Raoul is roughly triangular in shape with an area of 29.25 sq km. The center of this island contains a caldera . A second crater lies in the rim of the cliffs that surround the island. These cliffs also encircle half of the nearby bay. A third crater lies east of the main island.
Raoul island is composed of material ejected from several eruption centers.
Most of the early materials erupted from Raoul are andesitic tuffs . The Herald Islets in the east were the first to be active. A later eruption of pumice tuffs covers these andesitic tuffs. Raoul has erupted 14 times. It last erupted in 1965.