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,
Bikini Atoll Bikini Atoll Bikini Atoll (pronounced or ; Marshallese: ", , meaning "coconut place") is an atoll in the Marshall Islands which consists of 23 islands totalling surrounding a central lagoon. It is at the northern end of the Ralik Chain, approximately northwest of Ailinginae Atoll and northwest of Majuro. Within Bikini Atoll, Bikini, Eneu, Namu and Enidrik islands comprise just over 70% of the land area. Bikini and Eneu are the only islands of the atoll that hosted a permanent population. Bikini Island is the northeastern most and largest islet. Before World War II, the atoll was known by its