atoll

An atoll is characterized by its distinct circular or oval shape, typically forming a protective barrier around a central lagoon. This geological formation occurs when a coral reef grows around a volcanic island that eventually sinks or erodes, leaving only the ring of coral and sand above sea level. In a geographical context, the term evokes images of isolation, tropical climates, and fragile ecosystems. It is used specifically for these ring-shaped structures, distinguishing them from standard islands or linear reef systems.