If you were stranded on an island and you could only bring one thing with you, what would it be? Surely, you would have heard this question before.
The Earth is more than 70 percent water, so you can imagine there are a lot of islands around the world.
In this lesson, let's explore more about the topic island. We will learn
An island is an area of land that is entirely surrounded by water and does not touch any land. Islands may occur in oceans, seas, lakes or rivers.
Islands are sometimes known by different names. Very small islands such as emergent land features on atolls can be called islets, skerries, cays or keys. An island in a river or a lake island may be called an eyot or ait, and a small island off the coast may be called a holm. Sedimentary islands in the Ganges delta are called chars. Very small islands are called 'islets'.
The most notable difference between a continent and an island is in their size. Continents can span a huge amount of landmass and can include numerous countries - they can also be separated by countries with respect to physical and political borders. In contrast, an island has the generic description as a small landmass surrounded by bodies of water on each side.
An Island is a continental land that is surrounded by water on all its sides. There are different names depending upon the size of this land and the water body surrounding it. A continent is a large land mass that has specified geographical boundaries and is separated by oceans.
Continents are also surrounded by water, but because they are so big, they are not considered islands.
There are six major types of islands - Continental, Oceanic, Tidal, Barrier, Coral and Artificial.
Some islands are formed on the continental shelf (very close to the coastline) and they are continental islands. Others are formed far from the continental shelf (in the ocean), and they are known as oceanic islands.
1. Continental Islands
Continental islands are simply unsubmerged parts of the continental shelf that are entirely surrounded by water. They are connected to the continental shelf. There is water between the mainland and the island. Many of the larger islands of the world are of the continental type. For example, Great Britain is a continental island because it is connected to Europe's continental shelf. In this example, Europe is the mainland and Great Britain is the island! Some other examples of continental islands are Borneo, Java, Sumatra, Sakhalin, Taiwan, and Hainan off Asia, New Guinea, Tasmania, and Kangaroo Island off Australia, Ireland, and Sicily off Europe, Greenland, Newfoundland, Long Island, and Sable Island off North America, and Barbados, Falklands and Trinidad off South America. The islands in rivers and lakes are also continental islands. The city of Paris, France, began as a settlement on an island in the Seine River.
A special type of continental island is the Microcontinental Island, which is created when a large continental island is broken off the main continental shelf but still associated with the continent. Examples are Madagascar and Socotra off Africa, the Kerguelen Islands, New Caledonia, New Zealand, and some of Seychelles.
2. Tidal island
A tidal island refers to a piece of land that becomes visible at low tide but is submerged during high tide. The existence of a tidal island depends on tidal action. The famous island of Mont Saint-Michel, France is an example of a tidal island.
3. Oceanic islands
Oceanic islands or volcanic islands are those that rise to the surface from the floors of the ocean basins. They don't sit on a continental shelf. Many oceanic islands are formed by undersea volcanoes like Hawaii in the Pacific Ocean. An oceanic island forms when a volcano erupts deep under the ocean and pushes the ocean floor upward into a mountain. The island is at the top of that mountain. Unlike continental islands, oceanic islands grow from oceanic crust. Oceanic islands are not scattered haphazardly about the deep ocean waters but are aligned along tectonic plate boundaries where the crust is being created or subducted.
4. Barrier islands
These occur in shallow water and are accumulations of sand deposited by sea currents on the continental shelf. These form 15% of all coastline in the world, including most of the coastline of the continental United States and Alaska, and also occur off the shores of bays and the Great Lakes. They are called barrier islands because they act as barriers between the ocean and the mainland. They protect the coast from being eroded by storm waves and winds. Some barrier islands are stable enough to support houses or an airport runway; others are short-lived, moved annually by winter storms, and re-established by wave and tidal action.
5. Coral islands
They are distinct from both continental islands and oceanic islands in that they are formed of once-living creatures, the corals, which colonize in place to form coral reefs.
An atoll is an island formed from a coral reef that has grown on an eroded and submerged volcanic island. The reef rises to the surface of the water and forms an island. Atolls are typically ring-shaped with a central lagoon. Examples of atolls are the Line Islands in the Pacific and the Maldives in the Indian Ocean.
6. Artificial islands
Some islands are manmade or artificial. One example of this is the island in Osaka Bay off the Japanese island of Honshu on which Kansai International Airport is located.
An archipelago is a group of islands. The islands in archipelagoes may be oceanic or continental. Japan and the Aleutian Islands in Alaska are archipelagoes. Indonesia is the largest archipelago in the world.
The number of species found on an island is determined by two main factors which influence the extinction rate and immigration level of the species.
Islands closer to the mainland are more likely to receive immigrants from the mainland than those farther away from the mainland. This is the 'distance effect'.
The 'size effect' reflects a long-known relationship between island size and species diversity. On smaller islands, the chance of extinction is greater than on larger ones.
Thus, larger islands hold more mammal species than smaller islands, while islands farther away from a given mainland exhibit fewer mammal species than islands closer to the mainland.
