Ascension
- ISS006-E-40765
- 26 March 2003
- 17:16 UTC
Located in the equatorial regions of the Atlantic Ocean, around 80 km west of the mid-Atlantic Ridge and 1,125 km northwest from St. Helena, the island of Ascension is the second largest and most important of the St. Helena group. The island covers an area of 98 km², measuring 17 km across. Offshore lie a number of smaller islets and emergent rocks, including Boatswain Bird Island and Boatswain Bird Rock.
Ascension Island is the summit of large dormant volcano that rises from the sea floor over 3,000 m below. The volcano is around 6 to 7 million years old and has been highly active for most of its life, so that the oldest rocks found on the island today are all less than one million years old, making it one of the Atlantic's youngest islands. However, there has been no historically recorded volcanic events on Ascension — the last major volcanic eruption taking place about 600-700 years ago.
Much of the surface of the island has a barren desert-like landscape, composed of bare basalt lava flows, that is dotted with numerous scoria cones. These small peaks — often with small craters — are composed of volcanic cinders and blocks. They usually have colours of reddish brown due their surface layers being heavily oxidised — many of these can be seen in the above image. They include Red Hill (223 m), Broken Tooth (228 m) and Sisters Peak (446 m). In the eastern and central parts of the island the terrain is more rugged and vegetated, rising to 859 m at Green Mountain. Other topographical features include the plains that descend gently to the northwest coast where sand-lined beaches are found, and the tall cliffs of the southeastern coast.
Vegetation is primarily found in the vicinity of Green Mountain, although the more barren areas are slowly being colonised. Rare endemic plant species include the critically endangered Ascension spurge (Euphorbia origanoides), and the ferns Asplenium ascensionis, Pteris adscensionis and Marattia purpurascens.
The island is an important nesting and breeding site for Atlantic seabirds. Species include the Black Noddy (Arious tenuirestris), Sooty Tern (Sterna fuscata), the endemic Ascension Frigatebird (Fregata aquila), White Booby (Sula dactylatra), Fairy Tern (Gygis alba), Brown Booby (Sula leucogasta), and the Madeiran Petrel (Oceanodroma castra). Since the introduction of feral species when the island was settled in 1815 most species have become confined to inaccessible cliffs and offshore islets where they exist in much reduced numbers. Ascension's beaches are used as nesting sites by Green (Chelonia mydas) and Hawksbill (Eretomochelys imbricata) turtles.
image: earth sciences and image analysis laboratory, nasa johnson space center
