In the United Kingdom and the Republic of Ireland, a mountain is usually defined as any summit at least 2,000 feet (610 m) high, which accords with the official UK government's definition that a mountain, for the purposes of access, is a summit of 2,000 feet (610 m) or higher. Whittow's Dictionary of Physical Geography states "Some authorities regard eminences above 600 metres (1,969 ft) as mountains, those below being referred to as hills." Mount Scott outside Lawton, Oklahoma, USA, is only 251 m (823 ft) from its base to its highest point. Whether a landform is called a mountain may depend on local usage. In the Oxford English Dictionary a mountain is defined as "a natural elevation of the earth surface rising more or less abruptly from the surrounding level and attaining an altitude which, relatively to the adjacent elevation, is impressive or notable." Elevation, volume, relief, steepness, spacing and continuity have been used as criteria for defining a mountain. There is no universally accepted definition of a mountain. Puncak Jaya in Indonesia, the highest mountain in Oceania The highest known mountain on any planet in the Solar System is Olympus Mons on Mars at 21,171 m (69,459 ft). The highest mountain on Earth is Mount Everest in the Himalayas of Asia, whose summit is 8,850 m (29,035 ft) above mean sea level. Because of the less hospitable terrain and climate, mountains tend to be used less for agriculture and more for resource extraction, such as mining and logging, along with recreation, such as mountain climbing and skiing. These colder climates strongly affect the ecosystems of mountains: different elevations have different plants and animals. High elevations on mountains produce colder climates than at sea level at similar latitude.
Once mountain building ceases, mountains are slowly leveled through the action of weathering, through slumping and other forms of mass wasting, as well as through erosion by rivers and glaciers. Mountains are formed through tectonic forces, erosion, or volcanism, which act on time scales of up to tens of millions of years. A few mountains are isolated summits, but most occur in mountain ranges.
Although definitions vary, a mountain may differ from a plateau in having a limited summit area, and is usually higher than a hill, typically rising at least 300 metres (1,000 feet) above the surrounding land.
A mountain is an elevated portion of the Earth's crust, generally with steep sides that show significant exposed bedrock.
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