It extends for 16 km in length and 12 km in maximum width, with an area of 122 km². The island is of volcanic origin, consisting of the emerged part of an ancient submarine volcano, whose crater descends to the sea from three sides, while the fourth side is located almost at sea level. The highest peak is Diana’s Peak, 824 m high, from which they descend steeply towards the sea, narrow and deep valleys.
It is a hot spot on the line that divides the African plate from the American plate: along this line the magma reaches the surface and pushes the two plates that move away.
There are several rocks and islets off the coast, including: Castle Rock, Speery Island, The Needle, Lower Black Rock, Upper Black Rock (south), Bird Island (southwest), Black Rock, Thompson’s Valley Island, Peaked Island, Egg Island, Lady’s Chair, Lighter Rock (west), Long Ledge (northwest), Shore Island, George Island, Rough Rock Island, Flat Rock (east), The Buoys, Sandy Bay Island, The Chimney, White Bird Island and Frightus Rock (southeast), all of which are less than a kilometer from the coast.