Saint Helena's rugged topography of sharp peaks and deep ravines - evident in this photograph from the International Space Station - is the result of erosion of the volcanic rocks that make up the island. A climatic gradient related to elevation is also evident - the higher, wetter central portion of the island is covered with green vegetation, whereas the lower coastal areas are drier and hotter with little vegetation cover. Image courtesy of NASA.
In the southern Atlantic Ocean roughly midway between central South America and central Africa, sits Ascension Island. A small, rocky, volcanic outcrop covered in many places by lava flows and cinder cones of dormant volcanoes, the island sits just west of the Mid-Atlantic Ridge. In this detailed satellite image taken 24 February 2003, marbled-looking lava flows can be seen dominating the northwest coast, with smaller flows visible on the southwest coast below the island's Wideawake Airfield, as well as on the southeast coast. Northeast of the airstrip, a large cinder cone is visible, its dark brown center fading to tan in a series of pale rings. This crater, the island's largest, is called Devil's Riding School. Crisp, white surf breaks along the shores. Image courtesy of NASA.
An oblique view of rugged Ascension Island, which is is barren in many places and has no indigenous human population. Instead the residents of the island are there because of Ascension's main industry: communications. The island has a long history as a communications hub for telephone and radio communications and as a base for satellite tracking stations, including a NASA station built in the 1960s that no longer operates. The European Space Agency operates a tracking station for its Ariane spacecraft on the eastern side of the island. Ascension Island is one of the most important breeding grounds for seabirds in the tropical Atlantic Ocean. The population of seabirds has been under threat since the first humans sailed up to the island in the 1500s. The ships accidentally introduced black rats, which overran the island, until cats were introduced to curb the rat population. The feral cats have decimated the bird populations, and in fact, are probably responsible for the extinction of two of the islands native land birds. A restoration project is underway to control the cat population and revive the seabirds. Image courtesy of NASA.
The shoreline of the 13 km (8 mi) wide island of Tristan da Cunha is marked on most sides by steep cliffs, with lower beach areas on the southern and north-northwestern sides. The island is notable for its bird population and includes important breeding grounds for petrels, albatrosses, penguins, and shearwaters. Tristan da Cunha is a shield volcano, a volcanic structure with a low, broad profile and composed of silica-poor lavas (such as basalt). The upper surface of this low base appears dark green in this astronaut photograph of 6 February 2013. Steeper brown to tan colored slopes mark the central cone of the volcano at the island's center. The summit crater, Queen Mary's Peak, sits at an elevation of 2,060 m (6,760 ft) above sea level. While geologic evidence indicates that eruptions have occurred from the central crater, lavas have also erupted from flank vents along the sides of the volcano and from smaller cinder cones. The last known eruption of Tristan da Cunha took place in 1961-1962 and forced the evacuation of the only settlement on the island, Edinburgh of the Seven Seas, on the northern coastline (obscured by clouds in this image). The town is considered to be the most remote permanent settlement on Earth, with its nearest neighbor located 2,173 km (1,347 mi) to the northeast on the island of St. Helena. Image courtesy of NASA.