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,
Johnston Atoll Johnston Atoll Johnston Atoll, also known as Kalama Atoll to Native Hawaiians, is an unincorporated territory of the United States currently administered by the United States Fish and Wildlife Service. Johnston Atoll is a National Wildlife Refuge and is closed to public entry. Limited access for management needs is only by Letter of Authorization from the U.S. Air Force and Special Use Permit from the U.S. Fish and Wildlife Service. For nearly 70 years, the atoll was under the control of the U.S. military. During that time, it was variously used as a naval refueling depot, an airbase, a nuclear