The weirdness of geography: How were islands born?

Islands are often called the "pearls" of the Earth, because it brings a lot of benefits to people, from places where they can be settled to places where they can be docks and landing places. airplanes, maybe even a place to build military bases.

Distinguish the types of islands in the world

In the vast ocean, a land emerges among the blue waves, and when noticed by humans, they can become places to park and replenish ships, planes can land, build new buildings. resort facilities. These 'pearls' are found everywhere on Earth in an ingenious way, and bring many benefits to humans.

So how did the islands come to be? In fact, based on our current understanding, islands are divided into four types: mainland islands (or continental islands), volcanic islands, atolls and alluvial islands.

First type: mainland island

A continental island is a part of land lying on the continental shelf of a certain continent, for example: On the continental shelf of Europe, there are Great Britain, Ireland, and Sicily; Located on the continental shelf of the Americas is the island of Greenland; Located on the Asian continental shelf, there are Sumatra and Kalimantan islands.

A mainland island is a raised island extending from the mainland to the ocean. The largest islands in the world are basically mainland islands. It was created for three reasons:

One is the movement of the Earth's crust so that the junction between it and the mainland collapses into a strait, and the land that was originally connected to the mainland is separated by the sea and becomes an island. Greenland and Ireland, Kalimantan, Madagascar and the world's largest islands, the Japanese archipelago, the British Isles, the Malay Archipelago and other archipelagos such as Taiwan and Hainan were all formed in this way.

The second is the island formed by moraine. During the ancient glacial period, the activity of glaciers carried a large amount of debris and sediment that accumulated downstream, later, as the climate warmed, the glaciers melted, sea levels As it rises, the unsubmerged moraine deposits will become islands. The small islands off the coast of Norway, the Baltic Sea, the eastern border of the United States and Canada were formed in this way.

The third is sea erosion of the island. It is very close to the mainland, and the two are about the same elevation, separated by only a narrow strait; This strait is the result of wave erosion over the years. Such islands are few in number and small in size.

The second type: Volcanic Island

Volcanic islands are islands formed by volcanic activity, erupting lava. Massive amounts of lava were spewed up, then cooled down, forming islands.

It is the exposed part of an underwater volcano. This island has a splendid appearance, which is clearly different from the mainland islands and atolls. At first, the volcano was submerged under water, but after continuous eruptions, magma gradually accumulated and eventually rose out of the water.

Mauna Kea is an island, and is also the highest peak of the submarine volcano range in Hawaii, with its altitude 4,205 meters above sea level and the underwater part is 5,998 meters, its total height is 10,203 meters. Iceland, the eighteenth largest island in the world with an area of ​​​​103,000 square kilometers, was formed by the eruption of thousands of underground volcanoes. The Hawaiian Islands were also actually formed by a series of underwater volcanic eruptions. The Aleutian Islands are arranged in an arc, also formed by the eruption of a series of annular underground volcanoes.

The third type: Atoll

Atolls exist only in tropical and subtropical seas, and are made up of coral skeletons and coral-related organisms. This type of island is often found in shallow sea areas or around volcanic islands.

Under the right conditions, it takes 1,000 years for the atoll to grow 36 meters high, and it will stop growing when it reaches the high tidal currents of the sea. Then, special geological changes will cause these islands to rise above the water and become islands.

The area of ​​coral reefs in the world today is 27 million square kilometers, equivalent to the combined area of ​​Europe and South America, but most of them are underwater.

The Caroline Islands and the Marshall Islands in the Pacific Ocean, the Maldives in the Indian Ocean. are all typical atolls.

Fourth type: Alluvial island

An alluvial island is usually located at the outlet of a large river or on the outer edge of a delta coast, and is a new land formed by the accumulation of river sediments or ocean currents.

The largest alluvial island in the world is Marajo Island, located at the mouth of the Amazon River, the largest river in the world, with an area of ​​​​400,000 square kilometers, ranked as the 30th largest island in the world. Chongming Island and Changxing Island at the mouth of the Yangtze River in China and isolated islands at the mouth of the Yellow River are alluvial islands. Sable Island on the east coast of Canada, Cape Trass on the east coast of the United States and the North Jiangsu sandbar in China are all sandbars formed by the accumulation of ocean currents and winds. With small alluvial islands, their location and size are often not fixed, often changing with the seasons. The most typical example for us to imagine is the alluvial plains in the middle of the Red River.

Other types of islands

In addition to the above 4 types of islands formed by nature, humans have also used modern science and technology to build artificial islands. Such islands are few in number and small in size, but they have great economic significance and great prospects. In the future, we will get rid of sand islands, build giant steel floating hulls, and build factories, galleries, parks, hotels, and even open sea cities. significantly expands the basis for human activities.