Rurutu

Rūrutu is the northernmost island in the Austral archipelago of French Polynesia, and the name of a commune consisting solely of that island. It is situated 572 km south of Tahiti.

Geologically, Rurutu was initially formed 12 million years ago by the Macdonald hotspot, a hotspot associated with the Macdonald seamount. Over the next 10 million years, erosion shrank the island until it was almost an atoll. Then, just over a million years ago, Rurutu passed over the Arago hotspot, which lifted it roughly 150 meters. Steep sea cliffs of ancient coral lifted by the event — called makatea — now largely encircle the island. These are riddled with caves filled with concretions — indeed, Rurutu is largely unique among islands in French Polynesia in that its historic inhabitants were cave-dwelling.