The number of islands in the Pacific Ocean is not known. Every one that is known is shown on the maps used by the captains of ships, but there is doubt about the position and size of several of them. There are islands on which no man has ever landed, and there may be islands which no one has seen.
The maps used in schools show only a few of the Pacific islands; many small islands which stand far away from continents and from larger islands are omitted, and there is not space on the map for showing all of the small islands which form part of a group of islands like Hawaii, Tahiti, and Tonga. Fiji consists of 470 islands, the Tuamotus of an equal number, and the Philippines of more than 7,000. In the whole Pacific there are possibly 30,000 islands, which is more than the islands in all the other four oceans. The Pacific Ocean may be called the Ocean of Islands.
Islands of different sizes and shapes
The islands are of different sizes and different shapes. Some of them are projecting rocks or short high ridges like Molokini, Kaula, and Mokolii; others are low flat masses or broken rings of islets of a few hundred acres in extent, like Laysan and Palmyra islands. There are many islands the size of Oahu or Maui, some of them flat and low and some of them rugged and mountainous. There are many islands larger than any in the Territory of Hawaii. Java is ten times the size of the island of Hawaii; New Caledonia is about the size of Massachusetts; and Borneo is larger than Texas.
The many thousands of islands in the Pacific are of several different kinds. Some of them, like Juan Fernandez ( Robinson Crusoe's island) off the coast of Chile, Vancouver Island adjoining the State of Washington, the Japanese islands on the Asiatic coast, and Papua separated from Australia by the narrow Torres Strait, are continental islands. They consist of about the same kinds of rock and have many of the same plants and animals as the near-lying continents of which they were once a part. Other is ands, like New Zealand, New Caledonia, Fiji, Timor, Borneo, and the Philippines, are little continents in themselves or parts of continents which have been broken up into islands by the sinking of the surrounding land into the sea.
Most of the thousands of islands which rise above the sur ace of the Pacific are oceanic islands; the rocks which compose them and the animals and plants which live on them are different from those on the continents of North America, South America, Asia, and Australia. These oceanic islands include Hawaii, the Marquesas, the Tuamotus, the Austral, Cook, the Society, Tonga, Samoan, Ellice, Gilbert, Marshall, and Caroline Islands and the many small islands scattered between and beyond these groups.
Oceanic islands of the Pacific are of two kinds, volcanic islands and coral islands. Volcanic islands are composed of lava which has issued in a molten state from vents in the bottom of the sea and spread out over the sea floor, building up a mound of rock. In places where lava continues to come from the interior of the earth the mound may be built up until it stands above the surface of the water. Continued supply of lava may make this mound into a huge mass of lava, a volcano, which may remain as a mountain long after lava has ceased to flow. Some volcanic islands consist of one volcano; others have been made by the combined activities of many volcanoes. The kind of lava rock which composes the volcanic islands of the Pacific is basalt and is different from that which forms volcanic islands in some other parts of the world.
Coral islands are composed of limestone made of whole shells and parts of broken shells of many small animals which live in the sea and of algae, sea plants, of several kinds. Of the animals which form limestone, corals are the most abundant. The beginning of a coral island is a mass of land which rises nearly to the surface of the sea. To this land corals attach themselves and begin to spread and to grow upward nearly to the water's surface. Corals also attach themselves to the edges of continents, continental islands, and volcanic islands, forming reefs which border the shore and extend some distance seaward. Coral islands are not found everywhere, because corals can live only in warm, shallow, and clear salt water. No corals grow in New Zealand or in the Aleutian Islands because the water is too cold; and none grow near the mouths of fresh-water streams or of muddy streams.
Corals by themselves make coral reefs which may be exposed at low tides, though they do not make coral islands, for they die when out of water. But waves may break up a coral reef and make an island by piling the broken fragments so high that their top is above high tides. The waves not only break large chunks from the reef but also grind the corals and shells into sand. This sand is carried by the wind and built into sand dunes, which make the new islands still higher and wider and provide a soil in which plants may grow. These islands made by the waves and the wind working together have various forms; some are straight narrow belts of land; others are shaped like a circle or a horseshoe; but all of them are low islands with the highest points not more than twenty or thirty feet above sea level.
Raised coral islands
The sea bottom beneath some coral reefs in the Pacific has risen toward the surface of the water, carrying the reefs up with it, thus making islands of coral and shell which may stand as high as one hundred feet or even more above sea level. Such islands are called raised coral islands.
Some islands better than others
As places for men to live these three kinds of oceanic islands are very different. The soil of coral islands and of raised coral islands is made of decomposed limestone; that of volcanic islands is volcanic dust and sand and mud made from decomposed lava. Little rain falls on coral islands, more on raised coral islands, and the most on volcanic islands. The plants, insects, and land shells are different on the three kinds of islands.