Coral reef to form fringing reefs, and can eventually grow become a barrier reef. Where the bottom is rising, fringing reefs can grow around the coast, but coral raised above sea level dies. If the land subsides slowly, the fringing reefs keep pace by growing upwards on a base of older, dead coral, forming a barrier reef enclosing a lagoon between the reef and the land. A barrier reef can encircle an island, and once the island sinks below sea level a roughly circular atoll of growing coral continues to keep up with the sea level, forming a central lagoon. Barrier reefs
Tema Reef 1765. Captain William Williams of the missionary ship "John Williams" sighted the reef on May 15, 1864. It was again examined by in 1880. Tema Reef Tema Reef, also called Tima Reef, is a submerged coral reef in the northern Cook Islands, southeast of Pukapuka. No coral or rock shows above water, but the sea breaks heavily over the reef. The reef measures about , covering a shallow but submerged area of . Legend has it that Tima, an Aitutakian warrior sailed to Nassau, but was chased away by Ngalewu, a chief from Pukapuka. On his return to Aitutaki he