Earth’s topography is made up of many different types of landforms. While the planet is covered primarily with water, the three major types of landforms are mountains, plains and plateaus. These can be formed by a variety of natural forces, including erosion from water and wind, plate movement, folding and faulting, and volcanic activity.
The most common type of mountains are formed where the Earth’s crust experienced folding or faulting, such as the Canadian Rockies and the Alps. Fault-block mountains were formed when Earth’s crust cracked and was pushed upward. This type of mountain is found in the Sierra Nevada Range. Volcanic mountains form when hot magma from deep in Earth's interior breaks through the crust and builds up on the surface. Volcanism can form islands, such as Hawaii. On land, some of these volcanic mountains appear totally isolated, such as Mount Rainier in Washington State.
Most of the Earth's surface consists of low and high plains, which include prairies, grasslands and steppes. The low plains usually contain sediment deposits due to their low elevation. The high plains, which can have an elevation up to 600 meters, are more influenced by wind erosion. These landforms include the Atlantic Coastal Plain, Gulf Coastal Plain and large interior plains, such as the Great Plains of the United States and Africa.
Plateaus are flat areas that reach higher than high plains, but not as high as mountain ranges. Some plateaus are remnants of very old mountains that have eroded over time, while others have been formed by block-faulting. Plateaus can also be sculpted by wind and rain into mesas, buttes and canyons, such as Monument Valley in the Colorado Plateau. Earth’s largest plateau is the Tibetan Plateau in East Asia.
Valleys, Canyons and Caves
Glaciers, which moved across Earth’s surface and then resided, formed U-shaped valleys. The Finger Lakes in New York State were also formed by glaciers. Canyons and V-shaped valleys are formed by the movement of running water. A river’s gradient defines the steepness and width of the valley it forms. Mountain valleys tend to have steep walls and narrow channels, while valleys on plains have shallow slopes and wider channels. Caves form in karsts, where limestone, dolomite, or gypsum rocks are slowly dissolved by groundwater. Others are formed by waves pounding cliffs on the coastlines, or where molten rock drains out the inside of a lava tube of a volcano.
Many natural factors are responsible for the creation of deserts, particularly current and past climatic conditions. The Mojave Desert in California consists of 1.6 million acres of landscapes that changed over millions of years, including mountains, canyons, volcanic fields and dry lake basins. The region is within a great inland drainage basin where ancient lakes overflowed into adjacent valleys and eventually spilled into Death Valley. After the region dried up, it left dry lake beds exposed to erosion by the wind.
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