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,
Kolhumadulu Atoll Kolhumadulu Atoll Kolhumadulu Atoll (also known as Thaa Atoll) is an administrative division of the Maldives. It corresponds to the natural atoll of the same name. The ancient name of the island was Kolhumaduva during the time of King Koimala who united all atolls of the Maldives under one kingdom for the first time. Traditionally, Maldivians call this atoll simply Kolhumadulu, without adding the word "atholhu" at the end. Thaa is the code letters assigned to the atoll and is sometimes used by tourists to refer to the atoll itself. The waters surrounding this atoll are good fishing areas and