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What is a mountain?A mountain is a landform that extends above the surrounding terrain in a limited area. A mountain is
generally steeper than a hill, but there is no universally accepted standard definition for the height of a
mountain or a hill although a mountain usually has an identifiable summit. Mountains cover 54% of Asia, 36%
of North America, 25% of Europe, 22% of South America, 17% of Australia, and 3% of Africa. As a whole, 24% of the Earth's land mass is mountainous. Also, 1 in 10 people live in mountainous regions. Most
of the world's rivers are fed from mountain sources, and more than half of humanity depends on mountains
for water.
Websitehttp://en.wikipedia.org/wiki/Mountain
What is a valley?
In geology, a valley is a depression with predominant extent in one direction. A very deep river valley may be called a canyon or gorge.
The terms U-shaped and V-shaped are descriptive terms of geography to characterize the form of valleys. Most valleys belong to one of these two main types or a mixture of them, at least with respect of the cross section of the slopes or hillsides.
http://en.wikipedia.org/wiki/Valley
What is a canyon?
A canyon (rarely cañon) or gorge is a deep valley between cliffs often carved from the landscape by a river. Most canyons were formed by a process of long-time erosion from a plateau level. The cliffs form because harder rock strata that are resistant to erosion and weathering remain exposed on the valley walls. Canyons are much more common in arid areas than in wetter areas because weathering has a lesser effect in arid zones. Canyon walls are often formed of resistant sandstones or granite. Canyons often form in areas of limestone rock. Limestone is to a certain extent soluble, so cave systems form in the rock. When these collapse a canyon is left.
http://en.wikipedia.org/wiki/Canyon
What is a plateau?
In geology and earth science, A plateau, also called a high plateau or tableland, is an area of highland (any mountainous region or elevated mountainous plateau), usually consisting of relatively flat rural area.
http://en.wikipedia.org/wiki/Plateau
What is a plain?
In geography, a plain is a large area of land with relatively low relief. Plains may be more suitable for farming than plateaus or mountains. Plains are sometimes remnants of much larger features that are now largely eroded, such as mountains or volcanoes.
http://en.wikipedia.org/wiki/Plain
