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
Laamu Atoll Laamu Atoll Laamu Atoll (also known as Haddhunmathi Atoll) is an administrative division of the Maldives. It corresponds to the natural atoll of the same name. The administrative capital is located in Fonadhoo Island. Traditionally, Maldivians call this atoll simply 'Haddhunmathi', without adding the word 'Atholhu' at the end. It is mostly rimmed by barrier reefs, the broadest of which are topped by islands. There are many islands along its eastern and southern boundaries. This atoll is quite regular excepting for the projection of the reef at its NE corner (Isdhū Muli). It closely resembles Kolhumadulhu, its neighbour further north.