Atoll remains of an ancient atoll as a hill in a limestone area is called a reef knoll. The second largest atoll by dry land area is Aldabra with 155 km². The largest atoll in terms of island numbers is Huvadhu Atoll in the south of the Maldives with 255 islands. In 1842, Charles Darwin explained the creation of coral atolls in the southern Pacific Ocean based upon observations made during a five-year voyage aboard from 1831 to 1836. Accepted as basically correct, his explanation involved considering that several tropical island types—from high volcanic island, through barrier reef island, to atoll—represented
Kaafu Atoll do not form part of the Kaafu Atoll administrative division and are a separate administrative division. Kaafu is a code letter of the Thaana alphabet used in the Maldivian language, Dhivehi, assigned to one of the administrative divisions of the Maldives which is officially and traditionally known by the name Malé Atoll. The Thaana alphabet code names are not the names of the natural or geographical atolls of the Maldives which make up these divisions. These administrative divisions may consist of part of, a single or several natural atolls. Malé Atoll is the name of two natural atolls which form