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
Northern Thiladhunmathi Atoll Northern Thiladhunmathi Atoll Haa Alif Atoll - officially referred as Thiladhunmathi Uthuruburi (Northern Thiladhunmathi Atoll) is the northernmost administrative division of the Maldives. As the administrative division known as Haa Alif it includes Ihavandhippolhu, the northernmost natural atoll of the Maldive archipelago, as well as a section of the larger Thiladhunmathi or Tiladummati Atoll. Thiladhunmathi was divided into its northern and southern divisions on May 21, 1958. The north division was integrated with Ihavandhippolhu forming administratively a new atoll called Haa Alif atoll or Thiladhumathi North. In total Haa Alif atoll contains 42 islands, 14 of which are inhabited.At present