Ring Shaped reef crossword clue

Ring-shaped reef crossword clue. a New Zealand CROSSWORD question in The Dominion Post on 6 Jun 2017, 5 letters.

The answer: ATOLL

An atoll is a ring-shaped coral reef, island, or series of islets. An atoll surrounds a body of water called a lagoon. Sometimes, atolls and lagoons protect a central island. Channels between islets connect a lagoon to the open ocean or sea.

Atolls develop with underwater volcanoes, called seamounts. First, the volcano erupts, piling up lava on the seafloor. As the volcano continues to erupt, the seamount’s elevation grows higher, eventually breaking the surface of the water. The top of the volcano becomes an oceanic island.