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A mountain is an elevated portion of the
Earth's crust Earth's crust is Earth's thin outer shell of rock, referring to less than 1% of Earth's radius and volume. It is the top component of the lithosphere, a division of Earth's layers that includes the crust and the upper part of the mantle. The ...
, generally with steep sides that show significant exposed
bedrock In geology, bedrock is solid Rock (geology), rock that lies under loose material (regolith) within the crust (geology), crust of Earth or another terrestrial planet. Definition Bedrock is the solid rock that underlies looser surface mater ...
. Although definitions vary, a mountain may differ from a plateau in having a limited
summit A summit is a point on a surface that is higher in elevation than all points immediately adjacent to it. The topography, topographic terms acme, apex, peak (mountain peak), and zenith are synonymous. The term (mountain top) is generally used ...
area, and is usually higher than a hill, typically rising at least 300 metres (1,000 feet) above the surrounding land. A few mountains are isolated summits, but most occur in mountain ranges. Mountains are formed through tectonic forces, erosion, or volcanism, which act on time scales of up to tens of millions of years. Once mountain building ceases, mountains are slowly leveled through the action of weathering, through
slumping Slumping is a technique in which items are made in a kiln by means of shaping glass over molds at high temperatures. The slumping of a pyrometric cone is often used to measure temperature in a kiln. Technique Slumping glass is a highly techni ...
and other forms of mass wasting, as well as through erosion by rivers and glaciers. High elevations on mountains produce colder climates than at sea level at similar latitude. These colder climates strongly affect the ecosystems of mountains: different elevations have different plants and animals. 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 Logging is the process of cutting, processing, and moving trees to a location for transport. It may include skidding, on-site processing, and loading of trees or logs onto trucks or skeleton cars. Logging is the beginning of a supply chain ...
, along with recreation, such as
mountain climbing Mountaineering or alpinism, is a set of outdoor activities that involves ascending tall mountains. Mountaineering-related activities include traditional outdoor climbing, skiing, and traversing via ferratas. Indoor climbing, sport climbing, a ...
and skiing. The highest mountain on Earth is Mount Everest in the Himalayas of Asia, whose summit is above mean sea level. The highest known mountain on any planet in the Solar System is
Olympus Mons Olympus Mons (; Latin for Mount Olympus) is a large shield volcano on Mars. The volcano has a height of over 21.9 km (13.6 mi or 72,000 ft) as measured by the Mars Orbiter Laser Altimeter (MOLA). Olympus Mons is about two and a h ...
on Mars at .


Definition

There is no universally accepted definition of a mountain. Elevation, volume, relief, steepness, spacing and continuity have been used as criteria for defining a mountain. 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." Whether a landform is called a mountain may depend on local usage. Mount Scott outside
Lawton, Oklahoma Lawton is a city in and the county seat of Comanche County, in the U.S. state of Oklahoma Oklahoma (; Choctaw language, Choctaw: ; chr, ᎣᎧᎳᎰᎹ, ''Okalahoma'' ) is a U.S. state, state in the South Central United States, South Ce ...
, US, is only from its base to its highest point. John Whittow's ''Dictionary of Physical Geography'' states "Some authorities regard eminences above as mountains, those below being referred to as hills." In the United Kingdom and the Republic of Ireland, a mountain is usually defined as any summit at least high, which accords with the official UK government's definition that a mountain, for the purposes of access, is a summit of or higher. In addition, some definitions also include a topographical prominence requirement, such as that the mountain rises above the surrounding terrain. At one time the US Board on Geographic Names defined a mountain as being or taller, but has abandoned the definition since the 1970s. Any similar landform lower than this height was considered a hill. However, today, the US Geological Survey concludes that these terms do not have technical definitions in the US. The
UN Environmental Programme The United Nations Environment Programme (UNEP) is responsible for coordinating responses to environmental issues within the United Nations system. It was established by Maurice Strong, its first director, after the Declaration of the United Natio ...
's definition of "mountainous environment" includes any of the following: * Class 1: Elevation greater than . * Class 2: Elevation between and . * Class 3: Elevation between and . * Class 4: Elevation between and , with a slope greater than 2 degrees. * Class 5: Elevation between and , with a slope greater than 5 degrees and/or elevation range within . * Class 6: Elevation between and , with a elevation range within . * Class 7: Isolated inner basins and plateaus less than in area that are completely surrounded by Class 1 to 6 mountains, but do not themselves meet criteria for Class 1 to 6 mountains. Using these definitions, mountains cover 33% of Eurasia, 19% of South America, 24% of North America, and 14% of Africa. As a whole, 24% of the Earth's land mass is mountainous.


Geology

There are three main types of mountains: volcanic,
fold Fold, folding or foldable may refer to: Arts, entertainment, and media * ''Fold'' (album), the debut release by Australian rock band Epicure *Fold (poker), in the game of poker, to discard one's hand and forfeit interest in the current pot *Above ...
, and block. All three types are formed from plate tectonics: when portions of the Earth's crust move, crumple, and dive. Compressional forces, isostatic
uplift Uplift may refer to: Science * Geologic uplift, a geological process ** Tectonic uplift, a geological process * Stellar uplift, the theoretical prospect of moving a stellar mass * Uplift mountains * Llano Uplift * Nemaha Uplift Business * Uplif ...
and intrusion of igneous matter forces surface rock upward, creating a landform higher than the surrounding features. The height of the feature makes it either a hill or, if higher and steeper, a mountain. Major mountains tend to occur in long linear arcs, indicating tectonic plate boundaries and activity.


Volcanoes

Volcanoes are formed when a plate is pushed below another plate, or at a mid-ocean ridge or
hotspot Hotspot, Hot Spot or Hot spot may refer to: Places * Hot Spot, Kentucky, a community in the United States Arts, entertainment, and media Fictional entities * Hot Spot (comics), a name for the DC Comics character Isaiah Crockett * Hot Spot (Tra ...
. At a depth of around , melting occurs in rock above the slab (due to the addition of water), and forms magma that reaches the surface. When the magma reaches the surface, it often builds a volcanic mountain, such as a
shield volcano A shield volcano is a type of volcano named for its low profile, resembling a warrior's shield lying on the ground. It is formed by the eruption of highly fluid (low viscosity) lava, which travels farther and forms thinner flows than the more v ...
or a
stratovolcano A stratovolcano, also known as a composite volcano, is a conical volcano built up by many layers (strata) of hardened lava and tephra. Unlike shield volcanoes, stratovolcanoes are characterized by a steep profile with a summit crater and per ...
. Examples of volcanoes include
Mount Fuji , or Fugaku, located on the island of Honshū, is the highest mountain in Japan, with a summit elevation of . It is the second-highest volcano located on an island in Asia (after Mount Kerinci on the island of Sumatra), and seventh-highest p ...
in Japan and Mount Pinatubo in the Philippines. The magma does not have to reach the surface in order to create a mountain: magma that solidifies below ground can still form dome mountains, such as Navajo Mountain in the US.


Fold mountains

Fold mountains occur when two plates collide: shortening occurs along thrust faults and the crust is overthickened. Since the less dense continental crust "floats" on the denser
mantle A mantle is a piece of clothing, a type of cloak. Several other meanings are derived from that. Mantle may refer to: *Mantle (clothing), a cloak-like garment worn mainly by women as fashionable outerwear **Mantle (vesture), an Eastern Orthodox ve ...
rocks beneath, the weight of any crustal material forced upward to form hills, plateaus or mountains must be balanced by the buoyancy force of a much greater volume forced downward into the mantle. Thus the continental crust is normally much thicker under mountains, compared to lower lying areas. Rock can
fold Fold, folding or foldable may refer to: Arts, entertainment, and media * ''Fold'' (album), the debut release by Australian rock band Epicure *Fold (poker), in the game of poker, to discard one's hand and forfeit interest in the current pot *Above ...
either symmetrically or asymmetrically. The upfolds are anticlines and the downfolds are
syncline In structural geology, a syncline is a fold with younger layers closer to the center of the structure, whereas an anticline is the inverse of a syncline. A synclinorium (plural synclinoriums or synclinoria) is a large syncline with superimpose ...
s: in asymmetric folding there may also be recumbent and overturned folds. The
Balkan Mountains The Balkan mountain range (, , known locally also as Stara planina) is a mountain range in the eastern part of the Balkan Peninsula in Southeastern Europe. The range is conventionally taken to begin at the peak of Vrashka Chuka on the border betw ...
and the
Jura Mountains The Jura Mountains ( , , , ; french: Massif du Jura; german: Juragebirge; it, Massiccio del Giura, rm, Montagnas da Jura) are a sub-alpine mountain range a short distance north of the Western Alps and mainly demarcate a long part of the Frenc ...
are examples of fold mountains.


Block mountains

Block mountains are caused by faults in the crust: a plane where rocks have moved past each other. When rocks on one side of a fault rise relative to the other, it can form a mountain. The uplifted blocks are block mountains or horsts. The intervening dropped blocks are termed
graben In geology, a graben () is a depressed block of the crust of a planet or moon, bordered by parallel normal faults. Etymology ''Graben'' is a loan word from German, meaning 'ditch' or 'trench'. The word was first used in the geologic contex ...
: these can be small or form extensive rift valley systems. This form of
landscape A landscape is the visible features of an area of land, its landforms, and how they integrate with natural or man-made features, often considered in terms of their aesthetic appeal.''New Oxford American Dictionary''. A landscape includes the ...
can be seen in
East Africa East Africa, Eastern Africa, or East of Africa, is the eastern subregion of the African continent. In the United Nations Statistics Division scheme of geographic regions, 10-11-(16*) territories make up Eastern Africa: Due to the historical ...
, the Vosges and Rhine valley, and the Basin and Range Province of Western North America. These areas often occur when the regional stress is extensional and the crust is thinned.


Erosion

During and following uplift, mountains are subjected to the agents of erosion (water, wind, ice, and gravity) which gradually wear the uplifted area down. Erosion causes the surface of mountains to be younger than the rocks that form the mountains themselves. Glacial processes produce characteristic landforms, such as pyramidal peaks, knife-edge arêtes, and bowl-shaped
cirque A (; from the Latin word ') is an amphitheatre-like valley formed by glacial erosion. Alternative names for this landform are corrie (from Scottish Gaelic , meaning a pot or cauldron) and (; ). A cirque may also be a similarly shaped landform ...
s that can contain lakes. Plateau mountains, such as the Catskills, are formed from the erosion of an uplifted plateau.


Climate

Climate in the mountains becomes colder at high elevations, due to an interaction between
radiation In physics, radiation is the emission or transmission of energy in the form of waves or particles through space or through a material medium. This includes: * ''electromagnetic radiation'', such as radio waves, microwaves, infrared, visi ...
and convection. Sunlight in the visible spectrum hits the ground and heats it. The ground then heats the air at the surface. If radiation were the only way to transfer heat from the ground to space, the greenhouse effect of gases in the atmosphere would keep the ground at roughly , and the temperature would decay exponentially with height. However, when air is hot, it tends to expand, which lowers its density. Thus, hot air tends to rise and transfer heat upward. This is the process of convection. Convection comes to equilibrium when a parcel of air at a given altitude has the same density as its surroundings. Air is a poor conductor of heat, so a parcel of air will rise and fall without exchanging heat. This is known as an adiabatic process, which has a characteristic pressure-temperature dependence. As the pressure gets lower, the temperature decreases. The rate of decrease of temperature with elevation is known as the adiabatic lapse rate, which is approximately 9.8 °C per kilometre (or per 1000 feet) of altitude. The presence of water in the atmosphere complicates the process of convection. Water vapor contains latent
heat of vaporization The enthalpy of vaporization (symbol ), also known as the (latent) heat of vaporization or heat of evaporation, is the amount of energy (enthalpy) that must be added to a liquid substance to transform a quantity of that substance into a gas. T ...
. As air rises and cools, it eventually becomes saturated and cannot hold its quantity of water vapor. The water vapor condenses (forming clouds), and releases heat, which changes the lapse rate from the dry adiabatic lapse rate to the moist adiabatic lapse rate (5.5 °C per kilometre or per 1000 feet) The actual lapse rate can vary by altitude and by location. Therefore, moving up on a mountain is roughly equivalent to moving 80 kilometres (45 miles or 0.75° of latitude) towards the nearest pole. This relationship is only approximate, however, since local factors such as proximity to oceans (such as the Arctic Ocean) can drastically modify the climate. As the altitude increases, the main form of precipitation becomes snow and the winds increase. The effect of the climate on the ecology at an elevation can be largely captured through a combination of amount of precipitation, and the
biotemperature The Holdridge life zones system is a global bioclimatic scheme for the classification of land areas. It was first published by Leslie Holdridge in 1947, and updated in 1967. It is a relatively simple system based on few empirical data, giving obj ...
, as described by Leslie Holdridge in 1947. Biotemperature is the mean temperature; all temperatures below are considered to be 0 °C. When the temperature is below 0 °C, plants are
dormant Dormant, "sleeping", may refer to: Science *Dormancy Dormancy is a period in an organism's life cycle when growth, development, and (in animals) physical activity are temporarily stopped. This minimizes metabolic activity and therefore helps ...
, so the exact temperature is unimportant. The peaks of mountains with permanent snow can have a biotemperature below .


Climate change

Mountain environments are particularly sensitive to anthropogenic climate change and are currently undergoing alterations unprecedented in last 10,000 years. In recent decades mountain ice caps and glaciers have experienced accelerating ice loss. The melting of the glaciers, permafrost and snow has caused underlying surfaces to become increasingly unstable. Landslip hazards have increased in both number and magnitude due to climate change. Alpine ecosystems can also thus be particularly climatically sensitive. Many mid-latitude mountains act as cold climate refugia, with the ecosystems occupying small environmental niches. As well as the direct influence that the change in climate can have on an ecosystem, there is also the indirect one on the soils from changes in stability and soil development. Patterns of river discharge are also significantly affected by climate change, which in turn has significant impacts on communities that rely on water fed from alpine sources. Nearly half of mountain areas provide essential or supportive water resources for mainly urban populations, in particular during the dry season and in semiarid areas such as in central Asia.


Ecology

The colder climate on mountains affects the plants and animals residing on mountains. A particular set of plants and animals tend to be adapted to a relatively narrow range of climate. Thus, ecosystems tend to lie along elevation bands of roughly constant climate. This is called altitudinal zonation. In regions with dry climates, the tendency of mountains to have higher precipitation as well as lower temperatures also provides for varying conditions, which enhances zonation. Some plants and animals found in altitudinal zones tend to become isolated since the conditions above and below a particular zone will be inhospitable and thus constrain their movements or dispersal. These isolated ecological systems are known as sky islands. Altitudinal zones tend to follow a typical pattern. At the highest elevations, trees cannot grow, and whatever life may be present will be of the alpine type, resembling tundra. Just below the tree line, one may find subalpine forests of needleleaf trees, which can withstand cold, dry conditions. Below that, montane forests grow. In the temperate portions of the earth, those forests tend to be needleleaf trees, while in the tropics, they can be
broadleaf tree A broad-leaved, broad-leaf, or broadleaf tree is any tree within the diverse botanical group of angiosperms that has flat leaves and produces seeds inside of fruits. It is one of two general types of trees, the other being a conifer, a tree with ne ...
s growing in a rain forest.


Mountains and humans

The highest known permanently tolerable altitude is at . At very high altitudes, the decreasing atmospheric pressure means that less oxygen is available for breathing, and there is less protection against solar radiation ( UV). Above elevation, there is not enough oxygen to support human life. This is sometimes referred to as the " death zone". The summits of Mount Everest and K2 are in the death zone.


Mountain societies and economies

Mountains are generally less preferable for human habitation than lowlands, because of harsh weather and little level ground suitable for agriculture. While 7% of the land area of Earth is above , only 140 million people live above that altitude and only 20-30 million people above elevation. About half of mountain dwellers live in the Andes, Central Asia, and Africa. With limited access to infrastructure, only a handful of human communities exist above of elevation. Many are small and have heavily specialized economies, often relying on industries such as agriculture, mining, and tourism. An example of such a specialized town is La Rinconada, Peru, a gold-mining town and the highest elevation human habitation at . A counterexample is El Alto,
Bolivia , image_flag = Bandera de Bolivia (Estado).svg , flag_alt = Horizontal tricolor (red, yellow, and green from top to bottom) with the coat of arms of Bolivia in the center , flag_alt2 = 7 × 7 square p ...
, at , which has a highly diverse service and manufacturing economy and a population of nearly 1 million. Traditional mountain societies rely on agriculture, with higher risk of crop failure than at lower elevations. Minerals often occur in mountains, with mining being an important component of the economics of some montane societies. More recently, tourism supports mountain communities, with some intensive development around attractions such as
national park A national park is a nature park, natural park in use for conservation (ethic), conservation purposes, created and protected by national governments. Often it is a reserve of natural, semi-natural, or developed land that a sovereign state dec ...
s or ski resorts. About 80% of mountain people live below the poverty line. Most of the world's rivers are fed from mountain sources, with snow acting as a storage mechanism for downstream users. More than half of humanity depends on mountains for water. In
geopolitics Geopolitics (from Greek γῆ ''gê'' "earth, land" and πολιτική ''politikḗ'' "politics") is the study of the effects of Earth's geography (human and physical) on politics and international relations. While geopolitics usually refers to ...
mountains are often seen as preferable "
natural boundaries A natural border is a border between Sovereign state, states or their subdivisions which is concomitant with natural formations such as rivers or mountain ranges. The "doctrine of natural boundaries" developed in Western culture in the 18th centu ...
" between polities.


Mountaineering

Mountain climbing, or alpinism is the sport, hobby or profession of hiking, skiing, and climbing mountains. While mountaineering began as attempts to reach the highest point of unclimbed big mountains it has branched into specializations that address different aspects of the mountain and consists of three areas: rock-craft, snow-craft and skiing, depending on whether the route chosen is over rock, snow or ice. All require experience, athletic ability, and technical knowledge of the terrain to maintain safety.


Mountains as sacred places

Mountains often play a significant role in religion. There are for example a number of sacred mountains within Greece such as Mount Olympus which was held to be the home of the gods. In Japanese culture, the 3,776.24 m (12,389 ft) volcano of
Mount Fuji , or Fugaku, located on the island of Honshū, is the highest mountain in Japan, with a summit elevation of . It is the second-highest volcano located on an island in Asia (after Mount Kerinci on the island of Sumatra), and seventh-highest p ...
is also held to be sacred with tens of thousands of Japanese ascending it each year. Mount Kailash, in the Tibet Autonomous Region of China, is considered to be sacred in four religions: Hinduism, Bon, Buddhism, and Jainism. In Ireland, pilgrimages are made up the Mount Brandon by Irish Catholics. The Himalayan peak of Nanda Devi is associated with the
Hindu Hindus (; ) are people who religiously adhere to Hinduism.Jeffery D. Long (2007), A Vision for Hinduism, IB Tauris, , pages 35–37 Historically, the term has also been used as a geographical, cultural, and later religious identifier for ...
goddesses Nanda and Sunanda; it has been off-limits to climbers since 1983. Mount Ararat is a sacred mountain, as it is believed to be the landing place of Noah's Ark. In Europe and especially in the Alps,
summit cross A summit cross (german: Gipfelkreuz) is a cross on the summit of a mountain or hill that marks the top. Often there will be a summit register (''Gipfelbuch'') at the cross, either in a container or at least a weatherproof case. Various other form ...
es are often erected on the tops of prominent mountains.


Superlatives

Heights of mountains are typically measured
above sea level Height above mean sea level is a measure of the vertical distance (height, elevation or altitude) of a location in reference to a historic mean sea level taken as a vertical datum. In geodesy, it is formalized as ''orthometric heights''. The comb ...
. Using this metric, Mount Everest is the highest mountain on Earth, at . There are at least 100 mountains with heights of over
above sea level Height above mean sea level is a measure of the vertical distance (height, elevation or altitude) of a location in reference to a historic mean sea level taken as a vertical datum. In geodesy, it is formalized as ''orthometric heights''. The comb ...
, all of which are located in central and southern Asia. The highest mountains above sea level are generally not the highest above the surrounding terrain. There is no precise definition of surrounding base, but Denali,
Mount Kilimanjaro Mount Kilimanjaro () is a dormant volcano in Tanzania. It has three volcanic cones: Kibo, Mawenzi, and Shira. It is the highest mountain in Africa and the highest free-standing mountain above sea level in the world: above sea level and ab ...
and Nanga Parbat are possible candidates for the tallest mountain on land by this measure. The bases of mountain islands are below sea level, and given this consideration
Mauna Kea Mauna Kea ( or ; ; abbreviation for ''Mauna a Wākea''); is a dormant volcano on the island of Hawaii. Its peak is above sea level, making it the highest point in the state of Hawaii and second-highest peak of an island on Earth. The peak is ...
( above sea level) is the world's tallest mountain and volcano, rising about from the Pacific Ocean floor. The highest mountains are not generally the most voluminous. Mauna Loa () is the largest mountain on Earth in terms of base area (about ) and volume (about ).
Mount Kilimanjaro Mount Kilimanjaro () is a dormant volcano in Tanzania. It has three volcanic cones: Kibo, Mawenzi, and Shira. It is the highest mountain in Africa and the highest free-standing mountain above sea level in the world: above sea level and ab ...
is the largest non-shield volcano in terms of both base area () and volume ().
Mount Logan Mount Logan () is the highest mountain in Canada and the second-highest peak in North America after Denali. The mountain was named after Sir William Edmond Logan, a Canadian geologist and founder of the Geological Survey of Canada (GSC). Mount ...
is the largest non-volcanic mountain in base area (). The highest mountains above sea level are also not those with peaks farthest from the centre of the Earth, because the
figure of the Earth Figure of the Earth is a Jargon, term of art in geodesy that refers to the size and shape used to model Earth. The size and shape it refers to depend on context, including the precision needed for the model. A Spherical Earth, sphere is a well-k ...
is not spherical. Sea level closer to the equator is several miles farther from the centre of the Earth. The summit of Chimborazo, Ecuador's tallest mountain, is usually considered to be the farthest point from the Earth's centre, although the southern summit of Peru's tallest mountain, Huascarán, is another contender. Both have elevations above sea level more than less than that of Everest.


See also

* List of mountain ranges * List of peaks by prominence *
List of ski areas and resorts This is a list of ski areas and resorts around the world. Africa Asia Europe North America See also * Comparison of North American ski resorts * Comparison of California ski resorts See also * Comparison of Colorado ski resorts *Compar ...
* Lists of mountains * * Seven Summits


References

{{Authority control Geography terminology Earth's crust