Saint Helena is an island in the

South Atlantic Ocean The Atlantic Ocean is the second-largest of the world's five oceans, with an area of about . It covers approximately 20% of Earth's surface and about 29% of its water surface area. It is known to separate the "Old World" of Africa, Europe and ...

, about midway between

South America South America is a continent entirely in the Western Hemisphere and mostly in the Southern Hemisphere, with a relatively small portion in the Northern Hemisphere at the northern tip of the continent. It can also be described as the southe ...

and

Africa Africa is the world's second-largest and second-most populous continent, after Asia in both cases. At about 30.3 million km2 (11.7 million square miles) including adjacent islands, it covers 6% of Earth's total surface area ...

. St Helena has a land area of 122 square kilometres and is part of the territory of

Saint Helena, Ascension and Tristan da Cunha Saint Helena, Ascension and Tristan da Cunha is a British Overseas Territory located in the South Atlantic and consisting of the island of Saint Helena, Ascension Island and the archipelago of Tristan da Cunha including Gough Island. Its name wa ...

which includes

Ascension Island Ascension Island is an isolated volcanic island, 7°56′ south of the Equator in the South Atlantic Ocean. It is about from the coast of Africa and from the coast of South America. It is governed as part of the British Overseas Territory o ...

and the island group of

Tristan da Cunha Tristan da Cunha (), colloquially Tristan, is a remote group of volcanic islands in the South Atlantic Ocean. It is the most remote inhabited archipelago in the world, lying approximately from Cape Town in South Africa, from Saint Helena ...

Physical geography

Climate

The climate of

Saint Helena Saint Helena () is a British overseas territory located in the South Atlantic Ocean. It is a remote volcanic tropical island west of the coast of south-western Africa, and east of Rio de Janeiro in South America. It is one of three constitu ...

island can be described as tropical, marine and mild, tempered by the Benguela Current and

trade winds The trade winds or easterlies are the permanent east-to-west prevailing winds that flow in the Earth's equatorial region. The trade winds blow mainly from the northeast in the Northern Hemisphere and from the southeast in the Southern Hemisph ...

which blow almost continuously. Similarly, the climate of

is marine, mild and also tempered by trade winds, although the climate is temperate in nature. Ascension Island is warmer and wetter than St Helena.

Terrain

has a rugged,

volcanic A volcano is a rupture in the crust of a planetary-mass object, such as Earth, that allows hot lava, volcanic ash, and gases to escape from a magma chamber below the surface. On Earth, volcanoes are most often found where tectonic plates a ...

terrain, with small scattered

plateau In geology and physical geography, a plateau (; ; ), also called a high plain or a tableland, is an area of a highland consisting of flat terrain that is raised sharply above the surrounding area on at least one side. Often one or more sides ha ...

s and

plain In geography, a plain is a flat expanse of land that generally does not change much in elevation, and is primarily treeless. Plains occur as lowlands along valleys or at the base of mountains, as coastal plains, and as plateaus or uplands ...

s, with the largest area of level ground on the island being Prosperous Bay Plain in the eastern arid area. The other islands of the group have a volcanic origin. The highest point on the island is Diana's Peak at 818 metres (2,684 ft), though Queen Mary's Peak on

is the highest in the British territory at 2,062 m. A natural hazard on Tristan da Cunha is active volcanism, though this is not the case on St Helena itself.

Geology

St. Helena exists because of the St. Helena hotspot which began to produce basaltic lava about 145 million years ago when it was near the constructive plate margin of the

Mid-Atlantic Ridge The Mid-Atlantic Ridge is a mid-ocean ridge (a divergent or constructive plate boundary) located along the floor of the Atlantic Ocean, and part of the longest mountain range in the world. In the North Atlantic, the ridge separates the North Ame ...

. The movement of the

African Plate The African Plate is a major tectonic plate that includes much of the continent of Africa (except for its easternmost part) and the adjacent oceanic crust to the west and south. It is bounded by the North American Plate and South American Plat ...

away from the hotspot has left the chain of the St. Helena

seamounts A seamount is a large geologic landform that rises from the ocean floor that does not reach to the water's surface (sea level), and thus is not an island, islet or cliff-rock. Seamounts are typically formed from extinct volcanoes that rise abru ...

, which may connect with the Cameroon Volcanic Line. St. Helena, the most south westerly point on the chain, is close to the plate margin, but the last volcanic eruptions occurred about 7 million years ago. The first investigations of St. Helena geology were made when

Charles Darwin Charles Robert Darwin ( ; 12 February 1809 – 19 April 1882) was an English naturalist, geologist, and biologist, widely known for his contributions to evolutionary biology. His proposition that all species of life have descended fr ...

visited the island on the voyage of

H.M.S. Beagle HMS ''Beagle'' was a 10-gun sloop-of-war#Rigging, brig-sloop of the Royal Navy, one of more than 100 ships of this class. The vessel, constructed at a cost of £7,803 (roughly equivalent to £ in 2018), was ship naming and launching, launched ...

in July 1836. He "used the observations on St Helena to formulate an intermediate hypothesis (published in 1844 in his book "Geological Observations on the volcanic islands and parts of South America visited during the Voyage of H.M.S. "Beagle") - volcanoes rise by slow, gradual and episodic events".

Geological features

The Barn is a capping of younger lavas upon weaker rocks. The Barn features cliffs on the side that faces the sea. It overlooks the pyroclasts and weak flows of Turk's Cap Valley to the south. Taking their names from the story of

Lot Lot or LOT or The Lot or ''similar'' may refer to: Common meanings Areas * Land lot, an area of land * Parking lot, for automobiles *Backlot, in movie production Sets of items *Lot number, in batch production *Lot, a set of goods for sale togethe ...

in the Book of Genesis, "Lot" and "Lot's Wife" are two solitary pillars of rock topping two valleys near Sandy Bay. The pillars are

phonolitic Phonolite is an uncommon extrusive rock, of intermediate chemical composition between felsic and mafic, with texture ranging from aphanitic (fine-grained) to porphyritic (mixed fine- and coarse-grained). Phonolite is a variation of the igneous ...

intrusion In geology, an igneous intrusion (or intrusive body or simply intrusion) is a body of intrusive igneous rock that forms by crystallization of magma slowly cooling below the surface of the Earth. Intrusions have a wide variety of forms and com ...

s, which are more resistant to erosion than surrounding volcanic features which have, in time, eroded away.

Natural resources

Saint Helena possesses

fish Fish are aquatic, craniate, gill-bearing animals that lack limbs with digits. Included in this definition are the living hagfish, lampreys, and cartilaginous and bony fish as well as various extinct related groups. Approximately 95% of li ...

as a main natural resource. Land use in the island group is divided between

arable land Arable land (from the la, arabilis, "able to be ploughed") is any land capable of being ploughed and used to grow crops.''Oxford English Dictionary'', "arable, ''adj''. and ''n.''" Oxford University Press (Oxford), 2013. Alternatively, for the ...

(with 12.9% of the area given to this) and other uses, which occupy the remaining 87.1%. In terms of maritime claims, St Helena has an exclusive fishing zone of 200 nautical miles, and a territorial sea of twelve nautical miles.

Islands

Just off the coast of St Helena island itself are numerous small islands. Starting from the north and running clockwise, these are: Shore Island, George Island, Rough Rock Island, Flat Rock, The Buoys, Sandy Bay Island, Black Horse Island, White Bird Island, Frightus Island, Jar Rock, Castle Point Rock, Robert Rock, Salt Rock, Speery Island, Flat Rock, The Needle, Lower and Upper Black Rock, Bird Island, Black Rock, Thompson's Valley Island, Peaked Island, Egg Island, Lady's Chair, Lighter Rock, Long Ledge, and Red Rock.

Ecology

Saint Helena harbours at least 40 species of plants unknown anywhere else in the world, and Ascension is a breeding ground for

sea turtle Sea turtles (superfamily Chelonioidea), sometimes called marine turtles, are reptiles of the order Testudines and of the suborder Cryptodira. The seven existing species of sea turtles are the flatback, green, hawksbill, leatherback, loggerhead, ...

s and

sooty tern The sooty tern (''Onychoprion fuscatus'') is a seabird in the family Laridae. It is a bird of the tropical oceans, returning to land only to breed on islands throughout the equatorial zone. Taxonomy The sooty tern was described by Carl Linnaeu ...

Districts

The island of St Helena is divided into 8 districts,GeoHive
St Helena which are used for electoral and administrative purposes.

References

External links

* {{Geography of Africa

Geography of Saint Helena, Ascension and Tristan da Cunha