An island is a naturally formed land that is scattered in oceans, rivers or lakes and is surrounded by water and emerges from the water at high tide. If two or more islands are concentrated in a small area, they are called "island groups", and the archipelagos arranged in columns are called "islands". And if all the territory of a country is located on an island, then the country is called an island country.

There are tens of thousands of islands in the world's oceans, but there is no precise statistics on how many there are. The standards of islands vary from country to country. Some countries have never announced the number of islands, and it is difficult to accurately count the number of islands.

Islands can be divided into: Continental, volcanic, coral and sedimentary islands .

1.Mainland Island

A mainland island is an area that extends from the mainland to the ocean Due to crustal movement, plate movement, etc. The earth's crust undergoes relative rising and sinking movements Among them, the relatively rising, high-altitude outcropping islands Due to the influence of crustal movement, the area is relatively large Most of the large-scale islands in the world are mainland islands, such as: Greenland, Taiwan, Newfoundland, etc.

2.Volcanic Island

Volcanic island refers to the continuous eruption of submarine volcanoes As the magma cools, it keeps accumulating, getting higher and higher islands that eventually rise above the water due to volcanic eruption Therefore, the terrain of volcanic islands is often more rugged. Volcanic islands are either single or archipelagic Famous volcanic islands include the Aleutian Islands, the Hawaiian Islands, etc.

3.Alluvial island

Alluvial island refers to the estuary of large rivers in the sea Due to the jacking effect of seawater Sediment carried by rivers is deposited in certain areas Islands formed by stacking out of the sea, so they are also called sedimentary islands Alluvial islands are the same as coral islands The island is often low and flat, and the altitude is not high. The location of the sedimentary island is at the mouth of the big river For example, Chongming Island in my country.

4.Coral Island

Coral island refers to the ocean Remains of living corals pile up islands that eventually emerged from the water Because the growth of corals is extremely slow Therefore, the formation of coral islands takes a long time And coral islands will only form in Tropical sea areas suitable for coral growth (mainly in the South Pacific and Indian Ocean) The coral island is very low in altitude, and some are only one or two meters above the sea. The world famous coral island archipelagos are: Maldives Islands, Nansha Islands, Australia's Great Barrier Reef, etc.

Different islands have different shapes. If you are interested in islands, you can analyze the reasons.