atoll

views updated May 23 2018

atoll Ring-shaped reef of coral enclosing a shallow lagoon. An atoll begins as a reef surrounding a slowly subsiding island, usually volcanic. As the island sinks, the coral continues to grow upwards until eventually the island is below sea level and only a ring of coral is left at the surface.

http://nasa.gov/Study/Maldives/maldives.html

atoll

views updated May 08 2018

atoll Ring-shaped organic reef that encloses or almost encloses a lagoon, and which is surrounded by the open sea. The reef may be built of coral and/or calcareous algae. An atoll is built on an existing structure such as an extinct, submerged volcano.

atoll

views updated Jun 27 2018

atoll A ring-shaped organic reef that encloses or almost encloses a lagoon and which is surrounded by the open sea. The reef may be built of coral and/or calcareous algae. An atoll is built on an existing structure such as an extinct, submerged volcano.

atoll

views updated May 23 2018

at·oll / ˈatˌôl; ˈatˌäl; ˈāˌtôl; ˈāˌtäl/ • n. a ring-shaped reef, island, or chain of islands formed of coral.

atoll

views updated May 14 2018

atoll ring-shaped coral reef enclosing a lagoon. XIX (in XVII as atollon). — Maldive atoḷu.