A type of island consisting of a ribbon reef that nearly or entirely surrounds a lagoon and supports, in most cases, one to many islets on the reef platform. Atolls have a unique geology, so not all islands with a reef and a lagoon are atolls
One of three geomorphologically distinct types of coral reefs, the other two being fringing reefs and barrier reefs An atoll is an annular reef formed around a subsiding volcanic island See Barnes and Hughes (1988)
circular, or near circular coral reef appearing as a low coral island or a ring of closely spaced coral islets encircling a shallow lagoon in which there is no pre-existing land, and surrounded by deep water of the open sea, formed above an underwater volcano
Coral reefs sometimes grow around seamounts that rise above the surface of the ocean As the seamount sinks or its peak erodes, the seamount will disappear beneath the water leaving the coral ring
A coral reef appearing in plan view as roughly circular, and surmounted by a chain of closely spaced, low coral islets that encircle or nearly encircle a shallow lagoon in which there is no land or islands of non-coral origin; the reef is surrounded by open sea GG
A circular reef that encloses a relatively shallow lagoon and extends from a very great depth to the sea surface An atoll forms when an oceanic island ringed by a barrier reef sinks below sea level
An atoll is a ring of coral rock, or a group of coral islands surrounding a lagoon. a coral island in the shape of a ring (atolu). Coral reef enclosing a lagoon. Atolls consist of ribbons of reef that may not be circular but that are closed shapes, sometimes miles across, around a lagoon that may be 160 ft (50 m) deep or more. Most of the reef itself is usually below the water surface; around the rim along the top are usually low, flat islands or more continuous strips of low, flat land
A massive coral growth on a submerged mountain range or volcano, common in the Indian and Pacific Oceans The only English word derived from the Maldivian language, an atoll is a large coral reef, containing low inhabitable islands, encircling a sea water lagoon