Terevaka makes up most of the island, while Poike and Rano Kau form the eastern and southern capes and give the island its triangular shape. They contain many volcanic caves, including pyroducts - natural channels formed by flowing lava. Poike was once a separate island until volcanic material from Teravaka merged it into a larger whole. Iron-rich basalts dominate the island with affinities to magmatic rocks found in the Galapagos Islands.
