Islands differ in their geological and geomorphologic settings; and in their physical, biological, climatic, social, political, cultural, and ethnic characteristics. Yet they share a distinct underlying concern that marks their overall vulnerability in the context of sustainable development.
Bodies of land connected by the continental shelf to a continent. Greenland is part of North American continental shelf, while Tasmania is an extension of the Australian continent. Also, Trinidad is a section of the South American continental shelf while Sumatra is a portion of the South East Asian shelf.
Bodies formed by volcanic eruptions on the ocean floor. As volcanoes erupt, they build up layers of lava that may eventually break the water surface. When the tops of the volcanoes appear above the water, they form islands such as Hawaii made primarily of basaltic lava. Oceanic islands are also known as ‘high islands’ and are usually formed near subduction zones, hot spots, tectonic plates etc.
Bodies that are connected to the mainland at low tide at which time they can be reached on foot. At high tide however they are completely cut off from the mainland making it a true island. Tidal islands are sometimes connected to the mainland by a man-made causeway. Some such islands are Mont Saint-Michel in Normandy, France, Enoshima in Japan, Lindisfarne in the northeast coast of England, etc.
Bodies of low flat land formed in warm waters by tiny sea animals called corals. As corals build up, their hard skeletons make reefs of limestone. Some coral reefs may grow up from a plateau on the seafloor until they break the water’s surface, forming islands. The islands of the Bahamas are the highest parts of underwater banks. Another kind of coral island is the atoll, which is a coral reef that begins by growing in a ring around the sides of an oceanic island. As the island slowly sinks into the sea, the reef continues to grow. Lakshadweep Islands comprise of 12 such atolls.
Bodies of land that is essentially man-made, with material brought-in from elsewhere or as an expanded part of an already-existing island by draining the water around it. Some of the example of artificial islands are Harbor Island in San Diego Bay, California; Treasure Island in Eastern Caribbean, etc. Singapore is actively involved in creating artificial islands apart from other nations such as Qatar and Japan.
Bodies of narrow land that lie parallel to coastlines largely made up of sediments, separated from the shore by a lagoon or a sound. They usually have sand dunes that act as barriers between the ocean and the mainland, which protects the coast from being directly battered by storm waves and winds. The islands off the Atlantic coast of southern Florida were formed in this way. Some barrier islands were formed by glacial deposits from the ice age. Long Island, in New York, and Nantucket, off the coast of Massachusetts, are both formed of glacial moraines. Some of the barrier islands are Galveston and Padre Island, Texas; East Frisian Islands, West Germany.