The Cocos (Keeling) Islands lie in the eastern Indian Ocean, about 2,900 kilometers (1,800 miles) northwest of the Australian city of Perth. Comprised of coral atolls and islands, the archipelago includes North Keeling Island and the South Keeling Islands. The Advanced Land Imager (ALI) on NASA’s Earth Observing-1 (EO-1) satellite captured this natural-color image of South Keeling Islands on July 31, 2009.

Coral atolls—which are largely composed of huge colonies of tiny animals such as cnidaria—form around islands. After the islands sink, the coral remains, generally forming complete or partial rings. Only some parts of South Keeling Islands still stand above the water surface. In the north, the ocean overtops the coral.

Along the southern rim of this coral atoll, the shallow water appears aquamarine. Water darkens to navy blue as it deepens toward the central lagoon. Above the water line, coconut palms and other plants form a thick carpet of vegetation.