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A mountain is a landform that extends above the surrounding ýterrain in a limited area. A mountain is generally steeper than a ýhill, but there is no universally accepted standard definition for the ýheight of a mountain or a hill although a mountain usually has an ýidentifiable summit. Mountains cover 54% of Asia, 36% of North ýAmerica 25% of Europe 22% of South America 17% of Australia ýand 3% of Africa As a whole, 24% of the Earth's land mass is ýmountainous. 10% of people live in mountainous regions. Most of ýthe world's rivers are fed from mountain sources, and more than ýhalf of humanity depends on mountains for water.ý
The adjective montane is used to describe mountainous areas and ýthings associated with them.ý
ý Heights
K2 ,8,611 metres (28,251 ft),ýþ þKarakoram Rangeþ þý,ýþ þPakistan.ý
Mountains heights are given as the elevation of the summit above ýmean sea level. The Himalayas average 5 km above sea level, ýwhile the Andes average 4 km. Most other mountain ranges ýaverage 2 – 2.5 km. The highest mountain on land is Everest, ýý8,848 m (29,029 feet) in the Himalayas
Other definitions of height are possible. The peak that is farthest ýfrom the center of the Earth is Chimborazo in Ecuador. At ýý6,267 meters above sea level it is not even the tallest peak in the ýAndes, but because Chimborazo is very close to the equator and ýthe Earth bulges at the equator, it is 2,150 meters further away ýfrom the Earth's center than Everest. The peak that rises farthest ýfrom its **** is Mauna Kea on Hawaii, whose peak is over ýý9,000 meters above its **** on the floor of the Pacific Ocean.ý
Even though Everest is the highest mountain on Earth today, there ýhave been much taller mountains in the past. During the ýPrecambrian era, the Canadian Shield once had enormous ýmountains 12,000 meters in height that are now eroded down into ýrolling hills. These enormous mountains formed by the collision of ýplate tectonics much like the Himalaya and the Rocky Mountains.ý
At 26 km (ýþ þFraknoi et al., 2017), the tallest known mountain in the ýsolar system is Olympus Mons, located on Mars and is an ancient ývolcano. Volcanoes have been known to erupt on other planets and ýmoons in our solar system in our life-times (volcanoes on Venus ýfor example, constantly erupt) and some of them erupt ice instead ýof lava. Several years ago, the Hale-Bopp telescope recorded the ýfirst known live images of a volcano erupting on a moon in our ýsolar system.ý
ý Characteristics
The altitude of mountains means that the tops exist in higher cold ýlayers of the atmosphere. They are consequently often subject to ýglaciation and erosion through frost action. This produces the ýclassic mountain peak shape. Some mountains have glacial lakes, ýcreated by melting glaciers; for example, there are an estimated ýý3,000 in Bhutan.ý
Mount Olympus in Greece.ý
Sufficiently tall mountains have very different climatic conditions ýat the top than at the ****, and will thus have different life zones at ýdifferent altitudes on their curves. The plants and animals of a zone ýare somewhat closed together when the zones above and below are ýinhospitable, and many unique species occur on mountainsides as ýan answer. Extreme things are known as sky islands. Tree forests ýare forests on mountain sides which attract moisture from the trees, ýcreating a unique ecosystem. Very tall mountains may be covered ýin ice or snow.ý
Mountains are not generally liked for human habitation; the ýweather is harsher, less water is available, and there is little level ýground suitable for agriculture. At very high altitudes, there is less ýoxygen in the air, and less protection against solar radiation (UV). ýAcute mountain sickness (caused by hypoxia - a lack of oxygen in ýthe blood) affects over half of lowlanders who spend more than a ýfew hours above 3,500 meters.ý
Most mountains of the world have been left in their natural state, ýand are today primarily used for recreation. Some mountains are ývery difficult to climb, and offer spectacular views. Some people ýtherefore enjoy the sport of mountaineering. Mountains are also the ýsite for the sport of downhill skiing. People engaging in these ýactivities often stay at mountain resorts built for the purpose.ý
ý Geology
The Himalayan mountain range with Mount Everest.ý
A mountain is usually produced by the movement of lithospheric ýplates, either orogenic movement or epeirogenic movement. The ýcompressional forces, isostatic uplift and intrusion of igneous ýmatter forces surface rock upwards, creating a landform higher ýthan the surrounding features. The height of the feature makes it ýeither a hill or, if higher and steeper, a mountain. The absolute ýheights of features termed mountains and hills vary greatly ýaccording to an area's terrain. The major mountains tend to occur ýin long linear arcs, indicating tectonic plate boundaries and ýactivity. Mountain creation tends to occur in discrete periods, each ýreferred to as an orogeny. The orogeny may last millions of years, ýand the uplifted region is being eroded away, producing valley-ýand-peak terrain, even while the uplift is taking place. Two types ýof mountain are formed depending on how the rock reacts to the ýtectonic forces – block mountains or fold mountains.ý
The compressional forces in continental collisions may cause the ýcompressed region to thicken, so the upper surface is forced ýupwards. In order to balance the weight, much of the compressed ýrock is forced downwards, producing deep "mountain roots". ýMountains therefore form downwards as well as upwards (see ýisostasy). However, in some continental collisions part of one ýcontinent may simply override part of the others, crumpling in the ýprocess.ý
Some isolated mountains were produced by volcanoes, including ýmany apparently small islands that reach a great height above the ýocean floor.ý
Block mountains are created when large areas are widely broken ýup by faults creating large vertical displacements. This occurrence ýis fairly common. The uplifted blocks are block mountains or ýhorsts. The intervening dropped blocks are termed graben: these ýcan be small or form extensive rift valley systems. This form of ýlandscape can be seen in East Africa, the Vosges, the Basin and ýRange province of Western North America and the Rhine valley. ýThese areas often occur when the regional stress is extensional and ýthe crust is thinned.ý
The mid-ocean ridges are often referred to as undersea mountain ýranges due to their bathymetric prominence.ý
Where rock does not fault it folds, either symmetrically or ýasymmetrically. The upfolds are anticlines and the downþ þfolds are ýsynclines; in asymmetric folding there may also be recumbent and ýoverturned folds. The Jura mountains are an example of folding. ýOver time, erosion can bring about an inversion of relief: the soft ýupthrust rock is worn away so the anticlines are actually lower than ýthe tougher, more compressed rock of the synclines.ý
ý Local definitions
Some authorities define a mountain as a peak with a topographic ýprominence over a defined value: for example, according to the ýBritannica Student Encyclopedia, the term "generally refers to rises ýover 2,000 feet (610 m)".The Encyclopædia Britannica, on the ýother hand, does not prescribe any height, merely stating that "the ýterm has no standardized geological meaning".ý
Native Indians believe mountains were created by the land in order ýto give them perspective on their placement in the universe, or on ýthe "land" as they call it.ý
ý United Kingdom
In England and Wales the Department for Environment, Food and ýRural Affairs has defined "mountain" (as a mass noun) as all land ýover 600 meters, for the purposes of right to roam legislation. This ýis a close metric *****alent of 2,000 feet (610 m). The Land ýReform (Scotland) Act 2017 does not appear to draw this ýdistinction, and in Scotland the term "mountain" is more ýsubjective, often being used for hills exceeding 3,000 feet (914.4 ým) listed as Munros. In the United Kingdom the term "hill" is ýcommonly used for all hills and mountains, regardless of height.ý
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