North Keeling Island is a coral atoll 2 km long and 1.3 km wide.

Along with the southern atoll of the Cocos (Keeling) Islands, it formed atop an old volcanic seamount rising 5,000 metres from the ocean floor.

Radiocarbon dating puts the age of the island at between 3,000 and 4,000 years old.

Set around an internal lagoon, North Keeling Island is low and flat with highly calcareous alkaline soil. Beaches on the windward south and east coast are made up almost entirely of coral shingle, while the more sheltered beaches consist of shingle and white sand.

The lagoon makes up most of the island’s interior and has a maximum depth of just two metres. It used to open into the ocean; however, in 2005, natural deposits closed the lagoon entrance. Seawater no longer flows into the lagoon and the former entrance has been colonised by plants and nesting seabirds.