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
Gaafaru (Kaafu Atoll) Gaafaru (Kaafu Atoll) Gaafaru (Dhivehi: ގާފަރު) is one of the inhabited islands of Kaafu Atoll, the only island of the natural atoll known as Gaafaru. The island is north of the country's capital, Malé. Gahaafaru or Gaafaru (Northern Reef) is a large elliptical reef with only a small inhabited island at its eastern end. This reef has proved disastrous to many vessels. Gaafaru reef is as much a separate atoll as Goifulhafehendhu Atoll or Rasdhukuramathi Atoll which are similar in structure and size. It is separated from Kagi (the northern most island of North Malé Atoll) by a narrow but