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Andaman and Nicobar Islands

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Introduction

The Andaman and Nicobar Islands form a north-south arcuate archipelago in the Bay of Bengal, stretching approximately 750 km from near the Irrawaddy River delta of Myanmar in the north to the northern tip of Sumatra (Indonesia) in the south. The total land area is 8,249 square kilometers, comprising 572 islands, islets, and rocky outcrops — of which only 38 are permanently inhabited. Administered as a Union Territory of India, the archipelago serves as a crucial marker of India’s maritime boundaries and exclusive economic zone (EEZ) in the eastern Indian Ocean, while hosting unparalleled tropical biodiversity.

Geological Origin and Structure

The Andaman and Nicobar Islands are geologically classified as part of an island arc system — the Andaman-Sunda Arc — produced by the subduction of the Indo-Australian Plate beneath the Eurasian (Burma) Plate. The archipelago represents the emergent portions of the accretionary prism — deformed and uplifted deep-sea sediments scraped off the subducting plate — and the associated volcanic arc. The Andaman Sea to the east overlies the back-arc basin, formed by extensional tectonics behind the volcanic arc.

The two island groups are geographically and geologically distinct:

The Andaman Group: The northern cluster (latitude 10°N to 14°N) is separated from the Nicobar Group by the Ten Degree Channel (approximately 150 km wide and 400 fathoms deep). The Andamans are further subdivided into:

  • Great Andaman: The main island chain comprising North Andaman, Middle Andaman, and South Andaman (including Port Blair, the territorial capital near the southern tip), separated by narrow tidal channels.
  • Little Andaman: A smaller island south of Great Andaman, separated by the Duncan Passage.

The Andaman islands are underlain predominantly by folded and thrust-faulted sedimentary rocks — sandstones, shales, and limestone of Eocene to Miocene age — belonging to the Andaman Flysch and the Mithakhari Group. These rocks, originally deposited on the deep seafloor of the subducting Indian Plate, were scraped off, accreted to the overriding plate, and uplifted through continued tectonic compression. The islands continue to experience significant tectonic uplift at rates of 2-4 mm per year, with evidence from raised coral terraces and beach rock formations.

Ophiolite sequences — fragments of oceanic crust and upper mantle thrust onto continental crust — are exposed on several Andaman islands, particularly near Rutland Island and South Andaman. These ophiolites provide a rare opportunity to study fragments of actual oceanic lithosphere preserved on land.

The Nicobar Group: The southern cluster (latitude 6°N to 10°N) includes Car Nicobar (the administrative headquarters), Great Nicobar (the largest southern island of India), Katchal, Nancowry, Little Nicobar, and several smaller islands. The Nicobars are geologically younger, composed primarily of uplifted Tertiary and Quaternary reef limestones, marls, and calcareous sandstones. Great Nicobar marks the southernmost point of Indian territory — Indira Point (formerly Pygmalion Point, 6°45’N) — though this landform was significantly submerged by the 2004 Indian Ocean tsunami.

The 2004 Indian Ocean Tsunami

The Andaman and Nicobar archipelago was profoundly affected by the magnitude 9.1-9.3 Sumatra-Andaman earthquake on December 26, 2004. The earthquake resulted from rupture along the Sunda Trench subduction zone approximately 200 km east of the archipelago. The effects on the islands included:

  • Vertical displacement: The northern Andaman islands experienced subsidence of 1.0-1.5 meters, while the Nicobar Islands experienced uplift of up to 1.2 meters. This differential vertical movement flooded coastal villages and mangrove forests in the north while exposing new coral platforms in the south.
  • Tsunami devastation: Run-up heights reached 5-15 meters along the western coasts of the southern Nicobar Islands. The Nicobarese communities of Great Nicobar and Katchal sustained particularly severe losses.
  • Landscape change: Coral reefs were uplifted and killed by exposure in the Nicobars, while coastal morphology was dramatically altered across the archipelago.

Coral Reefs and Marine Ecosystems

The Andaman and Nicobar Islands possess some of India’s most extensive and biodiverse coral reef systems, covering approximately 2,000 square kilometers. The reef types include:

  • Fringing reefs: The most common type, extending directly from the shoreline around most islands.
  • Barrier reefs: Extending parallel to the coast, particularly well-developed on the western (seaward) side of the archipelago.
  • Atolls: Near-circular reefs enclosing central lagoons, exemplified by the Invisible Bank approximately 160 km southeast of Great Nicobar (though this lies outside territorial waters).

Coral diversity exceeds 200 scleractinian coral species, with post-2004 recovery showing encouraging resilience. The reefs support over 1,200 fish species, marine turtles (hawksbill, green, olive ridley, and leatherback), dugongs, dolphins, and whales. The Mahatma Gandhi Marine National Park near Wandoor on South Andaman protects representative reef ecosystems, while the Rani Jhansi Marine National Park in Ritchie’s Archipelago encompasses a cluster of islands and associated reefs.

Terrestrial Ecosystems

The islands’ tropical rainforest vegetation, classified as Andaman semi-evergreen, Andaman moist deciduous, and littoral forests, reflects the high annual rainfall (3,000-3,800 mm) and year-round warm temperatures. The forests exhibit high endemism — approximately 2,200 vascular plant species have been recorded, with roughly 15% endemic. Characteristic species include Andaman padauk (Pterocarpus dalbergioides — the state tree), Andaman bullet wood (Manilkara littoralis), and a diversity of orchids, ferns, and epiphytes.

Faunal endemism is equally remarkable. The islands host 26 endemic bird species including the Andaman wood pigeon, Andaman crake, Narcondam hornbill (restricted to the 6.8 square kilometer Narcondam Island — a dormant volcanic island), and the Nicobar megapode (a mound-nesting bird). Mammals include the Andaman wild pig, Andaman masked palm civet, and several endemic bat and rodent species. Notably, the Andamans have no large native terrestrial predators.

Indigenous Communities

The Andaman Islands are home to six indigenous tribes classified as Particularly Vulnerable Tribal Groups (PVTGs):

  • Great Andamanese: Formerly the dominant tribe comprising ten sub-groups, now reduced to fewer than 60 individuals, resettled on Strait Island.
  • Onge: Approximately 100-120 individuals on Little Andaman Island.
  • Jarawa: Approximately 400-500 individuals in the western reserve forest of South and Middle Andaman, living in voluntary isolation with some managed contact.
  • Sentinelese: The most isolated human population on Earth, residing on North Sentinel Island (approximately 60 square kilometers), estimated at 50-100 individuals who violently repel all external contact.
  • Shompen and Nicobarese: The Nicobar tribe, with the Nicobarese (approximately 30,000, the only non-PVTG tribe in the islands) and the Shompen (approximately 250, semi-nomadic hunter-gatherers in the interior of Great Nicobar).

These communities represent some of the earliest human migrations out of Africa, with the Andamanese tribes having inhabited the islands for an estimated 26,000-60,000 years.