Mangaia

Mangaia (51.08 sq.km/31.66mi; up to 169m/554ft), the most southerly and the second-largest island in the archipelago, is in the shape of an irregular circle. The lower slopes of the central volcanic ridge are deeply indented by rivers. Round the central core are numerous irregularly shaped swampy depressions up to 366m/1200ft across, bounded at the lower end by limestone cliffs up to 60m/197ft high, sometimes dropping almost vertically. The cliffs are part of the 1.2-1.6km/.7-1mi wide plain of coralline limestone (makatea), much affected by karstic action, which surrounds the island's volcanic core. The water flowing down from the hills seeps away into dolines and extensive cave systems, to re-emerge on the shore or in karstic springs near the coast.

The island is well provided with roads and tracks. Its fertile volcanic soil yields good yields of pineapples, coffee and other tropical produce for export.

There are three small settlements on the island, Oneroa, Tamarua, and Ivirua. As with the rest of the Cook Islands, Mangaia is struggling to deal with a declining population. The island had a population of 2,000 in the 1960s and today is home to less than 500 people.