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,
Haddhunmathi Atoll Haddhunmathi Atoll Haddhunmathi or Haddummati Atoll (Laamu) is an administrative division of the Maldives. It corresponds to the natural atoll of the same name. It is mostly rimmed by barrier reefs, the broadest of which are topped by islands. There are many islands along its eastern and southern boundaries. This atoll is quite regular excepting for the projection of the reef at its NE corner (Isdhū Muli). It closely resembles Kolhumadulhu, its neighbour further north. Owing to its typical atoll shape, it differs in no respect from atolls in the Pacific Ocean, save for its greater size. Its reefs are