As per Darwin's theory about the formation of coral atolls, this illustration shows the remaining coral atoll following subsidence of the original volcanic island.
Illustration of a 3D watershed with river mouth, continental islands, coral reef, and beach
Illustration of a 3D watershed with braided river, continental islands, coral reef, and beach
Illustration of reef base with volcanic island and barrier reef
Illustration of reef base with volcanic island and fringing reef