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
Kolhumadulu Atoll Kolhumadulu Atoll Kolhumadulu Atoll (also known as Thaa Atoll) is an administrative division of the Maldives. It corresponds to the natural atoll of the same name. The ancient name of the island was Kolhumaduva during the time of King Koimala who united all atolls of the Maldives under one kingdom for the first time. Traditionally, Maldivians call this atoll simply Kolhumadulu, without adding the word "atholhu" at the end. Thaa is the code letters assigned to the atoll and is sometimes used by tourists to refer to the atoll itself. The waters surrounding this atoll are good fishing areas and