Geology

Polynesia is characterized by a small amount of land spread over 70.1 million square miles of Pacific Ocean. Most Polynesian islands and archipelagos, including the Hawaiian islands and Samoa, are composed of volcanic islands built by hotspots. New Zealand, Norfolk Island, and Ouvéa, the Polynesian outlier near New Caledonia, are the unsubmerged portions of the largely sunken continent of Zealandia. Zealandia is believed to have mostly sunken by 23 mya and resurfaced geologically recently due to a change in the movements of the Pacific Plate in relation to the Indo-Australian plate, which served to uplift the New Zealand portion. At first, the Pacific plate was subducted under the Australian plate. The Alpine Fault that traverses the South Island is currently a transform fault while the convergent plate boundary from the North Island northwards is a subduction zone called the Kermadec-Tonga Subduction Zone. The volcanism associated with this subduction zone is the origin of the Kermadec and Tongan island archipelagos.
Out of about 117,000 or 118,000 square miles of land, over 103,000 square miles are within New Zealand; the Hawaiian archipelago comprises about half the remainder. The Zealandia continent has approximately 1.4 million square miles of continental shelf. The oldest rocks in the region are found in New Zealand and are believed to be about 510 million years old. The oldest Polynesian rocks outside of Zealandia are to be found in the Hawaiian Emperor Seamount Chain, and are 80 million years old.