Islands and the Indian Ocean map

Detail

1. What an island is, and the largest islands

• Island: a piece of land with water all around it. It is smaller than a continent. Australia is counted as a continent, so Greenland is the world's largest island (NCERT, Class 6).
• Archipelago: a group or chain of islands, for example Lakshadweep, Maldives and Chagos.
• India has about 1,300 islands (NCERT, Class 6). The two main groups are Andaman and Nicobar in the Bay of Bengal and Lakshadweep in the Arabian Sea.

Rank	Island	Ocean or sea	Country or countries
1	Greenland	North Atlantic and Arctic	Denmark (self-governing territory)
2	New Guinea	Western Pacific	Indonesia (west) and Papua New Guinea (east)
3	Borneo	South China Sea and Java Sea	Indonesia (Kalimantan), Malaysia (Sabah, Sarawak), Brunei
4	Madagascar	South-west Indian Ocean	Madagascar
5	Baffin	Arctic	Canada
6	Sumatra	Indian Ocean	Indonesia
7	Honshu	North-west Pacific	Japan (its main island)
8	Great Britain	North Atlantic	United Kingdom

• Borneo is the only island shared by three countries. Indonesia is building its new capital, Nusantara, in East Kalimantan on Borneo. It will replace Jakarta, which is on Java.

2. Madagascar: the "Indian Ocean island that left India"

• Location: off south-east Africa in the south-west Indian Ocean. The Mozambique Channel, about 400 km wide, separates it from the African mainland [8].
• How it formed, step by step:
• Gondwana, the old southern supercontinent, broke into pieces.
• Madagascar and India first split away from Africa as one block.
• About 88 million years ago, India broke away from Madagascar and drifted north-east until it hit Asia. Madagascar stayed where it was.

• Result: Madagascar has been an isolated island for tens of millions of years.

• Endemism means a species is found naturally in only one place in the world.

• Long isolation let Madagascar's wildlife evolve on its own. Most of its plants and animals are endemic.

• Lemurs are primates found only on Madagascar. The island has about 40 species of lemur [8][9].

• Why it matters: Madagascar is a textbook example of continental drift (the slow movement of continents over time) and of island biodiversity hotspots, which are places with many endemic species that are also under threat.

3. Divided and disputed islands

Type	Island	Who is involved	Where
Divided (one island, two or more countries)	Hispaniola	Haiti (west), Dominican Republic (east)	Caribbean Sea
Divided	Timor	Timor-Leste (east), Indonesia (west)	Between the Indian and Pacific Oceans
Divided	Ireland	Republic of Ireland, Northern Ireland (UK)	North Atlantic
Divided	Cyprus	Republic of Cyprus (south), Turkish-held north	Eastern Mediterranean
Divided	Borneo, New Guinea	See the table above	South-east Asia
Disputed (ownership claimed by more than one country)	Kuril Islands	Russia and Japan ("Northern Territories" to Japan)	Between Hokkaido and Kamchatka, north-west Pacific
Disputed	Senkaku / Diaoyu	Japan and China (Taiwan also claims them)	East China Sea
Disputed	Falklands / Malvinas	UK and Argentina	South-west Atlantic
Disputed (now being settled)	Chagos	UK and Mauritius	Central Indian Ocean (see section 7)

4. Hotspot and "science" islands

• Hotspot: a fixed, very hot plume of magma deep in the mantle. As a plate moves over it, the plume pushes up a line of volcanoes.

Island group	Ocean	How it formed	Why it is famous
Hawaii (USA)	Central Pacific	Hotspot in the middle of the Pacific plate. The plate moves over it, so the islands get older towards the north-west	Shield volcanoes such as Mauna Loa and Kilauea
Galapagos (Ecuador)	Eastern Pacific, on the equator	Hotspot volcanoes	Endemic species. They helped Darwin form the theory of natural selection
Iceland	North Atlantic	Sits on the Mid-Atlantic Ridge, a divergent boundary (where two plates move apart), plus a hotspot	Rift valleys, geysers, geothermal energy. The ridge rises above sea level here

5. The Indian Ocean island chain (read west to east)

Group	Islands	Who owns them	Where
Island countries	Madagascar, Comoros, Seychelles, Mauritius, Maldives, Sri Lanka	Independent	Mauritius and Seychelles are in the south-west. The Maldives are south-west of India. Sri Lanka is south of Tamil Nadu
French territories	Reunion (next to Mauritius), Mayotte (in the Comoros group), Kerguelen (southern Indian Ocean, near the Antarctic)	France	Give France a large maritime zone in the Indian Ocean
Australian territories	Cocos (Keeling), Christmas Island	Australia	Eastern Indian Ocean, south-west of Indonesia
Yemeni	Socotra	Yemen	Near the mouth of the Gulf of Aden, a key shipping lane to the Red Sea
Indian	Andaman and Nicobar (Bay of Bengal), Lakshadweep (Arabian Sea)	India	A and N lie close to the Strait of Malacca. Lakshadweep lies on the main shipping lanes across the Arabian Sea
Disputed / transferred	Chagos (including Diego Garcia)	UK to Mauritius (2025 treaty)	Central Indian Ocean

• Channels to remember (NCERT, Class 9 and 11):
• Ten Degree Channel separates the Andaman Islands from the Nicobar Islands.
• Nine Degree Channel separates the main Lakshadweep islands from Minicoy.
• Eight Degree Channel separates Minicoy from the Maldives.

• Palk Strait separates India from Sri Lanka.

• How the islands differ:

• Lakshadweep and the Maldives are coral islands: atolls (ring-shaped coral reefs around a lagoon).
• Andaman and Nicobar are the tops of a drowned mountain range that continues the Arakan Yoma. Barren Island, India's only active volcano, is part of this chain.
• Mauritius and Reunion are volcanic, formed by the Reunion hotspot.
• Madagascar and Sri Lanka are pieces of continent (old Gondwana land).

6. Agalega Islands

• Location: two small islands of Mauritius (North and South Agalega) in the western Indian Ocean, about 1,100 km north of the main island of Mauritius.
• India's project:
• On 29 February 2024, PM Narendra Modi and Mauritian PM Pravind Jugnauth jointly opened, by video conference, a new airstrip, the St. James Jetty and six community development projects [2][3].

• India paid for the whole project. It fulfilled a promise PM Modi made to the people of Agalega in 2015 [2][3].

• Why it matters:

• Connectivity: better links between mainland Mauritius and far-off Agalega [2].
• Maritime security: better maritime surveillance, which means watching ships and activity at sea, over the western Indian Ocean. This helps against piracy, illegal fishing and smuggling [2].
• Development: helps local people earn a living and improves services [2].

7. Chagos Archipelago

• Location: central Indian Ocean, south of the Maldives. Its largest island is Diego Garcia, which has a US-UK military base.
• Timeline:

Year	Event
1965	Britain separated Chagos from colonial Mauritius and called it the "British Indian Ocean Territory"
1968	Mauritius became independent, but without Chagos. Islanders (Chagossians) were later moved out
25 Feb 2019	ICJ advisory opinion: Mauritius's decolonisation was not lawfully completed in 1968. The UK must end its rule over Chagos "as rapidly as possible". All UN members must help finish the decolonisation [4]
22 May 2019	UNGA resolution 73/295 welcomed the opinion. It said Chagos is an integral part of Mauritius and asked the UK to withdraw within six months. The vote was 116 for, 6 against (Australia, Hungary, Israel, Maldives, UK, USA) and 56 abstentions [4][5]
2025	UK-Mauritius treaty gives sovereignty (legal ownership) of Chagos to Mauritius. The UK keeps the Diego Garcia base on a 99-year lease. Check the latest ratification status

• ICJ advisory opinion: a legal opinion from the International Court of Justice, given when a UN body asks for one. It is not legally binding, but it carries great moral and legal weight.
• India's stand: India supported Mauritius. It voted for resolution 73/295, in line with its long support for decolonisation.

8. India's policy frame: from SAGAR to MAHASAGAR

• SAGAR (2015): "Security and Growth for All in the Region". It was announced in Mauritius in 2015. India would act as a net security provider (a country that helps keep its neighbours' seas safe) and a development partner in the Indian Ocean.
• MAHASAGAR (March 2025): "Mutual and Holistic Advancement for Security and Growth Across Regions". PM Modi launched it during his visit to Mauritius in March 2025 [6][7].
• It covers trade for development, capacity building for sustainable growth and mutual security for a shared future [7].
• India works through technology sharing, concessional loans (low-interest loans) and grants [7].

• It reaches beyond the Indian Ocean to the wider Global South, through education, health, housing, scholarships and skill projects [7].

• India-Mauritius: ties were raised to an "Enhanced Strategic Partnership" in March 2025 [6].

• Ports as strategic nodes (Hambantota, Gwadar, Chabahar) are covered in the india-neighbours note.

Prelims Hooks

• Largest islands in order: Greenland > New Guinea > Borneo > Madagascar > Baffin > Sumatra > Honshu > Great Britain.
• Borneo is shared by three countries: Indonesia (Kalimantan, where the new capital Nusantara is), Malaysia (Sabah, Sarawak) and Brunei.
• Madagascar is separated from Africa by the Mozambique Channel. It split from India about 88 million years ago. Lemurs are endemic to it.
• Reunion, Mayotte and Kerguelen belong to France. Cocos (Keeling) and Christmas Island belong to Australia. Socotra belongs to Yemen.
• Trap: Agalega belongs to Mauritius, not Seychelles. It received an India-funded airstrip and St. James Jetty, opened on 29 February 2024 [2].
• Diego Garcia is in the Chagos Archipelago. The ICJ advisory opinion came on 25 February 2019. UNGA resolution 73/295 passed 116–6 with 56 abstentions [4][5].
• Which countries voted against 73/295? UK, USA, Australia, Hungary, Israel and the Maldives [4].
• MAHASAGAR stands for Mutual and Holistic Advancement for Security and Growth Across Regions. It was launched in Mauritius, March 2025 [6][7]. SAGAR dates from 2015.
• Channels, north to south: Ten Degree (Andaman–Nicobar) → Nine Degree (Lakshadweep–Minicoy) → Eight Degree (Minicoy–Maldives).
• Iceland sits on the Mid-Atlantic Ridge, a divergent boundary. Hawaii and Galapagos are hotspot islands.

Mains Points

• Islands give India strategic depth (GS-III, GS-II):
• Andaman and Nicobar watch over the Strait of Malacca. Lakshadweep sits on the Arabian Sea sea lanes.
• Partner islands extend India's reach into the western Indian Ocean. Examples are Agalega (airstrip and jetty, 2024) and Mauritius and Seychelles more widely.

• This helps maritime surveillance, HADR (Humanitarian Assistance and Disaster Relief) and responses to piracy and to a growing Chinese presence.

• Decolonisation and international law (GS-II):

• The Chagos case runs from the 1965 separation to the ICJ opinion (2019), then UNGA 73/295 and finally the 2025 treaty.
• It shows how advisory opinions and UN votes can build pressure for a negotiated settlement.

• India's support for Mauritius fits its anti-colonial position and builds trust with small island states.

• Island biogeography and conservation (GS-I, GS-III):

• Long isolation leads to high endemism, as in Madagascar's lemurs, the Galapagos and Hawaii.
• The same isolation makes island species vulnerable to habitat loss, invasive species and climate change.

• Low-lying coral atolls, such as the Maldives and Lakshadweep, face sea-level rise.

• Policy response (GS-II, GS-III): India moved from SAGAR (2015) to MAHASAGAR (2025) [6][7]. It now pairs security with development: trade, capacity building, concessional finance and community projects in island states.