Islands of the Pacific Ocean
The Pacific Ocean is the largest body of water on Earth — covering one-third of its surface, with a surface area in the region of 180 million km². Its waters contain an unknown number of islands and reefs, the vast majority of which are found in the southern and western sectors, leaving the eastern and northern Pacific regions with relatively few islands in comparison. The number of islands within the Pacific is often estimated to be between 20,000 and 30,000, although the true figure is likely far greater.
Around the western margins of the Pacific are numerous marginal and regional seas, such as the Bo Hai Sea, Bohol Sea, Coral Sea, Gulf of Carpentaria, Sea of Okhotsk, Sulu Sea, and Yellow Sea.
In the north, northeast and northwest are the volcanic island-arc systems that form part of the Pacific Ring of Fire, including the Aleutian Islands, Kuril Islands, the islands of Japan and the islands of the Izu-Bonin-Mariana arc. Also in the west are the large collections of reefs and islets of the South China Sea. In the east, off the South American coast, are the Galapagos Islands and several isolated groups and solitary islands. In the west and southwest are the three great groupings that are traditionally used to describe the islands of the Pacific: Micronesia, Melanesia and Polynesia. These groups, together, form the super-region often known as Oceania.
The islands of Melanesia include the large island of New Guinea (at 785,753 km² in area, it is the largest island in the Pacific), and extending to the southeast the many islands of New Caledonia, the Solomon Islands and Vanuatu; at the eastern extremities of Melanesia the great archipelago of Fiji is included also. Melanesian islands are generally large, hilly or mountainous, often volcanically active, and thickly forested. Smaller, low-lying islands and reefs are also present.
North of the equator and spreading in a great east to west zone are the numerous atolls, reefs and sunken banks that make up the bulk of the region known as Micronesia. The main groups here include the Caroline Islands, Marshall Islands, and the Kiribati groups of the Gilbert, Rawaki and Line Islands. These groups, although predominantly composed of low-lying atoll formations, also contain a few mountainous islands such as those of Kosrae and Pohnpei in the Caroline Islands. Also included within Micronesia is the volcanic arc of the Mariana Islands, Palau in the southwest (south of the equator) and the isolated Wake Atoll in the northeast.
The islands of Polynesia stretch from New Zealand in the southwestern corner of the Pacific to the Hawaiian Islands in the northeast. It contains a wide variety of island types from the high, volcanically active islands of groups such as the Hawaiian Islands and Samoa to the low-lying atolls and coral islets of the northern Cook Islands and the Tuamotu Archipelago. Polynesia includes Tonga, Tuvalu, the Society Islands, the remote Easter Island, the Marquesas, the Line Islands (which are also sometimes described as being part of Micronesia) and the Tubuai Islands, as well as a number of smaller groups and solitary islands.
The fourth great grouping of islands are those that lie within or around the many marginal seas that connect the Pacific and Indian oceans. In what is sometimes known as the Australasian Mediterranean Sea, are located the vast collections of islands and reefs that comprise the nations of Indonesia and the Philippines.