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 Dhaalu Atoll Haa Dhaalu Atoll Haa Dhaalu Atoll is the code name based on the letters of the Maldivian alphabet commonly used to refer to the administrative division (known as "Atoll") officially known as South Thiladhunmathi Atoll (Maldivian: "Thiladhunmathi Dhekunuburi") in the Maldives. The administrative division consists of the southern section of natural Thiladhunmathi Atoll (which is shared with North Thiladhunmathi (Haa Alifu) Atoll) and Makunudhoo or Maamakunudhoo Atoll (Malcolm Atoll in the Admiralty Charts) with its large reef. The capital of the administrative division is Kulhudhuffushi. Thiladhunmathi Atoll was divided into northern and southern divisions on 21 May 1958, thus creating