The Andaman & Nicobar Islands

The Andaman & Nicobar Islands are a group of 572 islands, islets, and rocks, spread over from Cape Negrais in Burma (North) to Achin Head in Sumatra (South) fro about 780 km. It width is nowhere more than 32 miles. It forms the archipelago named Andaman & Nicobar covering an area of 8249 sq km. It is believed to have evolved as a result of subduction of Indian plate below the Southeast Asian plate.

It is an Union Territory of India, and is located in the long trade route of India, Burma (now Myanmar), and the Far East in the sea; and between India and Thailand and other South East countries on the air route.

The islands, with the exception of Narcondam Island, form almost like an arc within a parallelogram located between 6° and 14° of the North Latitude and between 92° and 94° of East Longitude.

These are sometimes called "the Islands of the Marigold Sun". These are situated mostly in the Bay of Bengal from North to South as a garland from Land Fall Island in the extreme North to the Great Nicobar Island in the extreme South, and has no land connection with the mainland India. The archipelago is also inhabited by aborigines - Negrito in Andaman and Mongoloid in Nicobar.

It is here the southernmost point of India is located in the Campbell bay in the Great Nicobar Island, which is known as Indira Point, approaching Indonesia. The northernmost point is located adjacent to Myanmar. Located in the midst of the Andaman Sea, the archipelago is situated within the close quarters of the some South East Asian countries like Indonesia, Thailand, Jawa, Sumatra, and Malaysia.

The 10 degree furious channel divides the archipelago in two different identical regions. The northern part is called Andaman, and the southern part is called Nicobar. The word Andaman is most likely derived from a Malay word 'Handuman' used by Malay pirates and trader of Andamanese people in ancient times to refer to the people of the land. The term Nicobar, many scholars believe, seems a corrupt derivation of 'Nakkavaram', a south Indian term meaning 'a land of naked people.

The islands, islets, and the rocks form an accurate chain running from Myanmar in the north to Indonesia in the south along Indo-Sumatra subduction zone. To the east of the chain are situated the volcanic islands called the Narcondam and Barren Islands.

The Andamans has rugged hilly terrain with north to south trending ridges separated by narrow elongated valleys. There are hill ranges, plains and swamps. Isolated hills and hill slopes are also there. In the eastern part of the islands, there are several peaks of 200-300 metre heights. The highest peak is the Saddle peak situated in the North Andaman. Its height is 732 metre from the mean seal level. The hill slopes are moderate to steep, and are susceptible to heavy soil erosion. Flat lands are few which are mainly in the Betapur and Diglipur villages. Kalpong River is the main river of the North Andaman that originates from Saddle peak. The main rivers of the Middle Andaman are Betapur and Rangat rivers, and of South Andaman is Dhanikhari.

Hill ranges and hills in the Nicobars are very few. It has flat to undulatory terrains. Its northernmost island is Car Nicobar having an area of 129 sq km. It is almost flat except for its central part having highest elevation of about 69 metre. The elevated areas are gently undulating. The ridges are low and linear and trending from North to Northwest or from South to Southwest. The Island shelf is relatively steep in the east and west compared to the north and south. The island is surrounded by coral reefs on all sides which get submerged during high tides. Between the coral reefs and the mainland, there are sandy beaches of width varying from 5 to 50 metre. Water bodies flowing to the south mostly converse in an extensive mangrove swamps north of Kimois village.

The topography of the almost elliptical Great Nicobar island is highly undulating and immature. Coastal plains and swamps are common. The highest peak of this island in Mt Thullier. Its height is 642 metre above mean sea level. It is located in the north-central part of the island. There are many peaks above the height of 200 metre. The hill ranges trend from North to South. Embayments are formed all around such as Campbell Bay and South Bay in the east and Mata Tanuwa and Nanjappa Bay in the west. The island is surrounded by coral reefs. There is a road in the East-West direction passing through the hilly terrain which at a point attains a maximum height of 180 metre from the mean sea level. In the south of this road the relief falls gradually and the topography becomes almost flat near Pygmalion Point and west of Galathea Bay. The eastern and western coastlines of this Island are highly irregular and deeply incised. The central part of the island is a watershed.

The metaphoric rocks found in Andaman and Nicobar Islands include quartzite, quartzsericite schist, phyllite, amphiobolite etc which are formed in Precambrian Age extending from about 4.6 billion years ago (the point at which Earth began to form) to the beginning of the Cambrian Period, 541 million years ago. The ophiolites, the oceanic crust, belongs to Cretaceous Age (100-80 million years ago). These include ultramafic rocks, mafic rocks like gabbros, basalts etc, plagiogranite, diorite, dolerite, and some sedimentaries, chert, limestone, and shale. The sedimentary rocks are of younger age formed between Eocene Age (56 to 33.9 million years ago) and Pliocene Age (5.3 to 2.5 million years ago). These rocks are composed of lithopackages of conglomerate, sandstone, siltstone, shale, limestone etc.

The Andaman and Nicobar Islands fall under a very high damage risk seismic zone named Zone V.

There is a different geomorpho-tectonic setup in the Andaman Sea in the east. The seabed has a complex topography indicating its volcanic system and the backarc spreading ridge. There are several seamount near the volcanic region with heights ranging from 500 to 2000 metre. South of the volcanic Islands lies invisible bank having 170x50 sq km area with a flat top. The multi-peaked Alcock and Sewell seamounts are located in the eastern part of the sea. Irrawaddy river in the northeastern part of the sea has made the bottom topography smooth with rapid sediment deposition. There is a narrow valley of about 1000 metre deep. There is also an isolated rift valley in the northeast. The Nicobar Rift Valley is located in the southwest.

In the west of the Islands the sediments are mostly biogenic having a depth range of 30-230 metre and thereafter up to 4,300 metre. The sediments are pelagic ooze.

The island has a tropical climate. No extreme summer or winter is felt. Minimum temperature in February hovers round 23°C and maximum 32.5°C in November. Humidity is relatively high. Enjoyable sea wind blows all the time. The Islands are exposed to both the Southwest (May-October) and Northeast (November-December) monsoons. During 2001-2011, rainfall ranged between 3114.6mm to 3771.64 mm annually.