Made from coral reefs and sand, Diego Garcia is one of these ring-shaped islands surrounding a lagoon
These 
masses are especially numerous, and most linear along the edge of .... and at 
last appeared as a ring of coral with a central lagoon, owing to a slow ..... entirely 
surrounded by dry land, or nearly so, as is the case at Diego Garcia,... [DOC] [TLE] Reef-island topography and the vulnerability of atolls to sea-level rise [PAR] vulnerability of atoll reef islands to sea-level rise (e.g.