At high tide only a few rocks show above the waterline at Bassas da India. When the tide ebbs, it exposes a ring of coral 300 feet wide and six miles in diameter. This atoll is the summit of an undersea volcano that rises from the seabed 10,000 feet below the surface.

A million pairs of seabirds, including sooty terns, red-footed boobies, and two species of frigatebird, breed on Europa, and several thousand green turtles nest on its beaches. Unlike Bassas da India, which is uninhabitable, Europa hosts French troops.

Maps: Virginia W. Mason, NGM Staff
Sources: Terres Australes et Antarctiques Françaises; Direction Régionale de L’Environnement, Réunion; CIA; DigitalGlobe