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|Dátum: 2011-12-11||Küldd tovább|
America lies on the Northern, Southern and Western hemisphere of the Earth. Asia lies the closest to it at the Bering Strait.
The two main parts are North America and South America which are joined by the narrow isthmus of Central America.
The huge North-Southern extension of America is shown by the fact that it is crossed by the Northern Polar Circle, the Tropic of Cancer, the Equator and by the Tropic of Capricorn. The Southernmost part of the continent lies close to the Southern polar circle.
The continent is bordered by the Arctic Ocean (North), the Atlantic Ocean (East) and by the Pacific Ocean on the West. The two oceans are connected under the narrow Southern part of the continent. Due to the fact that they lie extremely close to each other at Central America, the Panama Canal was built at the narrowest part of the isthmus.
East from Central America, the archipelago of the Caribbean Sea is located with the Lesser Antilles, the Greater Antilles and the Bahamas.
Because of the numerous peninsulas, islands and gulfs the coastline is said to be indented.
Greenland, the greatest island of the world, belongs to the islands of the Arctic Ocean. The islands of the Eastern part: Florida and the Labrador Peninsula. On the West, we can find Alaska and California which run out far into the sea.
The two largest gulfs are the Hudson Bay and the Gulf of Mexico.
The coastline of South America is unindented.
America is the second largest continent after Asia in size: 42.1 million km2.
The relief of land and the mineral resources of North America
The oldest part of it is the Canadian Shield which embraces the Hudson Bay. Towards the West and South-west the shield can also be found under the sediments of the neighbouring regions. It is actually built up of granite and has been created by destruction which consumed many hundred millions of years. That is why its minerals are close to the surface now. Its current surface got created thanks to the Ice age. The ice cap planed its surface by its sliding motion. The soft rocks were excavated, the harder ones were smoothed and the debris was deposited. After the continuous melting of the ice cap the continent started to elevate. The basins were filled up by lakes and the rivers also contributed to the further creation of the relief of North America.
The Appalachians, which lie on the Eastern side of the continent, elevated in the Paleozoic. Between the ranges of the block mountains, there are fertile plateaux and river valleys. On the terraced slopes rivers flow with several waterfalls. Their powers are utilized by hydroelectric power plants. The most important mineral resource is the black coal.
The youngest and the highest mountains of the continent are the Cordilleras and they got created in the tertiary period as a part of the Pacific mountain system. The orogenesis still hasn’t come to and end due to the closing Pacific plate and North American plate. An obvious proof of this was the eruption of Mount St. Helens in 1980.
The ridges of the Pacific mountain system can also be found in South America and even in Asia on the coasts of the Pacific Ocean.
The Western ridges of the Cordilleras are young mountains that are separated by trenches.
The innermost arch of the Cordilleras are the Rocky Mountains which blocks have been arised by Pacific movements again. Its ice-capped peaks make the mountain similar to mountain chains.
The ranges of the Cordilleras embrace several plateaux, such as the Colombian Plateau, the Colorado Plateau and the Mexican plateau.
On the area of Central America the ranges continue with frequent earthquakes and volcanic eruptions.
On the slopes of The Rockies can be located the tables of the Preri which is covered by loess.
The lowest and youngest region of North America is the Mississippi Plain. Once it was flooded by the ocean. Its horizontally deposited layers of sediments hide oil and natural gas. On the thick layers the Mississippi and its tributaries deposited debris.
The relief of land and the mineral resources of North America
South America has two shields: The Guyana shield and the Brazil Highland. Both were parts of the Gondvanaland on the Southern hemisphere. Their pieces, which are connected deeply under the land, are actually connected by the Amazonas Basin on the surface which is mainly built up of the sediments of the sea and deposits.
The ridges of the Western part of the continent elevated because of the folding of the oceanic and the continental plate. The deposits of the oceanic plate and the rocks of the plate themselves went deep and melted, and intensive volcanic activity started: this is how the volcanic ridges were formed. The folded sediments elevated on the Eastern part.
The Andes, which are the longest mountain chains all over the world, formed in this way as part of the Pacific mountain system. In front of it, under the Pacific Ocean, there is a trench because it is a subduction zone where the oceanic plate goes under the continental plate.
This process, which started in the Mesozoic, has not yet come to an end. Because of the colliding plates, volcanic activities and earthquakes are still very frequent. The Southern part of the Andes is the second in the row of the most seizmic parts of the Earth after Japan.
The Andes have many magmatic rocks – such as the andesite which name is similar to the name of the mountain itself.
Over and above the factors mentioned above – because of the height above sea level -, the surface was formed by the ice as well.
The ranges are North-Southern in orientation. They surround plateaus. The greatest one of them is the Bolivian Plateau which is covered by a thick layer of debris and lava.
The mineral resources of the Andes got close to the surface during volcanic activities and they are ores of non-ferrous metals and precious metals such as copper, tin-stone and silver.
The youngest regions of the continent are the plains. The plain of the Northern part of South America is the Orinoco Basin which is rich in oil. The Parana Plain is located on the Southern part of the continent. In the basin of the Amazon River not only the largest plain of the continent but that of the Earth is lying as well. In the Tertiary period there was a gulf but the accumulation of the debris of the Amazon River created a plain on the area of it. Its slope faces the Atlantic Ocean.
Last but not least, we have to mention Patagonia which is built up of tables and on which the accumulated volcanic debris and the debris of the glaciers are originated from the Andes.