Chagos Archipelago
The Chagos Archipelago or Chagos Islands is a group of seven atolls comprising more than 60 islands in the Indian Ocean about south of the Maldives archipelago. This chain of islands is the southernmost archipelago of the Chagos–Laccadive Ridge, a long submarine mountain range in the Indian Ocean. In its north are the Salomon Islands, Nelsons Island and Peros Banhos; towards its south-west are the Three Brothers, Eagle Islands, Egmont Islands and Danger Island; southeast of these is Diego Garcia, by far the largest island. All are low-lying atolls, save for a few extremely small instances, set around lagoons.
The islands were first permanently settled by Europeans. From 1715 to 1810, the Chagos Islands were part of France's Indian Ocean possessions, administered through Isle de Francewhich was a colony of France. Under the Treaty of Paris in 1814, France ceded and the Chagos Islands to the United Kingdom.
In 1965, the United Kingdom split its administration of the Chagos Archipelago away from Mauritius and into the British Indian Ocean Territory. The islands were formally established as an overseas territory of the United Kingdom on 8 November 1965.
The Chagos Islands had been home to the Chagossians, a Bourbonnais Creole–speaking people, until the United Kingdom expelled them from the archipelago at the request of the United States between 1967 and 1973 to allow the United States to build Naval Support Facility Diego Garcia, which operates under a special agreement allowing significant US military presence. The main forcible removal of Diego Garcia's population took place in July and September 1971. Since 1971 only the atoll of Diego Garcia has been inhabited, and only by employees of the military, including civilian contracted personnel. Since being expelled, the Chagossians have been prevented from re-entering the islands.
Mauritius engaged in a sovereignty dispute with the UK, claiming the Chagos Archipelago as part of Mauritius. The International Court of Justice in 2019 and the International Tribunal for the Law of the Sea both stated that the UK had an obligation to return the islands to Mauritius. In October 2024, the British government announced it would transfer the Chagos Islands to Mauritius subject to finalisation of a treaty. The transfer agreement was signed on 22 May 2025, with the provision that the island of Diego Garcia would be leased back to the UK for at least 99 years. The UK government expected the treaty to be ratified sometime in 2026. The UN Committee on the Elimination of Racial Discrimination has expressed "deep concern" at the terms of the deal.
Geography
The archipelago is about south of the Maldives, east of the Seychelles, north-east of Rodrigues Island, west of the Cocos Islands, and north of Amsterdam Island.The land area of the islands is, the largest island, Diego Garcia, having an area of. The total area, including lagoons within atolls, is more than, of which are accounted by the Great Chagos Bank, the largest acknowledged atoll structure of the world. The shelf area is, and the Exclusive Economic Zone, which borders the corresponding zone of the Maldives in the north, has an area of .
The Chagos group is a combination of different coralline rock structures topping a submarine ridge running southwards across the centre of the Indian Ocean, formed by volcanoes above the Réunion hotspot. Unlike the Maldives, there is no clearly discernible pattern in the atoll arrangement, which makes the whole archipelago look somewhat chaotic. Most of the coralline structures of the Chagos are submerged reefs.
The Chagos contain the world's largest coral atoll, The Great Chagos Bank, which supports half the total area of good quality reefs in the Indian Ocean. As a result, the ecosystems of the Chagos have so far proven resilient to climate change and environmental disruptions.
The largest individual islands are Diego Garcia, Eagle, , Eastern Egmont, and .
In addition to the seven atolls with dry land reaching at least the high-water mark, there are nine reefs and banks, most of which can be considered permanently submerged atoll structures. The number of atolls in the Chagos Archipelago is given as four or five in most sources, plus two island groups and two single islands, mainly because it is not recognised that the Great Chagos Bank is a huge atoll structure, and because Blenheim Reef, which has islets or cays above or just reaching the high-water mark, is not included. Features are listed in the table from north to south:
Resources
The main natural resources of the area are coconuts and fish. The licensing of commercial fishing used to provide an annual income of about for the British Indian Ocean Territory authorities. No licenses have been given since October 2010, however, and the last expired after the creation of the no-take marine reserve.All economic activity is concentrated on the largest island of Diego Garcia, where joint UK–US military facilities are located. Construction projects and various services needed to support the military installations are done by military and contract employees from the UK, Mauritius, the Philippines, and the US. There are currently no industrial or agricultural activities on the islands. All the water, food and other essentials of daily life are shipped to the island. An independent feasibility study led to the conclusion that resettlement would be "costly and precarious". Another feasibility study, commissioned by organisations supporting resettlement, found that resettlement would be possible at a cost to the British taxpayer of. If the Chagossians return, they plan to re-establish copra production and fishing, and to begin the commercial development of the islands for tourism.
Until October 2010, Skipjack and yellowfin tuna were fished for about two months of the year as their year-long migratory route takes them through Chagos waters. While the remoteness of the Chagos offers some protection from extractive activities, legal and illegal fishing have had an impact, as well as considerable poaching of turtles and other marine life. Sharks, which play a vital role in balancing the food web of tropical reefs, have suffered sharp declines from illegal fishing for their fins and as bycatch in legal fisheries. Sea cucumbers, which cleanse sand, are poached to feed Asian markets.
Climate
The Chagos Archipelago has a tropical oceanic climate; hot and humid but moderated by trade winds.Climate is characterised by plenty of sunshine, warm temperatures, showers and light breezes.
December through February is considered the rainy season ; typical weather conditions include light west-northwesterly winds and warmer temperatures with more rainfall. June to September is considered the drier season, characterised by moderate south-easterly winds, slightly cooler temperatures and less rainfall. The annual mean rainfall is, varying from during August to during January.
History
Early history
According to Southern Maldivian oral tradition, local traders and fishermen were occasionally lost at sea and became stranded in one of the islands of the Chagos. Eventually they were rescued and brought back home. However, these islands were judged to be too far away from the Maldives to be settled permanently by Maldivians. Thus, for many centuries, the Chagos were ignored by their northern neighbours.16th to 19th century
The first Europeans to become aware of the archipelago were Portuguese explorers. Although the Portuguese navigator Pedro de Mascarenhas is credited with having encountered the islands during his voyage of 1512–13, there is little corroborative evidence; cartographic analysis points to 1532 or later. Portuguese seafarers named the group, Chagas referring to the Holy Wounds of the crucifixion of Jesus. They also named some of the atolls, such as Diego Garcia and Peros Banhos Atoll, mentioned as Pedro dos Banhos in 1513 by Afonso de Albuquerque. This lonely and isolated group, economically and politically uninteresting to the Portuguese, was never made part of the Portuguese Empire.The earliest and most interesting description of the Chagos, before coconut trees grew widely on the islands, was written by Manoel Rangel, a castaway from the Portuguese ship Conceição which ran aground on the Peros Banhos reefs in 1556.
The oldest known written document claiming the Chagos is attributed to King Hassan IX of the Maldives in the year 1561. The French were the first European colonial power to lay claim to the Chagos after they settled and Isle de France. The French began issuing permits for companies to establish coconut oil plantations on the Chagos in the 1770s.
On 27 April 1786 the Chagos Islands and Diego Garcia were claimed for Great Britain. However, the territory was ceded to Britain by treaty only after Napoleon's defeat, in 1815. The Chagos were governed from Mauritius, which was by that time also a British colony.
In 1793, when the first successful colony was founded on Diego Garcia, the largest island, coconut plantations were established on many of the atolls and isolated islands of the archipelago. The workers were enslaved by the British and not freed until 1840, after which time many of the workers descended from those who had earlier been enslaved. They formed an inter-island culture called Ilois, a French Creole word meaning.
Commander Robert Moresby made a survey of the Chagos on behalf of the British Admiralty in 1837–1838. After Moresby had taken measurements of most of the atolls and reefs, the archipelago was charted with relative precision for the first time.
Moresby's survey
Robert Moresby was a captain of the East India Company's Bombay Marine/Indian Navy who distinguished himself as a hydrographer, maritime surveyor and draughtsman.
After his completion of the Red Sea Survey, Moresby was sent to chart various coral island groups lying across the track of India-to-Cape trade. In 1834–36 Moresby, assisted by Lieutenants Christopher and Young, undertook the difficult cartography of the Maldive Islands, drawing the first accurate maritime charts of this complicated Indian Ocean atoll group. These charts were printed as three separate large maps by the Hydrographic Service of the Royal Navy.
Moresby's survey of the Atolls of the Maldives was followed by the Chagos Archipelago. where he conducted "a thorough scientific survey". He planted 30 breadfruit trees in Diego Garcia Island, the largest of the group. Moresby reported that "there were cats and chickens on the island".