The Pitcairn Islands form the southeasternmost extension of the geological archipelago of the Tuamotus of French Polynesia, and consist of four islands: Pitcairn Island, Oeno Island (atoll with five islets, one of which is Sandy Island), Henderson Island and Ducie Island (atoll with four islets).
The Pitcairn Islands were formed by a centre of upwelling magma called the Pitcairn hotspot.
The only permanently inhabited island, Pitcairn, is accessible only by boat through Bounty Bay. Henderson Island, covering about 86% of the territory's total land area and supporting a rich variety of animals in its nearly inaccessible interior, is also capable of supporting a small human population despite its scarce fresh water, but access is difficult, owing to its outer shores being steep limestone cliffs covered by sharp coral. In 1988 this island was designated as a UNESCO World Heritage site.[23] The other islands are at a distance of more than 100 km (62 mi) and are not habitable.