North of the equator and west of the international date line are the numerous small islands of Micronesia, including the Caroline Islands, the Marshall Islands, and the Mariana Islands. In the southwestern corner of the Pacific lie the islands of Melanesia, dominated by New Guinea. Other important island groups of Melanesia include the Bismarck Archipelago, Fiji, New Caledonia, the Solomon Islands, and Vanuatu. Continental islands lie outside the Andesite Line and include New Guinea, the islands of New Zealand, and the Philippines. These islands are structurally associated with the nearby continents.
High islands are of volcanic origin, and many contain active volcanoes.
Among these are Bougainville, Hawaii, and the Solomon Islands. The third and fourth types of islands are both the result of coralline island building. Coral reefs are low-lying structures that have built up on basaltic lava flows under the ocean's surface. A second island type formed of coral is the uplifted coral platform, which is usually slightly larger than the low coral islands. Important human migrations occurred in the Pacific in prehistoric times, most notably those of Polynesians from Tahiti to Hawaii and New Zealand.