Mountains of the Himalayas


A mountain is an elevated portion of the
Earth's crust Earth's crust is a thin shell on the outside of Earth Earth is the third planet from the Sun and the only astronomical object known to harbour and support life. 29.2% of Earth's surface is land consisting of continents and islands. The ...
, generally with steep sides that show significant exposed
bedrock Bedrock in geology Geology (from the γῆ, ''gē'' ("earth") and -λoγία, ''-logia'', ("study of", "discourse")) is a branch of concerned with both the liquid and , the of which it is composed, and the processes by which they cha ...

. A mountain differs from a
plateau In geology Geology (from the Ancient Greek γῆ, ''gē'' ("earth") and -λoγία, ''-logia'', ("study of", "discourse")) is an Earth science concerned with the solid Earth, the rock (geology), rocks of which it is composed, and the proces ...

in having a limited summit area, and is larger than a
hill A hill is a landform A landform is a natural or artificial feature of the solid surface of the Earth or other planetary body A planet is an astronomical body Astronomy (from el, ἀστρονομία, literally meaning the scie ...

, typically rising at least 300 metres (1000 feet) above the surrounding land. A few mountains are isolated
summits 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 ...
, but most occur in
mountain range A mountain range is a series of mountains ranged in a line and connected by high ground. A mountain system or mountain belt is a group of mountain ranges with similarity in form, structure, and alignment that have arisen from the same cause, us ...

mountain range
s. Mountains are formed through tectonic forces,
erosion In earth science Earth science or geoscience includes all fields of natural science Natural science is a branch of science Science (from the Latin word ''scientia'', meaning "knowledge") is a systematic enterprise that Scientific ...

, or
volcanism Volcanism (or volcanicity) is the phenomenon of eruption of molten rock (magma Magma () is the molten or semi-molten natural material from which all igneous rock Igneous rock (derived from the Latin word ''ignis'' meaning fire), or magma ...
, 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 Weathering is the deterioration of Rock (geology), rocks, soils and minerals as well as wood and artificial materials through contact with water, atmospheric gases, and biological organisms. Weathering occurs ''in situ'' (on site, with little o ...
, through
slumping Slumping is a technique in which items are made in a kiln , Wrecclesham Wrecclesham is a village on the southern outskirts of the large town of Farnham Farnham is a market town in Surrey, England, within the Borough of Waverley Boroug ...
and other forms of
mass wasting Mass wasting, also known as mass movement, is a general term for the movement of rock Rock most often refers to: * Rock (geology) A rock is any naturally occurring solid mass or aggregate of minerals or mineraloid matter. It is categori ...
, as well as through
erosion In earth science Earth science or geoscience includes all fields of natural science Natural science is a branch of science Science (from the Latin word ''scientia'', meaning "knowledge") is a systematic enterprise that Scientific ...

river A river is a natural flowing watercourse, usually freshwater, flowing towards an ocean, sea, lake or another river. In some cases, a river flows into the ground and becomes dry at the end of its course without reaching another body of wate ...

s and glaciers. High elevations on mountains produce Alpine climate, colder climates than at sea level at similar latitude. These colder climates strongly affect the Montane ecosystems, 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, along with recreation, such as mountain climbing and skiing. The highest mountain on Earth is Mount Everest in the Himalayas of Asia, whose summit is above mean sea level. The List of tallest mountains in the Solar System, highest known mountain on any planet in the Solar System is Olympus Mons on Mars at .


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 (Oklahoma), Mount Scott outside Lawton, Oklahoma, USA, is only from its base to its highest point. 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 U.S. 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 United States Geological Survey (USGS) concludes that these terms do not have technical definitions in the US. The UN Environmental Programme'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.


There are three main types of mountains: volcano, volcanic, fold mountain, fold, and fault-block mountain, block. All three types are formed from plate tectonics: when portions of the Earth's crust move, crumple, and dive. Compressional forces, isostasy, isostatic Orogeny, uplift and intrusion of igneous rock, 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 are formed when subduction, a plate is pushed below another plate, or at a mid-ocean ridge or hotspot (geology), hotspot. At a depth of around 100 km, 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 or a stratovolcano. Examples of volcanoes include Mount Fuji 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 (geology), mantle rocks beneath, the weight of any crustal material forced upward to form hills,
plateau In geology Geology (from the Ancient Greek γῆ, ''gē'' ("earth") and -λoγία, ''-logia'', ("study of", "discourse")) is an Earth science concerned with the solid Earth, the rock (geology), rocks of which it is composed, and the proces ...

s or mountains must be isostasy, 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 (geology), fold either symmetrically or asymmetrically. The upfolds are anticlines and the downfolds are synclines: in asymmetric folding there may also be recumbent and overturned folds. The Balkan Mountains and the Jura Mountains are examples of fold mountains.

Block mountains

Block mountains are caused by fault (geology), 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 Horst (geology), horsts. The intervening dropped blocks are termed graben: these can be small or form extensive rift valley systems. This form of landscape can be seen in East Africa, the Vosges Mountains, Vosges and Rhine graben, 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 (geology), crust is thinned.


During and following uplift, mountains are subjected to the agents of
erosion In earth science Earth science or geoscience includes all fields of natural science Natural science is a branch of science Science (from the Latin word ''scientia'', meaning "knowledge") is a systematic enterprise that Scientific ...

(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. Glacier, Glacial processes produce characteristic landforms, such as pyramidal peaks, knife-edge arêtes, and bowl-shaped cirques that can contain lakes. Plateau mountains, such as the Catskills, are formed from the erosion of an uplifted plateau.


Climate in the mountains becomes colder at high elevations, due to an interaction between radiation 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. Note that the presence of water in the atmosphere complicates the process of convection. Water vapor contains latent heat of vaporization. As air rises and cools, it eventually becomes Dew point, 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 100 metres 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 (meteorology), 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 Holdridge life zones, biotemperature, 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 dormancy, dormant, so the exact temperature is unimportant. The peaks of mountains with permanent snow can have a biotemperature below .


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 Biological dispersal, 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 climate, alpine type, resembling tundra. Just below the tree line, one may find subalpine forests of Pinophyta, 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 trees 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 (Ultraviolet, UV). Above elevation, there is not enough oxygen to support human life. This is known 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, 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 parks or ski resorts. About 80% of mountain people live below the poverty line. Most of the world's
river A river is a natural flowing watercourse, usually freshwater, flowing towards an ocean, sea, lake or another river. In some cases, a river flows into the ground and becomes dry at the end of its course without reaching another body of wate ...

s 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 mountains are often seen as preferable "natural boundaries" between polities.


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 (geology), 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 Twelve Olympians, home of the gods. In Japanese culture, the 3,776.24 m (12,389 ft) volcano of Mount Fuji 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 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 crosses are often erected on the tops of prominent mountains.


Heights of mountains are typically measured above sea level. 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, 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 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 ( 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 is the largest non-shield volcano in terms of both base area () and volume (). Mount Logan 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 is not spherical. Sea level closer to the equator is several miles farther from the centre of the Earth. The summit of Chimborazo (volcano), 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 * Lists of mountains *


External links

* * {{Authority control Mountains, Geography terminology Earth's crust