Blenheim Reef is a partly submerged

atoll An atoll () is a ring-shaped island, including a coral rim that encircles a lagoon partially or completely. There may be coral islands or cays on the rim. Atolls are located in warm tropical or subtropical oceans and seas where corals can gr ...

structure in the

Chagos Archipelago The Chagos Archipelago () or Chagos Islands (formerly the Bassas de Chagas, and later the Oil Islands) is a group of seven atolls comprising more than 60 islands in the Indian Ocean about 500 kilometres (310 mi) south of the Maldives archi ...

Indian Ocean The Indian Ocean is the third-largest of the world's five oceanic divisions, covering or ~19.8% of the water on Earth's surface. It is bounded by Asia to the north, Africa to the west and Australia to the east. To the south it is bounded by th ...

. It includes the

coral Corals are marine invertebrates within the class Anthozoa of the phylum Cnidaria. They typically form compact colonies of many identical individual polyps. Coral species include the important reef builders that inhabit tropical oceans and sec ...

reef of Baxio Predassa in its southeastern rim, plus another completely submerged part. It is located in the northeastern part of the Chagos Archipelago. It measures almost eleven kilometres (north–south) by more than four kilometres (east–west), with a total area of 36.8 square kilometres, including the

lagoon A lagoon is a shallow body of water separated from a larger body of water by a narrow landform, such as reefs, barrier islands, barrier peninsulas, or isthmuses. Lagoons are commonly divided into ''coastal lagoons'' (or ''barrier lagoons'') a ...

of 8.5 km², the difference being accounted for the mostly by the reef flat. Only on the eastern side, there are a few sand

cay A cay ( ), also spelled caye or key, is a small, low-elevation, sandy island on the surface of a coral reef. Cays occur in tropical environments throughout the Pacific, Atlantic, and Indian Oceans, including in the Caribbean and on the Great ...

s above the water. The largest of them is East Island, which is not quite 200 metres long and 70 metres wide. The other islands in the group are North, Middle and South. Only a few grasses grow on the island. The lagoon is up to 18 metres deep and encumbered with rock. The fringing coral

reef A reef is a ridge or shoal of rock, coral or similar relatively stable material, lying beneath the surface of a natural body of water. Many reefs result from natural, abiotic processes— deposition of sand, wave erosion planing down rock out ...

has a wide passage in the southwest. The closest land is Takamaka Island in the

Salomon Islands The Salomon Islands or Salomon Atoll is a small atoll of the Chagos Archipelago, British Indian Ocean Territory. Description The atoll is located in the northeast of the Chagos Archipelago, between Blenheim Reef and Peros Banhos. The main isla ...

Atoll, about 20 kilometres to the southwest.

British Admiralty The Admiralty was a department of the Government of the United Kingdom responsible for the command of the Royal Navy until 1964, historically under its titular head, the Lord High Admiral – one of the Great Officers of State. For much of it ...

nautical chart A nautical chart is a graphic representation of a sea area and adjacent coastal regions. Depending on the scale of the chart, it may show depths of water and heights of land (topographic map), natural features of the seabed, details of the coa ...

11000030 - 3 Chagos Archipelago, Scale 1:360 000

History

The atoll is thought to have been discovered around 1570 by

Portuguese Portuguese may refer to: * anything of, from, or related to the country and nation of Portugal ** Portuguese cuisine, traditional foods ** Portuguese language, a Romance language *** Portuguese dialects, variants of the Portuguese language ** Portu ...

sailors, which is why it is also known under its Portuguese name Baxio Predassa (a corruption of Baixo Predassa). The present name comes from the ship ''Blenheim'' which discovered the reef on 5 May 1836 during a voyage from London to Bombay (see letter from James Temple Brown to the ''Nautical Magazine and Naval Chronicle'' for 1837). From 1845 to 1860,

guano Guano (Spanish from qu, wanu) is the accumulated excrement of seabirds or bats. As a manure, guano is a highly effective fertilizer due to the high content of nitrogen, phosphate, and potassium, all key nutrients essential for plant growth. G ...

and

phosphate In chemistry, a phosphate is an anion, salt, functional group or ester derived from a phosphoric acid. It most commonly means orthophosphate, a derivative of orthophosphoric acid . The phosphate or orthophosphate ion is derived from phospho ...

were mined. This venture was then given up due to inadequate transport facilities. Around 1880, the Indian Ocean Fruit Company attempted to plant

palm tree The Arecaceae is a family of perennial flowering plants in the monocot order Arecales. Their growth form can be climbers, shrubs, tree-like and stemless plants, all commonly known as palms. Those having a tree-like form are called palm trees ...

s on the island, but all seedlings were washed into the sea during a storm. On 29 June 1975, the atoll was incorporated into the

and claimed by

Mauritius Mauritius ( ; french: Maurice, link=no ; mfe, label=Mauritian Creole, Moris ), officially the Republic of Mauritius, is an island nation in the Indian Ocean about off the southeast coast of the African continent, east of Madagascar. It incl ...

. Before that day, it was not claimed by any nation. On 15 March 1982, the senior British military representative in Diego Garcia landed on Blenheim Reef and raised the British flag, contrary to

Foreign Office Foreign may refer to: Government * Foreign policy, how a country interacts with other countries * Ministry of Foreign Affairs, in many countries ** Foreign Office, a department of the UK government ** Foreign office and foreign minister * Unit ...

instructions which the British Foreign Secretary,

Lord Carrington Peter Alexander Rupert Carington, 6th Baron Carrington, Baron Carington of Upton, (6 June 1919 – 9July 2018), was a British Conservative Party politician and hereditary peer who served as Defence Secretary from 1970 to 1974, Foreign Secret ...

, reaffirmed within hours. The Foreign Office opinion was that the reef wasn’t British territory and could never be, but wanted no publicity which might suggest the idea to other countries. The flag was allowed to deteriorate. In February 2022, Mauritius made a fifteen day expedition to survey the legally unclaimed reef, to discover if it is exposed at high tide so is claimable. In total, there have been 57 shipwrecks around Blenheim Reef, with an estimated 200 lost lives.

Islands

Baxio Predassa is the name given to the islands that emerge from the eastern rim of the reef. When first surveyed by

Robert Moresby Robert Moresby (15 June 1794 – 15 June 1854Some sources mention that he is thought to have died in 1863.) was a captain of the East India Company's Bombay Marine/Indian Navy who distinguished himself as a hydrographer, maritime surveyor a ...

, there were many more islands in Baxio Predassa. These have, however, been eroded or submerged and only four islets remain. The group today consists of: *Ile du Nord, the northernmost island *Ile du Milieu, surrounded by a reef *Ile de l'Est, the largest island and the easternmost island in the atoll. The island has only grasses growing on it, though there was once an unsuccessful attempt to plant palms on the island. *Ile du Sud, the smallest and southernmost islet. It is unvegetated and of no importance

References

External links

further information (in German)Indian Ocean Pilot
{{coord, 5, 12, S, 72, 28, E, type:mountain_region:IO, display=inline,title Atolls of the Chagos Archipelago Uninhabited islands of the British Indian Ocean Territory