Geography of the British Indian Ocean Territory

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The British Indian Ocean Territory prior to the Seychelles' independence in 1976. The land at bottom left is the northern tip of Madagascar. (Desroches is not labelled, but is a part of the Amirante Islands.)
Map of the British Indian Ocean Territory since 1976.

The British Indian Ocean Territory (BIOT) is an archipelago of 55 islands in the Indian Ocean South of India, it is situated approximately halfway between Africa and Indonesia. The islands form a semicircular group with an open sea towards the east. The largest, Diego Garcia, is located at the southern extreme end. It measures 60 square kilometres (23 sq mi) and accounts for almost three-quarters of the total land area of the territory.[1] Diego Garcia is the only inhabited island and is home to the joint UK-US naval support facility.[2][3] Other islands within the archipelago include Danger Island, Three Brothers, Nelsons Island, and Peros Banhos, as well as the island groups of the Egmont Islands, Eagle Islands, and Salomon Islands.[3]

Physical geography[edit]

BIOT is an archipelago of 55 islands.[4] They were annexed by the UK in 1965 under the Treaty of Paris from a much larger archipelago which in 1804 consisted of 2,300 independent islands.[2][3] BIOT is situated in the Indian Ocean near the Equator. It is roughly half-way between Africa and Indonesia, about 1,000 miles (1,600 km) southwest of India.[2][4] It is situated approximately 1,600 kilometres (990 mi) from South India and 600 kilometres (370 mi) to the south of the Maldives[5] With a coastline stretching 698 kilometres (434 mi), it is the southern extension of the Chagos-Laccadive Ridge.[6] The Chagos Islands archipelago are northeast of Mauritius, while Agalega Islands are due north.[7] The islands are characterised as coral atolls whose formation occurred at the summits of volcanic mountains these being submerged. The terrain is flat and low, with most areas not exceeding 2 metres (6 ft 7 in) above sea level.[4]

The climate is tropical marine; hot, humid, and moderated by trade winds. It is located outside the route of the cyclones.[3]

Marine reserve[edit]

The lagoon that surrounds the atoll has an area of about 120 square kilometres (46 sq mi). The maximum water depth in the lagoon is about 25 metres (82 ft). The width of the coral reef varies from 100–200 metres (330–660 ft) with a shallow depth of about 1 metre (3.3 ft) on the seaward side. The area covered by the fringing seaward reef shelf is about 35.2 square kilometres (13.6 sq mi). The bed slope noted at the outer edge of the reef shelf is steep towards the deeper end; the depth drops to more than 450 metres (1,480 ft) in some areas within 1 kilometre (0.62 mi) distance from the shore.

In 2010, the whole territory, as well as 545,000 square kilometres (210,426 sq mi) of ocean around the islands, was declared a marine reserve.[8] It is known formally as the Chagos Marine Protected Area,[9] because it is a "pristine ocean ecosystem now representing 16% of the world's fully protected coral reef."[10] Fishing is banned within the reserve area.[3] Diego Garcia is a Ramsar site.[11]


Of the 55 islands of the Chagos Archipelago, Diego Garcia is the largest. Aside from this, the main islands are the Egmont Islands, Danger Island, Eagle Islands, Three Brothers, Nelsons Island, Salomon Islands, and Peros Banhos at the northern end of the Chagos Archipelago.[12]

Left: Diego Garcia. Right: All of the unpaved roads present on the Diego Garcia island are made of white crushed coral.

The coral atoll of Diego Garcia is approximately 1,970 nautical miles (3,650 km) east of the coast of Africa (at Tanzania), 967 nautical miles (1,791 km) south-southwest of the southern tip of India (at Kanyakumari) and 2,550 nautical miles (4,720 km) west-northwest of the west coast of Australia (at Cape Range National Park, Western Australia). Diego Garcia lies at the southernmost tip of the Chagos-Laccadive Ridge — a vast submarine range in the Indian Ocean.[13] The total area encompassed by the atoll is 169.6 square kilometres (65.5 sq mi). At the entrance to the lagoon, there are three small islands, and these are East Island (7.49 hectares (18.5 acres)), Middle Island (4.98 hectares (12.3 acres)), and West Island (2 hectares (4.9 acres)).[14] In some areas, the atoll has both marshes and wetlands.[15] The ecosystem consists of undisturbed tropical forests.[16]

Île Boddam, with Île Diable in the background.

Egmont Atoll is also known as Six Isles and includes a seventh unnamed island. It was occupied for short periods during the mid 19th century[17] The atoll, in the form of “U”, is a small strip of land with width varying from 30 metres (98 ft) to a maximum of 3 kilometres (1.9 mi) at its northern extremity.. The total land area of the atoll is 2,430 hectares (6,000 acres). A fringing reef circumscribes the atoll. There are two openings into the ocean. It almost encompasses a large lagoon. The lagoon itself is 20 kilometres (12 mi) in length and is more than 10 kilometres (6.2 mi) in width. Rounded pumic stones found on the eastern beach of the island by one of the explorers of the island have been inferred as debris from the Krakatoa volcanic eruption of 1883 [18] The atoll is 23 leagues (111 km) to the northwest of Diego Garcia, on the Chagos Bank. The islands are connected by reefs which are steep and there are no locations for anchorage on its shores.[19]

Danger Island, a small coral patch which has shrubs and coconut trees is 5 leagues (24 km) from Six Islands. From the Danger islands, two of the Eagle Islands are 2 leagues (9.7 km) away. The Four Brothers are an island group 4 leagues (19 km) from Danger Island.[19] Danger Island is a 2 kilometres (1.2 mi) long and flat island with a maximum width of 400 metres (1,300 ft). It is covered with tall coconut trees. The closest land is Île Vache Marine, the southernmost of the Eagle Islands, which lies 16 kilometres (9.9 mi) to the north-northeast.[20]

Peros Benhos Islands, which are the largest group on the Chagos Bank, has a perimeter of 12 leagues (58 km). It consists of several groups of islets and reefs; deep channels separate them.[19]

Human geography[edit]

US personnel bringing survey equipment onto Diego Garcia, helped by Ilois, 1971.

In the late 18th century, coconut palm plantations were established on the island to produce copra for which slave labourers were brought in from Africa.[3][5] A small population lived in the archipelago, descendents of Mauritian laborers working the copra industry.[21] After an agreement was signed in 1966 between Britain and the United States, the US built a military base and forcibly evacuated all indigenous people; 1,200 from Diego Garcia, Ile du Coin, and Île Boddam were relocated to Mauritius,[22] while others went to the Seychelles. In 2000, the Chagos islanders won an appeal which restored their authority to live on the islands, and they received UK citizenship in the following year.[3] A 2008 court decision blocked their return. Further complications arose after the 2010 establishment of the world's largest marine reserve as the islanders' commercial fishing capabilities, if they returned to the archipelago, would be curtailed, thus hampering their traditional livelihood.[23]


  1. ^ Notholt 2008, p. 5.
  2. ^ a b c "British Indian Ocean Territory". Retrieved 23 June 2013. 
  3. ^ a b c d e f g "British Indian Ocean Territory". Encyclopedia Brittanica. Retrieved 23 June 2013. 
  4. ^ a b c Central Intelligence Agency 2010, p. 93.
  5. ^ a b Haggett 2001, p. 2627.
  6. ^ Green 2006, p. 408.
  7. ^ Paul 1987, p. 146.
  8. ^ "Blue Reef visitors win support for the Chago campaign". BBC. Retrieved 23 May 2013. 
  9. ^ "Chagos Island Marine Reserve". Marine Conservation Society (UK) SouthEast. Retrieved 23 June 2013. 
  10. ^ Acton 2012, p. 524.
  11. ^ "Diego García inscrito en la Lista de Ramsar / Diego Garcia, atoll de l'océan Indian, inscrit sur la liste de Ramsar" (in Spanish). Ramsar. 8 October 2001. Retrieved 1 July 2013. 
  12. ^ Vine 2011, p. 22.
  14. ^ Natural Resources Management Plan (2005), paragraph 2.5.1.
  15. ^ Natural Resources Management Plan (2005), paragraph
  16. ^ "Mauritius stakes claim for Chagos". BBC. 30 March 2004. Retrieved 23 June 2013. 
  17. ^ Evers & Kooy 2011, p. 27.
  18. ^ Paul 1987, p. 14.
  19. ^ a b c Tuckey 1815, pp. 64-65.
  20. ^ British Admiralty nautical chart 11000030 – 3 Chagos Archipelago, Scale 1:360,000
  21. ^ Dupont 2001, p. 1120.
  22. ^ Olson & Shadle 1991, p. 90.
  23. ^ Russell 2012, p. 269.


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