Islands

1. Distribution and geomorphological classification

An island is a landmass surrounded by water and smaller than a continent. India’s islands are best studied through both location and origin. The two major offshore archipelagos are Andaman and Nicobar in the southeastern Bay of Bengal and Lakshadweep in the southeastern Arabian Sea. Smaller islands occur along the mainland coast, within estuaries and lagoons, and in major rivers. They therefore cannot all be explained by a single process of formation.

The Andaman–Nicobar chain belongs to an active tectonic island-arc region, whereas Lakshadweep consists principally of coral formations developed over submerged volcanic foundations. Coastal islands may represent rocky outcrops, sediment accumulation, barrier formation or portions of coastal land separated by water. River islands develop through deposition and channel migration, particularly in large, sediment-rich rivers such as the Brahmaputra.

For map-based questions, relate islands to their surrounding water bodies, neighbouring countries and channels. The Andaman Sea lies east of the Andaman–Nicobar chain. Lakshadweep lies off India’s southwestern coast, while Sri Lanka is separated from southeastern India by the Palk Strait and Gulf of Mannar region. Avoid treating every offshore landmass as coral or every channel as an international boundary.

• Tectonic island-arc setting: Andaman and Nicobar Islands.
• Coral islands and atolls: Lakshadweep.
• Coastal and estuarine islands: Pamban, Diu, Sagar and Sriharikota.
• Riverine islands: Majuli and Umananda in the Brahmaputra.

2. Andaman and Nicobar Islands

The Andaman–Nicobar archipelago forms a roughly north–south chain between Myanmar and Sumatra. It is associated with the continuation of the Arakan Yoma–Andaman–Nicobar–Sumatra tectonic belt. Subduction of the Indian Plate beneath the Burma microplate, within the wider Sunda plate system, explains the region’s earthquakes, deformation and volcanism. The major islands are largely composed of folded sedimentary rocks and associated geological formations; it is incorrect to describe every island as a volcanic cone.

The Andaman group includes North, Middle and South Andaman, which together constitute Great Andaman, and Little Andaman farther south. Duncan Passage separates South Andaman and Little Andaman. The Ten Degree Channel separates Little Andaman from the Nicobar group. Important Nicobar islands include Car Nicobar, Nancowry, Katchal, Little Nicobar and Great Nicobar. Saddle Peak on North Andaman, about 732 metres high, is the highest point in the Union Territory.

Barren Island, east of the main Andaman chain, contains India’s only confirmed active volcano. Narcondam, farther northeast, is also volcanic. Great Nicobar contains Indira Point and the Galathea and Campbell Bay national parks. Rugged relief, heavy rainfall, tropical evergreen forests, mangroves and fringing reefs characterise much of the archipelago. Its small catchments support short streams rather than extensive mainland-style river systems.

• The Great Channel, also called the Six Degree Channel, lies between Great Nicobar and Sumatra.
• The Preparis Channel lies between Myanmar’s mainland and Preparis Island; it is not the channel separating Andaman and Nicobar.
• Port Blair was renamed Sri Vijaya Puram in September 2024.

3. Lakshadweep and coral-island formation

Lakshadweep is India’s smallest Union Territory by area, with approximately 32 square kilometres of land. Its official geographical description includes 36 islands, 12 atolls, three reefs and five submerged banks. These figures describe different geographical units and should not be added together as separate island totals. The islands lie on the northern part of the Lakshadweep–Maldives–Chagos ridge system and are generally low-lying, unlike the hilly Andaman and Nicobar Islands.

Coral polyps build calcium-carbonate skeletons that accumulate into reefs. Reef-building corals generally flourish in warm, shallow, clear, saline and well-lit tropical waters. Heavy sedimentation, freshwater influx and prolonged thermal stress can inhibit reef growth. An atoll is a ring-shaped or approximately ring-shaped reef enclosing a lagoon, sometimes carrying narrow sandy islands. Lakshadweep’s lagoons, reef flats and beaches reflect interactions among coral growth, waves, currents and sediment transport.

Darwin’s subsidence model explains a possible progression from a fringing reef around a volcanic island to a barrier reef and finally an atoll as the foundation sinks while coral growth continues upward. Actual reef histories also involve sea-level changes and erosion. Kavaratti is the administrative capital, while Minicoy lies separately to the south across the Nine Degree Channel. Low elevation, limited freshwater lenses and dependence on reefs make these islands particularly sensitive to erosion, saline intrusion and climate change.

• Lakshadweep was named the Laccadive, Minicoy and Amindivi Islands until 1973.
• Minicoy lies north of the Maldives, across the Eight Degree Channel.
• A lagoon is a shallow water body separated from the open sea by a reef, barrier or similar feature.

4. Coastal, lagoon and riverine islands

Coastal islands illustrate processes different from those of the two major archipelagos. Pamban, also called Rameswaram Island, lies off Tamil Nadu between the Palk Bay and Gulf of Mannar region. Adam’s Bridge is a chain of shoals between Pamban and Mannar Island in Sri Lanka. The Gulf of Mannar Marine National Park includes 21 islands and associated marine habitats, including coral reefs and seagrass beds.

Sriharikota is a barrier island in Andhra Pradesh between Pulicat Lake and the Bay of Bengal. It hosts the Satish Dhawan Space Centre. Sagar Island lies in the Hooghly estuarine region of West Bengal, while the wider Sundarbans contain numerous tidal islands shaped by sedimentation, erosion and shifting channels. Diu lies off Gujarat’s Kathiawar coast but belongs administratively to the Union Territory of Dadra and Nagar Haveli and Daman and Diu.

Majuli in Assam is a large inhabited river island within the Brahmaputra river system. Its changing banks demonstrate that river islands are dynamic depositional and erosional features rather than permanently fixed landforms. Umananda, near Guwahati, is a small rocky river island. Distinguish these from chars, which are often unstable sandbars or sedimentary islands. Statements about the world’s largest river island require caution because definitions and measured areas vary.

5. Ecological significance, hazards and strategic geography

India’s islands support coral reefs, mangroves, seagrass meadows and highly localised terrestrial species. Isolation promotes endemism: examples include the Narcondam hornbill and Nicobar megapode. Reefs reduce wave energy, mangroves stabilise shores, and seagrasses provide feeding grounds for dugongs. These habitats function together, so dredging, sediment discharge or coastal construction may affect ecological processes beyond the immediate project site.

Hazard exposure differs between island groups. Andaman and Nicobar face major earthquake and tsunami risks because of their tectonic setting. Lakshadweep is especially vulnerable to coastal flooding, wave action, freshwater scarcity and coral bleaching. Cyclones, invasive species, waste accumulation and excessive tourism can affect both groups. Management therefore requires carrying-capacity assessments, freshwater conservation, reef monitoring, early warning and construction suited to local coastal processes.

Strategically, Andaman and Nicobar overlook approaches to the Strait of Malacca, while Lakshadweep occupies an important position near Arabian Sea shipping routes. Island territories contribute to maritime entitlements under the United Nations Convention on the Law of the Sea, subject to its rules and boundary delimitation. Island Coastal Regulation Zone notifications provide the relevant coastal regulatory framework for these Union Territories. Conservation must also respect indigenous communities, including the Sentinelese, and restrictions under the Andaman and Nicobar Islands (Protection of Aboriginal Tribes) Regulation, 1956.

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