The basal diameter of the volcanic edifice is some 60 km, and only the topmost and youngest few percent of the volcanic structure is exposed above sea level.
Nothing is known of the submerged part of the volcano.
Ascension Island has an area of 98 square kilometres and a varied topography, being generally higher and more rugged in the central and eastern parts of the island. Ascension is arid and barren, although in recent years vegetation has spread somewhat from Green Mountain to lower elevations. Profile of Ascension Island seen from the south. In excess of 50 scoria cones dot the surface of Ascension. All of the cones have an oxidized surface layer, and some are pervasively oxidized.