Types of islands. Artwork of seagulls flying over different types of volcanic islands. At upper right a large volcanic island was formed by an underwater volcano that grew with each eruption until it broke through the surface of the sea. Plants (green) have started to colonise that island. Over time, as the volcano goes dormant, usually because the motion of tectonic plates moves the island away from the mantle plume causing the volcano, the island erodes away. At lower right, smaller islands have been eroded. Eventually, the islands may end up as coral atolls (lower centre), as the central portion of the island collapses, leaving corals to form the bedrock for the ring of land seen here. See E680/207-209 for a set of images on this topic.