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
Haa Alif Atoll to visit each other's islands. Marriage alliances were common. Now Minicoy is a part of India and communication is highly restricted. As an administrative division, North Thiladhunmathi Atoll was created when the huge natural Thiladhunmathi Atoll was administratively divided into northern and southern divisions in 1958. Haa Alif Atoll Haa Alif Atoll is the code name based on the letters of the Maldivian alphabet commonly used to refer to the administrative division officially known as North Thiladhunmathi Atoll (Maldivian: "Thiladhunmathi Uthuruburi") in the Maldives. It is the northernmost of the 19 administrative divisions (known as "Atolls") of the country, and