ref22779">Tides</a></li></ul></div></li><li data-target="#ref22780"><div class="d-flex align-items-center"><button class="h1-link-drawer-button btn btn-xs btn-circle d-flex rounded" type="button" aria-label="Toggle Heading"><em class="material-icons font-18" data-icon="keyboard_arrow_right"></em></button><a class="w-100 link-gray-900" href="/place/Indian-Ocean/Economic-aspects">Economic aspects</a></div><div class="ml-40 toc-drawer sub-toc-drawer"><ul class="list-unstyled" data-level="h2"><li data-target="#ref22781"><a class="w-100 link-gray-900" href="/place/Indian-Ocean/Economic-aspects#ref22781">Mineral resources</a></li></ul><ul class="list-unstyled" data-level="h2"><li data-target="#ref22782"><a class="w-100 link-gray-900" href="/place/Indian-Ocean/Economic-aspects#ref22782">Biological resources</a></li></ul><ul class="list-unstyled" data-level="h2"><li data-target="#ref22783"><a class="w-100 link-gray-900" href="/place/Indian-Ocean/Economic-aspects#ref22783">Fisheries</a></li></ul><ul class="list-unstyled" data-level="h2"><li data-target="#ref22784"><a class="w-100 link-gray-900" href="/place/Indian-Ocean/Trade-and-transportation">Trade and transportation</a></li></ul><ul class="list-unstyled" data-level="h2"><li data-target="#ref332035"><a class="w-100 link-gray-900" href="/place/Indian-Ocean/Trade-and-transportation#ref332035">Tourism</a></li></ul><ul class="list-unstyled" data-level="h2"><li data-target="#ref22785"><a class="w-100 link-gray-900" href="/place/Indian-Ocean/Trade-and-transportation#ref22785">Environmental impact of human activity</a></li></ul></div></li><li data-target="#ref22786"><div class="d-flex align-items-center"><button class="h1-link-drawer-button btn btn-xs btn-circle d-flex rounded" type="button" aria-label="Toggle Heading"><em class="material-icons font-18" data-icon="keyboard_arrow_right"></em></button><a class="w-100 link-gray-900" href="/place/Indian-Ocean/Study-and-exploration">Study and exploration</a></div><div class="ml-40 toc-drawer sub-toc-drawer"><ul class="list-unstyled" data-level="h2"><li data-target="#ref22787"><a class="w-100 link-gray-900" href="/place/Indian-Ocean/Study-and-exploration#ref22787">Early exploration</a></li></ul><ul class="list-unstyled" data-level="h2"><li data-target="#ref22788"><a class="w-100 link-gray-900" href="/place/Indian-Ocean/Study-and-exploration#ref22788">Systematic investigations</a></li></ul></div></li></ul> <a class="toc-extra-link link-gray-900" href="https://www.britannica.com/place/Indian-Ocean/additional-info">References & Edit History</a> <a class="toc-extra-link link-gray-900" href="/facts/Indian-Ocean">Related Topics</a> </div> <div class="tlr-media-slider pb-10 mb-30"> <a class="section-header link-gray-900 font-serif font-14 font-weight-bold mb-10 mx-10" href="https://www.britannica.com/place/Indian-Ocean/images-videos">Images, Videos & Interactives</a> <div 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Lomonosov State University. Coauthor of <i>Reléf dna Indi&ihacek;skogo okeana </i>and others.</div> </a> <div data-popper-arrow></div> </div> <span class="btn btn-link editor-link p-0 qa-byline-link gtm-byline font-12 byline-contributor text-decoration-underline"> Viktor Filipovich Kanayev</span>, <div class="editor-popover popover p-0"> <a class="d-block p-20 gtm-byline font-12 byline-contributor" href="/contributor/Joseph-R-Morgan/3741" > <div class="editor-title font-16 font-weight-bold">Joseph R. Morgan</div> <div class="editor-description font-12 font-serif mt-5 clamp-description text-black">Associate Professor of Geography, University of Hawaii at Manoa, Honolulu. Coeditor of <i>Atlas for Marine Policy in Southeast Asian Seas.</i></div> </a> <div data-popper-arrow></div> </div> <span class="btn btn-link editor-link p-0 qa-byline-link gtm-byline font-12 byline-contributor text-decoration-underline"> Joseph R. 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They write new content and verify and edit content received from contributors.</div> </a> <div data-popper-arrow></div> </div> <span class="btn btn-link editor-link p-0 qa-byline-link font-12 "> The Editors of Encyclopaedia Britannica</span></div> <div class="last-updated font-12 font-serif"> <span class="text-gray-700"> Last Updated: <time datetime="2024-11-24T00:00:00CST" >Nov 24, 2024</time> •</span> <a class="byline-edit-history" href="https://www.britannica.com/place/Indian-Ocean/additional-info#history" rel="nofollow">Article History</a> </div></div> </div> <button class="d-flex d-lg-none btn btn-outline-blue border rounded-sm shadow-sm mobile-toc-button gtm-mobile-toc-inline-button d-none d-sm-block js-sections-inline-button module-spacing btn d-lg-none"> <em class="material-icons mr-5 ml-n10 my-n5 md-icon" data-icon="toc"></em> Table of Contents </button> <div class="d-flex d-sm-none flex-row"> <button class="d-flex d-lg-none btn btn-outline-blue border rounded-sm shadow-sm mobile-toc-button gtm-mobile-toc-inline-button js-sections-inline-button module-spacing"> <em class="material-icons mr-5 ml-n10 my-n5 md-icon" data-icon="toc"></em> Table of Contents </button> <button class="ai-ask-button btn border-2 ai-ask-button btn border-2 module-spacing btn-sm js-inline-ai-ask-button btn-outline-red-400 border-red-400 p-10 ml-5"> Ask the Chatbot a Question </button> </div> <script type="application/ld+json"> { "@context": "https://schema.org", "@type": "FAQPage", "mainEntity": [ { "@type" : "Question", "name" : "<div>What is the deepest point in the Indian Ocean?<\/div><em><\/em>", "acceptedAnswer" : { "@type" : "Answer", "text" : "The deepest point in the Indian Ocean, at 24,442 feet (7,450 meters), is in the Sunda Deep of the Java Trench off the southern coast of the island of Java (Indonesia)." } } , { "@type" : "Question", "name" : "<div>What surrounds the Indian Ocean?<\/div><em><\/em>", "acceptedAnswer" : { "@type" : "Answer", "text" : "The Indian Ocean is bounded by Iran, Pakistan, India, and Bangladesh to the north; the Malay Peninsula, the Sunda Islands, and Australia to the east; the Southern Ocean to the south; and Africa and the Arabian Peninsula to the west. In the southwest it joins the Atlantic Ocean, and to the east and southeast it mingles with the Pacific Ocean." } } , { "@type" : "Question", "name" : "<div>How big is the Indian Ocean?<\/div><em><\/em>", "acceptedAnswer" : { "@type" : "Answer", "text" : "The Indian Ocean, without its marginal seas, has an area of about 27,243,000 square miles (70,560,000 square km). The Indian Ocean\u2019s average depth is 12,274 feet (3,741 meters)." } } , { "@type" : "Question", "name" : "<div>What islands are found in the Indian Ocean?<\/div><em><\/em>", "acceptedAnswer" : { "@type" : "Answer", "text" : "The Indian Ocean has relatively few islands compared with the Atlantic and Pacific oceans. Madagascar, Maldives, Seychelles, Socotra, and Sri Lanka are continental fragments. The other islands include Christmas, Cocos, Farquhar, Prince Edward, Saint-Paul, Amsterdam, the Amirante, Andaman and Nicobar, Chagos, Crozet, Kerguelen, Sunda groups, Comoros, Lakshadweep, Mauritius, and R\u00E9union." } } , { "@type" : "Question", "name" : "<div>How old is the Indian Ocean?<\/div><em><\/em>", "acceptedAnswer" : { "@type" : "Answer", "text" : "The Indian Ocean is the smallest, geologically youngest, and physically most complex of the world\u2019s three major oceans (the others being the Pacific and Atlantic). Although it first opened some 140 million years ago, almost all of the Indian Ocean basin is less than 80 million years old. By 36 million years ago the Indian Ocean had taken on its present configuration." } } ] } </script> <div class="top-questions qa-accordion d-flex flex-column module-spacing"><div class="font-weight-bold font-14 mb-5"> Top Questions </div><div id="intent-accordion" class="md-intent-accordion"><div class="top-question bg-gray-50 rounded" data-value="1"><h3 class="accordion--question font-14 font-weight-normal cursor-pointer rounded"><div class="pe-none d-flex justify-content-between align-items-center"><div>What is the deepest point in the Indian Ocean?</div><em class="material-icons" data-icon="expand_more"></em></div></h3><div class="accordion--answer hidden p-15 pt-5 font-16 mb-5"><div class="accordion--answer-copy"><p>The deepest point in the Indian Ocean, at 24,442 feet (7,450 meters), is in the Sunda Deep of the Java Trench off the southern coast of the island of Java (Indonesia).</p></div></div></div><div class="top-question bg-gray-50 rounded" data-value="2"><h3 class="accordion--question font-14 font-weight-normal cursor-pointer rounded"><div class="pe-none d-flex justify-content-between align-items-center"><div>What surrounds the Indian Ocean?</div><em class="material-icons" data-icon="expand_more"></em></div></h3><div class="accordion--answer hidden p-15 pt-5 font-16 mb-5"><div class="accordion--answer-copy"><p>The Indian Ocean is bounded by Iran, Pakistan, India, and Bangladesh to the north; the Malay Peninsula, the Sunda Islands, and Australia to the east; the Southern Ocean to the south; and Africa and the Arabian Peninsula to the west. In the southwest it joins the Atlantic Ocean, and to the east and southeast it mingles with the Pacific Ocean.</p></div></div></div><div class="top-question bg-gray-50 rounded" data-value="3"><h3 class="accordion--question font-14 font-weight-normal cursor-pointer rounded"><div class="pe-none d-flex justify-content-between align-items-center"><div>How big is the Indian Ocean?</div><em class="material-icons" data-icon="expand_more"></em></div></h3><div class="accordion--answer hidden p-15 pt-5 font-16 mb-5"><div class="accordion--answer-copy"><p>The Indian Ocean, without its marginal seas, has an area of about 27,243,000 square miles (70,560,000 square km). The Indian Ocean’s average depth is 12,274 feet (3,741 meters).</p></div></div></div><div class="top-question bg-gray-50 rounded" data-value="4"><h3 class="accordion--question font-14 font-weight-normal cursor-pointer rounded"><div class="pe-none d-flex justify-content-between align-items-center"><div>What islands are found in the Indian Ocean?</div><em class="material-icons" data-icon="expand_more"></em></div></h3><div class="accordion--answer hidden p-15 pt-5 font-16 mb-5"><div class="accordion--answer-copy"><p>The Indian Ocean has relatively few islands compared with the Atlantic and Pacific oceans. Madagascar, Maldives, Seychelles, Socotra, and Sri Lanka are continental fragments. The other islands include Christmas, Cocos, Farquhar, Prince Edward, Saint-Paul, Amsterdam, the Amirante, Andaman and Nicobar, Chagos, Crozet, Kerguelen, Sunda groups, Comoros, Lakshadweep, Mauritius, and Réunion.</p></div></div></div><div class="top-question bg-gray-50 rounded" data-value="5"><h3 class="accordion--question font-14 font-weight-normal cursor-pointer rounded"><div class="pe-none d-flex justify-content-between align-items-center"><div>How old is the Indian Ocean?</div><em class="material-icons" data-icon="expand_more"></em></div></h3><div class="accordion--answer hidden p-15 pt-5 font-16 mb-5"><div class="accordion--answer-copy"><p>The Indian Ocean is the smallest, geologically youngest, and physically most complex of the world’s three major oceans (the others being the Pacific and Atlantic). Although it first opened some 140 million years ago, almost all of the Indian Ocean basin is less than 80 million years old. By 36 million years ago the Indian Ocean had taken on its present configuration.</p></div></div></div><button class="show-more-button js-toggle-top-questions btn btn-unstyled font-14 d-flex pr-10 rounded-sm"><em class="material-icons" data-icon="expand_more"></em></button></div></div><div class="bg-gray-50 p-15 rounded module-spacing recent-news d-flex flex-column float-false"> <div> <h2 class="font-weight-bold font-14 m-0 d-inline"> News <span class="text-gray-600">•</span> </h2> <div class="recent-news-item first-recent-news-item d-inline"> <a class="font-14 gtm-ap-news-link" href="/news/285876/e17204c33cb1fff12674eb261cbc6d18" rel="nofollow">Somalia says 24 people have died after 2 boats capsized in the Indian Ocean</a> <span class="font-14 text-gray-600"> <span>•</span> Nov. 24, 2024, 11:51 AM ET (AP) </span> </div> </div> <div class="rest-of-recent-news-items"> <button class="js-toggle-recent-news d-flex btn btn-unstyled font-14 pr-10 rounded-sm mt-10" aria-label="Toggle additional news items"> Show less <em class="material-icons" data-icon="expand_less"></em> </button> </div> </div><span class="marker before-article"></span><section data-level="1" id="ref1"><span class="marker PREMOD1 mod-inline"></span><p class="topic-paragraph"><strong><span id="ref150244"></span>Indian Ocean</strong>, body of <a href="https://www.britannica.com/science/seawater" class="md-crosslink autoxref " data-show-preview="true">salt water</a> covering approximately one-fifth of the total <a href="https://www.britannica.com/science/ocean" class="md-crosslink autoxref " data-show-preview="true">ocean</a> area of the world. It is the smallest, geologically youngest, and physically most complex of the world’s three major oceans (Pacific, Atlantic, and Indian). It stretches for more than 6,200 miles (10,000 km) between the southern tips of <a href="https://www.britannica.com/place/Africa" class="md-crosslink " data-show-preview="true">Africa</a> and <a href="https://www.britannica.com/place/Australia" class="md-crosslink " data-show-preview="true">Australia</a> and, without its <a class="md-dictionary-link md-dictionary-tt-off eb" data-term="marginal" href="https://www.britannica.com/dictionary/marginal" data-type="EB">marginal</a> seas, has an area of about 27,243,000 square miles (70,560,000 square km). The Indian Ocean’s average depth is 12,274 feet (3,741 metres), and its deepest point, in the Sunda Deep of the <a href="https://www.britannica.com/place/Java-Trench" class="md-crosslink " data-show-preview="true">Java Trench</a> off the southern coast of the island of <a href="https://www.britannica.com/place/Java-island-Indonesia" class="md-crosslink " data-show-preview="true">Java</a> (<a href="https://www.britannica.com/place/Indonesia" class="md-crosslink " data-show-preview="true">Indonesia</a>), is 24,442 feet (7,450 metres).</p><span class="marker MOD1 mod-inline"></span><span class="marker PREMOD2 mod-inline"></span><div class="assemblies"><div class="w-100"><figure class="md-assembly m-0 mb-md-0 card card-borderless print-false" data-assembly-id="95287" data-asm-type="image"><div class="md-assembly-wrapper card-media " data-type="image"><a href="https://cdn.britannica.com/11/83811-050-8A8D9F24/Island-resort-Maldives-Indian-Ocean.jpg" class="gtm-assembly-link position-relative d-flex align-items-center justify-content-center media-overlay-link card-media" data-href="/media/1/285876/95287"><picture><source media="(min-width: 680px)" srcset="https://cdn.britannica.com/11/83811-050-8A8D9F24/Island-resort-Maldives-Indian-Ocean.jpg?w=300"><img src="https://cdn.britannica.com/11/83811-050-8A8D9F24/Island-resort-Maldives-Indian-Ocean.jpg?w=300" alt="Maldives: island resort" data-width="1600" data-height="1105" loading="eager"></picture><button class="magnifying-glass btn btn-circle position-absolute shadow btn-white top-10 right-10" aria-label="Zoom in"><em class="material-icons link-blue" data-icon="zoom_in"></em></button></a></div><figcaption class="card-body"><div class="md-assembly-caption text-muted font-14 font-serif line-clamp"><span><a class="gtm-assembly-link md-assembly-title font-weight-bold d-inline font-sans-serif mr-5 media-overlay-link" href="https://cdn.britannica.com/11/83811-050-8A8D9F24/Island-resort-Maldives-Indian-Ocean.jpg" data-href="/media/1/285876/95287">Maldives: island resort</a><span>Island resort in the Maldives, north-central Indian Ocean.</span><button class="js-more-btn d-none btn btn-unstyled font-12 bg-white js-content" aria-label="Toggle more/less fact data"><span class="link-blue">(more)</span></button></span></div></figcaption></figure></div></div><p class="topic-paragraph">The Indian Ocean is bounded by <a href="https://www.britannica.com/place/Iran" class="md-crosslink " data-show-preview="true">Iran</a>, <a href="https://www.britannica.com/place/Pakistan" class="md-crosslink " data-show-preview="true">Pakistan</a>, <a href="https://www.britannica.com/place/India" class="md-crosslink " data-show-preview="true">India</a>, and <a href="https://www.britannica.com/place/Bangladesh" class="md-crosslink " data-show-preview="true">Bangladesh</a> to the north; the <a href="https://www.britannica.com/place/Malay-Peninsula" class="md-crosslink " data-show-preview="true">Malay Peninsula</a>, the <a href="https://www.britannica.com/place/Sunda-Islands" class="md-crosslink " data-show-preview="true">Sunda Islands</a> of Indonesia, and Australia to the east; the Southern Ocean to the south; and Africa and the <a href="https://www.britannica.com/place/Arabia-peninsula-Asia" class="md-crosslink " data-show-preview="true">Arabian Peninsula</a> to the west. In the southwest it joins the <a href="https://www.britannica.com/place/Atlantic-Ocean" class="md-crosslink " data-show-preview="true">Atlantic Ocean</a> south of the southern tip of Africa, and to the east and southeast its waters <a class="md-dictionary-link md-dictionary-tt-off eb" data-term="mingle" href="https://www.britannica.com/dictionary/mingle" data-type="EB">mingle</a> with those of the <a href="https://www.britannica.com/place/Pacific-Ocean" class="md-crosslink " data-show-preview="true">Pacific Ocean</a>.</p><span class="marker MOD2 mod-inline"></span><span class="marker PREMOD3 mod-inline"></span><div class="assemblies"><div class="w-100"><figure class="md-assembly m-0 mb-md-0 card card-borderless print-false" data-assembly-id="116892" data-asm-type="image"><div class="md-assembly-wrapper card-media " data-type="image"><a href="https://cdn.britannica.com/39/123239-050-20E493B4/lighthouse-Cape-Agulhas-South-Africa.jpg" class="gtm-assembly-link position-relative d-flex align-items-center justify-content-center media-overlay-link card-media" data-href="/media/1/285876/116892"><picture><source media="(min-width: 680px)" srcset="https://cdn.britannica.com/39/123239-050-20E493B4/lighthouse-Cape-Agulhas-South-Africa.jpg?w=300"><img src="https://cdn.britannica.com/39/123239-050-20E493B4/lighthouse-Cape-Agulhas-South-Africa.jpg?w=300" alt="Cape Agulhas" data-width="1600" data-height="1117" loading="eager"></picture><button class="magnifying-glass btn btn-circle position-absolute shadow btn-white top-10 right-10" aria-label="Zoom in"><em class="material-icons link-blue" data-icon="zoom_in"></em></button></a></div><figcaption class="card-body"><div class="md-assembly-caption text-muted font-14 font-serif line-clamp"><span><a class="gtm-assembly-link md-assembly-title font-weight-bold d-inline font-sans-serif mr-5 media-overlay-link" href="https://cdn.britannica.com/39/123239-050-20E493B4/lighthouse-Cape-Agulhas-South-Africa.jpg" data-href="/media/1/285876/116892">Cape Agulhas</a><span>The lighthouse at Cape Agulhas, South Africa.</span><button class="js-more-btn d-none btn btn-unstyled font-12 bg-white js-content" aria-label="Toggle more/less fact data"><span class="link-blue">(more)</span></button></span></div></figcaption></figure></div></div><p class="topic-paragraph">The question of defining the oceanic limits of the Indian Ocean is complicated and remains unsettled. The clearest border and the one most generally agreed upon is that with the Atlantic Ocean, which runs from <a href="https://www.britannica.com/place/Cape-Agulhas" class="md-crosslink " data-show-preview="true">Cape Agulhas</a>, at the southern tip of Africa, due south along the 20° E meridian. The border with the Pacific Ocean to the southeast is usually drawn from South East Cape on the island of <a href="https://www.britannica.com/place/Tasmania" class="md-crosslink " data-show-preview="true">Tasmania</a> south along the 147° E meridian. <a href="https://www.britannica.com/place/Bass-Strait" class="md-crosslink " data-show-preview="true">Bass Strait</a>, between Tasmania and Australia, is considered by some to be part of the Indian Ocean and by others to be part of the Pacific. The northeastern border is the most difficult to define. The one most generally agreed upon runs northwest from Cape Londonderry in Australia across the <a href="https://www.britannica.com/place/Timor-Sea" class="md-crosslink " data-show-preview="true">Timor Sea</a>, along the southern shores of the Lesser Sunda Islands and of <a href="https://www.britannica.com/place/Java-island-Indonesia" class="md-crosslink " data-show-preview="true">Java</a>, and then across the <a href="https://www.britannica.com/place/Sunda-Strait" class="md-crosslink " data-show-preview="true">Sunda Strait</a> to the shores of the island of <a href="https://www.britannica.com/place/Sumatra" class="md-crosslink " data-show-preview="true">Sumatra</a>. Between Sumatra and the Malay Peninsula the boundary is usually drawn across the <a href="https://www.britannica.com/place/Singapore-Strait" class="md-crosslink " data-show-preview="true">Singapore Strait</a>.</p><span class="marker MOD3 mod-inline"></span><div class="mb-20"><div class="w-100"><figure class="md-assembly m-0 mb-md-0 card card-borderless print-false" data-assembly-id="292926" data-asm-type="infogram"><div class="md-assembly-wrapper card-media " data-type="infogram"><script id="infogram_0__/KtQFEAQmy8fGJfHO5WRC" src="https://e.infogram.com/js/dist/embed.js?Itp" type="text/javascript" title="Dive deep into the depths of the ocean."></script></div></figure></div></div><span class="marker PREMOD5 mod-inline"></span><p class="topic-paragraph">There is no universal agreement on the southern limit of the Indian Ocean. In general (and for the purposes of this article), it is defined as extending southward to latitude 60° <a href="https://www.britannica.com/science/salinity" class="md-crosslink autoxref " data-show-preview="true">S</a>, based on the recognition by several researchers and other authorities of the presence of the <a href="https://www.britannica.com/place/Southern-Ocean" class="md-crosslink " data-show-preview="true">Southern Ocean</a> south of this line. Some authorities, however, maintain that the Indian Ocean extends to the Antarctic coast.</p><a class="link-module shadow-sm d-block qa-quiz-module" href="/quiz/everything-earth" data-link-module-iframe-link=""> <img loading="lazy" src="https://cdn.britannica.com/80/94580-131-EEFB2861/interior-Earth-layers-measurements-crust-mantle-core.jpg" alt="Cross section of Earth showing the core, mantle, and crust" class="rounded-sm mr-15" width="70" /> <div class="line-clamp clamp-5"> <div class="module-title bg-green">Britannica Quiz</div> <div class="font-weight-semi-bold mt-5">Everything Earth</div> </div> </a><span class="marker MOD5 mod-inline"></span><span class="marker PREMOD6 mod-inline"></span><div class="assemblies"><div class="w-100"><figure class="md-assembly m-0 mb-md-0 card card-borderless print-false" data-assembly-id="119032" data-asm-type="image"><div class="md-assembly-wrapper card-media " data-type="image"><a href="https://cdn.britannica.com/57/125057-004-1CA53C65/Great-Australian-Bight-Marine-Park-Australia.jpg" class="gtm-assembly-link position-relative d-flex align-items-center justify-content-center media-overlay-link card-media" data-href="/media/1/285876/119032"><picture><source media="(min-width: 680px)" srcset="https://cdn.britannica.com/57/125057-004-1CA53C65/Great-Australian-Bight-Marine-Park-Australia.jpg?w=300"><img src="https://cdn.britannica.com/57/125057-004-1CA53C65/Great-Australian-Bight-Marine-Park-Australia.jpg?w=300" alt="Great Australian Bight Marine Park" data-width="550" data-height="383" loading="eager"></picture><button class="magnifying-glass btn btn-circle position-absolute shadow btn-white top-10 right-10" aria-label="Zoom in"><em class="material-icons link-blue" data-icon="zoom_in"></em></button></a></div><figcaption class="card-body"><div class="md-assembly-caption text-muted font-14 font-serif line-clamp"><span><a class="gtm-assembly-link md-assembly-title font-weight-bold d-inline font-sans-serif mr-5 media-overlay-link" href="https://cdn.britannica.com/57/125057-004-1CA53C65/Great-Australian-Bight-Marine-Park-Australia.jpg" data-href="/media/1/285876/119032">Great Australian Bight Marine Park</a><span>Great Australian Bight Marine Park, southern Australia.</span><button class="js-more-btn d-none btn btn-unstyled font-12 bg-white js-content" aria-label="Toggle more/less fact data"><span class="link-blue">(more)</span></button></span></div></figcaption></figure></div></div><p class="topic-paragraph">The Indian Ocean has the fewest marginal seas of the major oceans. To the north are the inland <a href="https://www.britannica.com/place/Red-Sea" class="md-crosslink " data-show-preview="true">Red Sea</a> and <a href="https://www.britannica.com/place/Persian-Gulf" class="md-crosslink " data-show-preview="true">Persian Gulf</a>. The <a href="https://www.britannica.com/place/Arabian-Sea" class="md-crosslink " data-show-preview="true">Arabian Sea</a> is to the northwest, and the <a href="https://www.britannica.com/place/Andaman-Sea" class="md-crosslink " data-show-preview="true">Andaman Sea</a> to the northeast. The large gulfs of <a href="https://www.britannica.com/place/Gulf-of-Aden" class="md-crosslink " data-show-preview="true">Aden</a> and <a href="https://www.britannica.com/place/Gulf-of-Oman" class="md-crosslink " data-show-preview="true">Oman</a> are to the northwest, the <a href="https://www.britannica.com/place/Bay-of-Bengal" class="md-crosslink " data-show-preview="true">Bay of Bengal</a> is to the northeast, and the <a href="https://www.britannica.com/place/Great-Australian-Bight" class="md-crosslink " data-show-preview="true">Great Australian Bight</a> is off the southern coast of Australia.</p><span class="marker MOD6 mod-inline"></span><span class="marker PREMOD7 mod-inline"></span><p class="topic-paragraph">The Indian Ocean differs from the Atlantic and Pacific oceans in several other respects. In the Northern Hemisphere it is landlocked and does not extend to <a href="https://www.britannica.com/place/Arctic" class="md-crosslink autoxref " data-show-preview="true">Arctic</a> waters or have a temperate-to-cold zone. It has fewer islands and narrower continental shelves. It is the only ocean with an asymmetric and, in the north, semiannually reversing surface <a class="md-dictionary-link md-dictionary-tt-off eb" data-term="circulation" href="https://www.britannica.com/dictionary/circulation" data-type="EB">circulation</a>. It has no separate source of <a href="https://www.britannica.com/science/bottom-water" class="md-crosslink autoxref " data-show-preview="true">bottom water</a> (i.e., the Indian Ocean’s bottom <a href="https://www.britannica.com/science/water" class="md-crosslink autoxref " data-show-preview="true">water</a> originates outside its boundaries) and has two sources of highly saline water (the Persian Gulf and the Red Sea). Below the surface layers, especially in the north, the ocean’s water is extremely low in oxygen.</p><div class="module-spacing"> <DIV class="marketing-INLINE_SUBSCRIPTION marketing-content" data-marketing-id="INLINE_SUBSCRIPTION"><style> .student-promo-banner-wrapper { container-type: inline-size; margin-bottom: 15px; } @container (min-width: 475px) { .student-promo-banner { flex-direction: row; } .student-promo-banner-img-wrapper { margin-bottom: 0; margin-right: 10px; justify-content: flex-start; } .student-promo-banner-text-wrapper { text-align: left; margin-bottom: 0px; margin-left: 10px; } .student-promo-banner-button-wrapper { margin-right: 0; } }</style> <div class="student-promo-banner-wrapper"> <div class="student-promo-banner d-flex flex-column align-items-center bg-blue rounded p-20"> <div class="student-promo-banner-img-wrapper mb-20 mr-0 d-flex justify-content-center"> <img class="rounded" style="max-width: 100px; min-width: 80px" src="https://cdn.britannica.com/marketing/BlueThistle.webp" /> </div> <div class="student-promo-banner-text-wrapper ml-0 mb-10 text-center text-white"> <div class="h2 mb-10">Get Unlimited Access</div> <div class="h4 font-weight-semi-bold">Try Britannica Premium for free and discover more.</div> </div> <div class="student-promo-banner-button-wrapper d-flex justify-content-center align-items-center ml-auto mr-auto"> <a class="btn btn-m btn-orange" href="https://premium.britannica.com/premium-membership/?utm_source=premium&utm_medium=inline-cta&utm_campaign=black-friday-2024">Subscribe</a> </div> </div> </div> </DIV></div><span class="marker MOD7 mod-inline"></span></section> <span class="marker h2"></span><section data-level="1" id="ref22755"> <h2 class="h1">Physiography and geology</h2> <section data-level="2" id="ref22756"> <h2 class="h2">Origin</h2> <span class="marker PREMOD8 mod-inline"></span><div class="assemblies"><div class="w-100"><figure class="md-assembly m-0 mb-md-0 card card-borderless print-false" data-assembly-id="205047" data-asm-type="image"><div class="md-assembly-wrapper card-media " data-type="image"><a href="https://cdn.britannica.com/12/155312-050-A2EF0E56/Volcano-island-Reunion-Indian-Ocean.jpg" class="gtm-assembly-link position-relative d-flex align-items-center justify-content-center media-overlay-link card-media" data-href="/media/1/285876/205047"><picture><source media="(min-width: 680px)" srcset="https://cdn.britannica.com/12/155312-050-A2EF0E56/Volcano-island-Reunion-Indian-Ocean.jpg?w=300"><img src="https://cdn.britannica.com/12/155312-050-A2EF0E56/Volcano-island-Reunion-Indian-Ocean.jpg?w=300" alt="Réunion: volcano" data-width="1071" data-height="1600" loading="eager"></picture><button class="magnifying-glass btn btn-circle position-absolute shadow btn-white top-10 right-10" aria-label="Zoom in"><em class="material-icons link-blue" data-icon="zoom_in"></em></button></a></div><figcaption class="card-body"><div class="md-assembly-caption text-muted font-14 font-serif line-clamp"><span><a class="gtm-assembly-link md-assembly-title font-weight-bold d-inline font-sans-serif mr-5 media-overlay-link" href="https://cdn.britannica.com/12/155312-050-A2EF0E56/Volcano-island-Reunion-Indian-Ocean.jpg" data-href="/media/1/285876/205047">Réunion: volcano</a><span>Volcano erupting on the island of Réunion, western Indian Ocean.</span><button class="js-more-btn d-none btn btn-unstyled font-12 bg-white js-content" aria-label="Toggle more/less fact data"><span class="link-blue">(more)</span></button></span></div></figcaption></figure></div></div><p class="topic-paragraph">The origin and evolution of the Indian Ocean is the most complicated of the three major oceans. Its formation is a consequence of the breakup, which began about 180 million years ago, of the southern supercontinent <a href="https://www.britannica.com/place/Gondwana-supercontinent" class="md-crosslink " data-show-preview="true">Gondwana</a> (or Gondwanaland); by the movement to the northeast of the <a href="https://www.britannica.com/place/Indian-subcontinent" class="md-crosslink autoxref " data-show-preview="true">Indian subcontinent</a> (beginning about 125 million years ago), which began colliding with Eurasia about 50 million years ago; and by the western movement of Africa and separation of Australia from <a href="https://www.britannica.com/place/Antarctica" class="md-crosslink autoxref " data-show-preview="true">Antarctica</a> some 53 million years ago. By 36 million years ago the Indian Ocean had taken on its present <a class="md-dictionary-link md-dictionary-tt-off eb" data-term="configuration" href="https://www.britannica.com/dictionary/configuration" data-type="EB">configuration</a>. Although it first opened some 140 million years ago, almost all of the Indian Ocean basin is less than 80 million years old.</p><span class="marker MOD8 mod-inline"></span> </section> <section data-level="2" id="ref22757"> <h2 class="h2">Submarine features</h2> <section data-level="3" id="ref22758"> <h2 class="h3"><span id="ref150245"></span><a href="https://www.britannica.com/science/oceanic-ridge" class="md-crosslink " data-show-preview="true">Oceanic ridges</a> and fracture zones</h2> <span class="marker PREMOD9 mod-inline"></span><p class="topic-paragraph">The oceanic ridges consist of a rugged, seismically active mountain chain that is part of the worldwide oceanic ridge system and still contains centres of <span id="ref150246"></span><a href="https://www.britannica.com/science/seafloor-spreading" class="md-crosslink " data-show-preview="true">seafloor spreading</a> in several places. The ridges form an inverted Y on the ocean floor, starting in the upper northwest with the <a href="https://www.britannica.com/place/Carlsberg-Ridge" class="md-crosslink " data-show-preview="true">Carlsberg Ridge</a> in the Arabian Sea, turning due south past the Chagos-Laccadive Plateau, and becoming the <a href="https://www.britannica.com/place/Mid-Indian-Ridge" class="md-crosslink " data-show-preview="true">Mid-Indian (or Central Indian) Ridge</a>. Southeast of <a href="https://www.britannica.com/place/Madagascar" class="md-crosslink " data-show-preview="true">Madagascar</a> the ridge branches: the <a href="https://www.britannica.com/topic/Southwest-Indian" class="md-crosslink autoxref " data-show-preview="true">Southwest Indian</a> Ridge continues to the southwest until it merges into the Atlantic-Indian Ridge south of Africa, and the <a href="https://www.britannica.com/topic/Southeast-Indian" class="md-crosslink autoxref " data-show-preview="true">Southeast Indian</a> Ridge <a class="md-dictionary-link md-dictionary-tt-off eb" data-term="trends" href="https://www.britannica.com/dictionary/trends" data-type="EB">trends</a> to the east until it joins the Pacific-Antarctic Ridge south of Tasmania. Most striking is the <a href="https://www.britannica.com/science/aseismic-ridge" class="md-crosslink " data-show-preview="true">aseismic</a> (virtually earthquake-free) <span id="ref150247"></span><a href="https://www.britannica.com/place/Ninetyeast-Ridge" class="md-crosslink ">Ninetyeast Ridge</a>, which is the longest and straightest in the world ocean. First discovered in 1962, it runs northward along the 90° E meridian (hence its name) for 2,800 miles (4,500 km) from the zonal Broken Ridge at latitudes 31° S to 9° N and can be traced farther under the sediments of the Bay of Bengal. Other important meridional aseismic ridges include the Chagos-Laccadive, Madagascar, and <a href="https://www.britannica.com/place/Mozambique" class="md-crosslink autoxref " data-show-preview="true">Mozambique</a> plateaus, which are not part of the global oceanic ridge system.</p><div class="one-good-fact-module"> </div><span class="marker MOD9 mod-inline"></span> <span class="marker PREMOD10 mod-inline"></span><p class="topic-paragraph">The fracture zones of the Indian Ocean <a class="md-dictionary-link md-dictionary-tt-off eb" data-term="offset" href="https://www.britannica.com/dictionary/offset" data-type="EB">offset</a> the axis of the oceanic ridges mostly in a north-south direction. Prominent are the Owen, Prince Edward, Vema, and Amsterdam fracture zones along the ridges, with the immense Diamantina Fracture Zone found to the southwest of Australia.</p><span class="marker MOD10 mod-inline"></span> </section> </section></section><span class="marker end-of-content"></span><span class="marker after-article"></span></div> <div id="chatbot-root"></div> </div> </div> </div> <div class="ai-dialog-placeholder"></div> </div> </div> <aside class="col-md-da-320"></aside> </div> </div> </div> </div> </article></div> </div></div> </div> </main> <div id="md-footer"></div> <noscript><iframe src="//www.googletagmanager.com/ns.html?id=GTM-5W6NC8" height="0" width="0" style="display:none;visibility:hidden"></iframe></noscript> <script type="text/javascript" id="_informizely_script_tag"> var IzWidget = IzWidget || {}; (function (d) { var scriptElement = d.createElement('script'); scriptElement.type = 'text/javascript'; scriptElement.async = true; scriptElement.src = "https://insitez.blob.core.windows.net/site/f780f33e-a610-4ac2-af81-3eb184037547.js"; var node = d.getElementById('_informizely_script_tag'); node.parentNode.insertBefore(scriptElement, node); } )(document); </script>  <script> window.ap3c = window.ap3c || {}; var ap3c = window.ap3c; ap3c.cmd = ap3c.cmd || []; ap3c.cmd.push(function() { ap3c.init('ZO4siT4cLwnykPnzZWJtd3Byb2Q', 'https://engage.email.britannica.com/'); ap3c.track({v: 0}); }); ap3c.activity = function(act) { ap3c.act = (ap3c.act || []); ap3c.act.push(act); }; var s, t; s = document.createElement('script'); s.type = 'text/javascript'; s.src = "https://engage.email.britannica.com/app.js"; t = document.getElementsByTagName('script')[0]; t.parentNode.insertBefore(s, t); </script> <script class="marketing-page-info" type="application/json"> {"pageType":"Topic","templateName":"DESKTOP","pageNumber":1,"pagesTotal":8,"pageId":285876,"pageLength":1004,"initialLoad":true,"lastPageOfScroll":false} </script> <script class="marketing-content-info" type="application/json"> [] </script> <script src="https://cdn.britannica.com/mendel-resources/3-130/js/libs/jquery-3.5.0.min.js?v=3.130.14"></script> <script type="text/javascript" data-type="Init Mendel Code Splitting"> (function() { $.ajax({ dataType: 'script', cache: true, url: 'https://cdn.britannica.com/mendel-resources/3-130/dist/topic-page.js?v=3.130.14' }); })(); </script> <script class="analytics-metadata" type="application/json"> {"leg":"D","adLeg":"D","userType":"ANONYMOUS","pageType":"Topic","pageSubtype":null,"articleTemplateType":"PAGINATED","gisted":false,"pageNumber":1,"hasSummarizeButton":false,"hasAskButton":false} </script> <script type="text/javascript"> EBStat={accountId:-1,hostnameOverride:'webstats.eb.com',domain:'www.britannica.com', json:''}; </script> <script type="text/javascript"> ( function() { $.ajax( { dataType: 'script', cache: true, url: '//www.britannica.com/webstats/mendelstats.js?v=1' } ) .done( function() { try {writeStat(null,EBStat);} catch(err){} } ); })(); </script> <div id="bc-fixed-dialogue"></div> </body> </html>

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Indian Ocean | History, Map, Depth, Islands, & Facts | Britannica