Geologically younger than the rest of French Polynesia, the Marquesas archipelago is composed of basaltic massifs exposed to the oceanic swell. The particularly rugged terrain of Ua Pou culminates at 3946ft (1203m) at Mount Oave and alternates cliffs plunging into the sea and wide valleys. The black sand, consisting of yellow-green olivine and black grains, comes from the volcanic rocks of the island.