An atoll is coral reef which forms an almost complete circle around a lagoon.
The circular coral reefs of most atolls reach deep down in to water where no coral can grow. As the diagram shows, atolls may once have been reefs in shallow water surrounding a volcano. As the islands sinks, or the sea level changes , the coral continues to grow. The original island disappears far below the lagoon, and the reef forms an atoll.
The circular coral reefs of most atolls reach deep down in to water where no coral can grow. As the diagram shows, atolls may once have been reefs in shallow water surrounding a volcano. As the islands sinks, or the sea level changes , the coral continues to grow. The original island disappears far below the lagoon, and the reef forms an atoll.
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