Saint Helena
- ISS019-E-14918
- 07 May 2009
- 08:37 UTC
Located remotely some 1,950 km off the southwestern coast of Africa, St. Helena is the largest island of the St. Helena group at 122 km². The island has a maximum length of of 16 km (northeast to southwest) and is up to 10 km across. Ascension Island lies 1,125 km to northeast and the Tristan da Cunha Group 1,900 km to the southwest.
The island rises steeply from the ocean floor, as a massive extinct volcano, from depths of over 4,000 m. The emergent part of this mass rises to a maximum height of 823 m above sea level at Diana's Peak. From here, a series of deep ravines, ridges and valleys descend to the coast where they often drop to the sea in tall cliffs that reach heights of 300 m. The formation of the island is thought to have taken place by multiple volcanic events taking place over a period ranging from 7 to 14 million years ago. Since that time the volcano has been inactive, leaving water, wind and rain to shape the island in to its current form.
Located immediately offshore are a number of small islets and emergent rocks, these include: Bird Island, Black Rock, The Buoys, Castle Rock, The Chimney, Egg Island, Flat Rock, Frightus Rock, George Island, Long Ledge, Lower Black Rock, The Needle, Lady's Chair, Lighter Rock, Peaked Island, Rough Rock Island, Shore Island, Sandy Bay Island, Thompson's Valley Island, Upper Black Rock, and White Bird Island.
Much of St. Helena's original flora and fauna has disappeared since human settlement began in the seventeenth century, including the loss of most of the indigenous forest. A programme is underway to re-establish the islands endemic flora — such as the Gumwood (Commidendrum robustum) reforestation project in the Diana's Peak National Park. The island has a number of endemic and rare plants, including 14 species of fern and 6 endemic genera of flowering plants. Species of note include the critically endangered St. Helena Ebony (Trochetiopsis ebenus), St. Helena Olive (Nesiota elliptica) and the medium sized tree the St. Helena Redwood (Trochetiopsis erythroxylon) which is extinct in the wild. The plover-like Wirebird (Charadrius sanctaehelenae) is St. Helena's only surviving native land bird.
image: earth sciences and image analysis laboratory, nasa johnson space center
