Atoll Atoll An atoll (, , , , or ), sometimes called a coral atoll, is a ring-shaped coral reef including a coral rim that encircles a lagoon partially or completely. There may be coral islands or cays on the rim. The coral of the atoll often sits atop the rim of an extinct seamount or volcano which has eroded or subsided partially beneath the water. The lagoon forms over the volcanic crater or caldera while the higher rim remains above water(s) or at shallow depths that permit the coral to grow and form the reefs. For the atoll to persist,
Haa Alif Atoll Secretariat of North Thiladhunmathi Atoll Council is located. The Northern Thiladhunmathi Atoll administrative division consists of a total of 43 islands spread over two natural geographic atolls, namely Northern Thiladhunmathi, and Ihavandhippolhu. Northern Thiladhunmathi is the northern-most portion of the huge Thiladhunmathi Atoll. Thiladhunmathi Atoll was administratively divided into northern and southern divisions in 1958. Ihavandhippolhu lies to the north of Northern Thiladhunmathi, with the Ihavandhoo Kandu channel separating the two, and is the northern-most atoll of the Maldives. It is a small natural atoll 22 km in length. It has 25 islands lying all around the boundary reef. One