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,
Baa Atoll Biosphere Reserve the environment. Baa Atoll has a warm and humid tropical climate. The weather is dominated by two monsoon periods – a rainy monsoon period, which lasts from May to November, and a dry monsoon period, which lasts from January to March. The dominant natural environment of the reserve is marine, surrounded by deep ocean. The water depth varies considerably and includes lagoons with depths ranging from 30 m to 80 m, opening into the Indian Ocean, while channels running through the atoll may be up to 250-300 m in depth. The lagoons enclose a variety of reef structures including faros,