Mountain

A mountain is, essentially, a monumental piece of the Earth's crust that decided to stand up and make a statement. It's an elevation, often quite dramatic, with sides so steep they seem to glare at you, and usually, you can see the raw, unvarnished bedrock peeking through. While definitions can be as fuzzy as a mountain fog, a mountain typically distinguishes itself from a mere plateau by having a defined, often limited, summit. It’s generally taller than a hill, usually by a respectable margin of at least 600 metres (about 2,000 ft) above the surrounding terrain. You’ll find them standing alone, like defiant sentinels (Inselberg), or more commonly, clustered together in grand, imposing mountain ranges.[1]

These titans of the landscape don't just appear. They are sculpted by the colossal forces of tectonic plates grinding against each other, the relentless artistry of erosion, or the fiery temperament of volcanism.[1] This geological drama can unfold over eons, stretching into tens of millions of years.[2] And even after the initial upheaval ceases, the mountains don't get to rest. They are slowly, inexorably, worn down by the relentless elements: weathering, the slow slide of slumping and other forms of mass wasting, and the persistent carving by rivers and glaciers.[3]

The sheer altitude of mountains dictates their climate. Up there, it’s significantly colder than at sea level at the same latitude. This stark difference in temperature profoundly shapes the life that can survive. You'll find distinct ecosystems at different elevations, each with its own unique cast of plants and animals. Because the terrain is so unforgiving and the climate so harsh, mountains are rarely the go-to for extensive agriculture. Instead, they tend to be exploited for their resources, like mining and logging, or visited for recreation, offering thrilling challenges like mountain climbing and the exhilaration of skiing.

The undisputed monarch of Earth's mountains, in terms of sheer height above sea level, is Mount Everest in the Himalayas of Asia, its summit a staggering 8,850 metres (29,035 ft) above the waves. But if we cast our gaze to other planets, Mars boasts Olympus Mons, a colossal volcano that dwarfs anything on Earth, reaching a mind-boggling 21,171 metres (69,459 ft). And then there's [Mauna Kea](/Mauna Kea) in Hawaii, a behemoth that, when measured from its submerged base on the ocean floor, stretches an astonishing 9,330 m (30,610 ft). Some scientists argue this underwater giant is, in fact, the tallest mountain on our planet.[3]

Definition

Chimborazo, Ecuador, proudly holds the title of being the point farthest from the Earth's center. [4] Meanwhile, Mont Blanc, straddling the border between Aosta Valley, Italy, and Haute-Savoie, France, stands as the loftiest peak within the European Union.

The truth is, there's no single, universally agreed-upon definition of what constitutes a mountain. Authorities have wrangled over criteria like elevation, sheer volume, the dramatic relief between peak and base, the steepness of its slopes, how closely it's packed with other peaks, and its overall continuity.[5] The venerable Oxford English Dictionary offers a definition: "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." [5]

Ultimately, what one person calls a mountain, another might just see as a particularly ambitious hill. It often comes down to local parlance. John Whittow, in his Dictionary of Physical Geography, notes that "Some authorities regard eminences above 600 metres (1,969 ft) as mountains, those below being referred to as hills." [6][7]

In the British Isles, the convention often dictates that a summit must reach at least 2,000 feet (610 metres) to earn the title of mountain.[8][9][10][11][12] The official stance of the UK government, for access purposes, aligns with this, defining a mountain as any summit of 2,000 feet (610 metres) or higher.[13] Beyond mere height, some definitions also factor in topographical prominence, requiring a peak to rise a significant 300 metres (984 ft) above its immediate surroundings.[1] The United States Board on Geographic Names used to consider anything 1,000 feet (305 metres) or taller a mountain,[14] but this technical definition was abandoned decades ago. Today, the United States Geological Survey admits that these terms, "mountain" and "hill," lack any precise technical definition within the US.[15]

The UN Environmental Programme has its own, rather detailed, classification for "mountainous environments," which includes: [16]: 74

Class 1: Elevations exceeding 4,500 metres (14,764 ft).
Class 2: Elevations ranging from 3,500 to 4,500 metres (11,483 to 14,764 ft).
Class 3: Elevations between 2,500 and 3,500 metres (8,202 to 11,483 ft).
Class 4: Elevations from 1,500 to 2,500 metres (4,921 to 8,202 ft), coupled with slopes steeper than 2 degrees.
Class 5: Elevations between 1,000 and 1,500 metres (3,281 to 4,921 ft), with slopes exceeding 5 degrees, or a significant elevation range of 300 metres (984 ft) within a 7 km (4.3 mi) radius.
Class 6: Elevations from 300 to 1,000 metres (984 to 3,281 ft), featuring an elevation range of 300 metres (984 ft) within a 7 km (4.3 mi) radius.
Class 7: Isolated inland basins and plateaus, smaller than 25 km² (9.7 sq mi), completely encircled by mountains of Class 1 to 6, but not meeting those criteria themselves.

By these standards, mountains cover a substantial 33% of Eurasia, 19% of South America, 24% of North America, and 14% of Africa.[16]: 14 Globally, a significant 24% of the Earth's landmass can be classified as mountainous.[17]

Geology

See also: Mountain formation and List of mountain types

Mountains generally fall into three primary categories: volcanic, fold, and block.[18] All these formations are ultimately a consequence of plate tectonics – the movement, collision, and subduction of the Earth's crustal plates. Whether through compressional forces, the slow uplift of isostasy, or the intrusion of molten igneous matter, the crust is pushed upward, creating landforms that rise above their surroundings. The resulting elevation determines whether we call it a hill or, if it's sufficiently tall and steep, a mountain. The most prominent mountain ranges often trace the boundaries of these tectonic plates, a testament to their dynamic origins.

Volcanoes

See also: Volcano

Fuji volcano is a prime example of a volcanic mountain. Volcanoes are born from the dramatic processes where one tectonic plate slides beneath another (subduction), or at the seams of the Earth's crust (mid-ocean ridges), or from deep within the mantle at hotspots.[19] Around 100 kilometres (60 mi) deep, the rock above a subducting plate melts, forming magma. This molten rock then ascends, eventually erupting at the surface to build volcanic mountains, whether they are broad shield volcanoes or the more conical stratovolcanoes.[5]: 194 Iconic examples include Japan's Mount Fuji and the Philippines' Mount Pinatubo. It's not always necessary for magma to reach the surface to create a mountain; magma that cools and solidifies beneath the ground can also push the overlying rock upwards, forming dome mountains like Navajo Mountain in the United States.[20]

Fold Mountains

See also: Fold mountains

This illustration depicts mountains formed by folding and thrusting of the Earth's crust. Fold mountains arise when two continental plates collide. This immense pressure causes the crust to shorten and thicken along thrust faults.[21] Because the less dense continental crust essentially "floats" on the denser mantle beneath it, any crustal material pushed upward to form mountains must be counterbalanced by a much larger volume being forced downwards into the mantle – a concept known as isostasy.[22] This results in a significantly thicker crust beneath mountain ranges compared to adjacent lowlands. The rock layers can fold symmetrically or asymmetrically. Upward folds are called anticlines, and downward folds are synclines. In asymmetrical folding, you might also find recumbent and overturned folds. The Balkan Mountains[23] and the Jura Mountains[24] are classic examples of fold mountains.

Block Mountains

See also: Block mountains

Pirin Mountain in Bulgaria, part of the fault-block Rila-Rhodope massif, showcases block mountain topography. Block mountains are the result of faults – fractures in the Earth's crust where rocks have moved past each other. When one side of a fault is uplifted relative to the other, mountains can form.[25] These uplifted blocks are known as horsts, while the adjacent, down-dropped blocks are called grabens. These grabens can range from small depressions to vast rift valley systems, such as those found in East Africa,[26] the Vosges and Rhine valley,[27] and the extensive Basin and Range Province of western North America.[28] These landscapes often form where the Earth's crust is being stretched and thinned by extensional forces.[28]

Erosion

See also: Erosion

The Apennine Mountains in Italy, with the Trebbia river winding through them. Even as mountains are being uplifted, they are simultaneously being sculpted and worn down by the relentless forces of erosion, including water, wind, ice, and gravity. This process ensures that the visible surface of mountains is generally much younger than the ancient rocks that form their core.[29]: 160 Glacial activity, in particular, carves out dramatic and distinctive landforms: sharp, pointed pyramidal peaks, knife-edge ridges known as arêtes, and steep, bowl-shaped depressions called cirques, which often fill with water to form lakes.[30] Plateau mountains, like the Catskills, are formed when uplifted plateaus are dissected by erosion.[31]

Climate

See also: Alpine climate

The northern Urals, situated at high latitude and elevation, exhibit an alpine climate with barren ground. The Dolomite Mountains in Italy during summer. Their climate is characterized by short, mild summers and long, harsh winters.

As you ascend a mountain, the temperature drops. This cooling is a consequence of how solar radiation interacts with the Earth's surface and atmosphere. Sunlight warms the ground, which in turn heats the air above it. In a vacuum, without an atmosphere, the ground would radiate heat directly into space, leading to extreme temperature fluctuations.[32]

However, the atmosphere acts as an insulator, and the process of convection plays a crucial role. Warmer, less dense air rises, carrying heat upward. This process continues until the rising parcel of air reaches an equilibrium with its surroundings – a state where it has the same density. Since air is a poor conductor of heat, this rising and falling happens largely without heat exchange, an adiabatic process. A key characteristic of this process is that as air expands due to lower pressure at higher altitudes, it cools. This rate of cooling with increasing elevation is called the adiabatic lapse rate, typically around 9.8 °C per kilometre (or 5.4 °F per 1000 ft).[32]

The presence of water vapor in the atmosphere adds complexity. Water has a high heat of vaporization. As air rises and cools, it eventually reaches its saturation point, and the water vapor condenses into clouds, releasing heat. This release of heat alters the cooling rate from the dry adiabatic lapse rate to the moist adiabatic lapse rate, which is approximately 5.5 °C per kilometre (or 3 °F per 1000 ft).[33] The actual lapse rate can vary significantly depending on altitude and geographical location.

Essentially, climbing 100 metres (330 ft) up a mountain is roughly equivalent to travelling 80 kilometres (45 miles or 0.75° of latitude) towards the North or South Pole in terms of temperature change.[16]: 15 This is a generalization, of course, and local factors, like proximity to large bodies of water such as the Arctic Ocean, can dramatically influence the climate.[34] As elevation increases, precipitation tends to fall as snow, and wind speeds generally increase.[16]: 12

The relationship between climate and the life found at different elevations was elegantly described by Leslie Holdridge in 1947, using a combination of precipitation levels and biotemperature. Biotemperature is the average temperature, with any temperature below 0 °C (32 °F) counted as 0 °C, as plants remain dormant below freezing. Mountain peaks perpetually covered in snow might have a biotemperature below 1.5 °C (34.7 °F).

Climate Change

Mountain environments are acutely vulnerable to anthropogenic climate change, and they are currently undergoing transformations at a rate unseen in the last 10,000 years.[36] While it's often stated that highlands warm faster than lowlands, global comparisons reveal this isn't universally true.[37] Similarly, precipitation increases in mountainous areas don't always keep pace with those in lowlands.[37] Climate modeling offers mixed predictions, with some suggesting increased precipitation in certain highland areas and others predicting decreases.[38]

The tangible effects of climate change are already evident in the physical and ecological systems of mountains. In recent decades, mountain ice caps and glaciers have been melting at an accelerating rate.[39] This meltwater, along with thawing permafrost and snowpack, destabilizes the underlying ground, leading to an increase in both the frequency and magnitude of landslips.[40] River discharge patterns are also being significantly altered, impacting communities that depend on these alpine water sources. It's estimated that nearly half of the world's mountainous regions provide essential water resources for predominantly urban populations,[41] especially critical during dry seasons in semi-arid regions like Central Asia.

Alpine ecosystems, often occupying narrow climatic niches, are particularly susceptible.[42] Changes in climate not only directly affect these ecosystems but also indirectly impact soil stability and development.

Ecology

See also: Montane ecology

An alpine mire in the Swiss Alps. The colder climate at higher elevations profoundly influences the plants and animals that inhabit mountains. Many species are adapted to a specific, narrow range of climatic conditions, leading to the formation of distinct ecological bands corresponding to elevation. This phenomenon is known as altitudinal zonation.[43] In arid regions, mountains often receive more precipitation and experience lower temperatures, further enhancing this zonation effect.[16][44]

These distinct altitudinal zones can lead to the isolation of plant and animal populations. The conditions above and below a particular zone may be too harsh to allow for movement or biological dispersal, effectively creating ecological "islands" in the sky.[45]

The typical pattern of altitudinal zonation is as follows: at the highest elevations, where trees cannot survive, the vegetation resembles tundra, characteristic of the alpine zone.[44] Just below the tree line, subalpine forests, typically composed of needleleaf trees that can tolerate cold, dry conditions, are found.[46] Lower still are the montane forests. In temperate regions, these are usually coniferous forests, while in the tropics, they can be lush broadleaf rainforests.

Mountains and Humans

See also: List of highest cities in the world

The highest altitude humans can permanently and tolerably inhabit is around 5,950 metres (19,520 ft).[47] Beyond this, the decreasing atmospheric pressure means less oxygen is available for breathing, and there's reduced protection from intense solar UV radiation.[16] Above 8,000 metres (26,000 ft), the oxygen levels are insufficient to sustain human life, a region ominously known as the "death zone".[48] The summits of Mount Everest and K2 lie within this perilous zone.

Distribution of mountains by location and elevation

Mountain societies and economies

Mountains are generally less hospitable to human settlement than lowlands, presenting challenges with harsh weather and limited flat land suitable for agriculture. While 7% of the Earth's land surface is above 2,500 metres (8,200 ft),[16]: 14 only about 140 million people live above this altitude,[49] with roughly 20–30 million residing above 3,000 metres (9,800 ft).[50] Approximately half of these mountain dwellers are concentrated in the Andes, Central Asia, and Africa.[17]

The city of La Paz, Bolivia, reaches elevations up to 4,000 metres (13,000 ft), with the imposing Mount Illimani dominating its skyline.

Due to limited infrastructure, very few human communities exist above 4,000 metres (13,000 ft). Those that do are often small, with highly specialized economies centered on industries like mining, agriculture, and tourism.[51] La Rinconada, Peru, a gold-mining town at 5,100 metres (16,700 ft), is a prime example of such a specialized settlement and holds the distinction of being the highest human habitation on Earth.[52] In contrast, El Alto, Bolivia, situated at 4,150 metres (13,620 ft), boasts a surprisingly diverse economy encompassing services and manufacturing, supporting a population nearing one million.[53]

Traditional mountain societies often depend heavily on agriculture, facing a higher risk of crop failure compared to their lowland counterparts. Mountains are also rich in minerals, making mining a significant economic driver for many mountain communities. In more recent times, tourism has become increasingly vital, with developments often focused on natural attractions like national parks and ski resorts.[16]: 17 Sadly, around 80% of mountain people live below the poverty line.[17]

A vast number of the world's rivers originate in mountains, with snowpack acting as a crucial natural reservoir for downstream water users.[16]: 22 It's estimated that over half of humanity relies on mountains for their water supply.[54][55]

From a geopolitical perspective, mountains have historically served as formidable natural boundaries between nations and regions.[56][57]

Contemporary development studies highlight the critical role of transportation networks in fostering economic growth, improving socio-economic well-being, and reducing poverty.[58] However, the development of road networks hasn't always yielded the intended benefits. In some instances, it has contributed significantly to environmental degradation and, regrettably, led to the erosion of cultural traditions and the marginalization of indigenous populations.[59][60] The impact of air transport development, particularly helicopters and planes, has often been even more disruptive. Furthermore, the use of helicopters for tourism activities has drawn considerable criticism regarding their environmental impact and adherence to sports ethics.[61]

Mountaineering

This section is an excerpt from Mountaineering.

Climbers ascend Mount Rainier in the United States, with Little Tahoma Peak visible in the distance. Mountaineering, also known as mountain climbing or alpinism,[62] encompasses a range of outdoor activities focused on ascending mountains. This includes traditional rock and ice climbing, skiing in mountainous terrain, and navigating via ferratas, all of which have evolved into distinct sports.[63][64][65][66] Some also consider disciplines like indoor climbing, sport climbing, and bouldering as forms of mountaineering,[67][68] though they belong to a broader category of mountain sports.

Unlike many sports, mountaineering lacks a universally applied set of formal rules, regulations, or governing bodies. Instead, mountaineers navigate using a diverse array of techniques and adhere to various philosophical approaches, often guided by grading systems and guidebooks.[68][69] Numerous local alpine clubs provide resources and foster community among mountaineers. The International Climbing and Mountaineering Federation (UIAA), recognized by the International Olympic Committee, serves as the global authority for mountaineering and climbing.[70] The environmental impact of mountaineering can be observed across various aspects of the natural landscape, affecting landforms, soil, vegetation, fauna, and the overall scenery in areas where these activities take place.[71] On a human level, mountaineering influences communities economically, politically, socially, and culturally, often leading to shifts in perspectives influenced by globalization and exposure to foreign cultures and lifestyles.[72]

Mountains as sacred places

See also: Sacred mountains

Mountains frequently hold profound religious significance. In Greece, for instance, Mount Olympus was revered as the abode of the gods.[73] Within Japanese culture, the iconic Mount Fuji, a volcano standing at 3,776.24 metres (12,389.2 ft), is considered sacred, drawing tens of thousands of pilgrims annually.[74] Mount Kailash, located in the Tibet Autonomous Region of China, holds spiritual importance for four major religions: Hinduism, Bon, Buddhism, and Jainism. In Ireland, Catholics undertake pilgrimages up the 952-metre (3,123 ft) Mount Brandon.[75] The Himalayan peak of Nanda Devi is deeply connected to the Hindu goddesses Nanda and Sunanda;[76] climbing has been prohibited there since 1983. Mount Ararat is considered sacred due to its association with the biblical landing site of Noah's Ark. Across Europe, particularly in the Alps, it's common to find summit crosses erected on prominent mountain peaks.[77]

Superlatives

See also: List of highest mountains

The diagram illustrates the different ways mountain heights are measured: Everest is the highest above sea level (green), Mauna Kea is the highest from its base (orange), Cayambe is farthest from Earth's axis (pink), and Chimborazo is farthest from Earth's center (blue). When measuring mountain height, the standard convention is to use elevation above sea level. By this measure, Mount Everest reigns supreme as the highest mountain on Earth, reaching 8,848 metres (29,029 ft).[78] There are at least 100 mountains globally that exceed 7,200 metres (23,622 ft) above sea level, all located in the central and southern regions of Asia. However, the highest mountains above sea level are not necessarily the tallest when measured from their surrounding base. While the definition of a "surrounding base" can be ambiguous, peaks like Denali,[79] Mount Kilimanjaro, and Nanga Parbat are contenders for the title of tallest mountain on land based on this metric. For mountain islands, their bases lie beneath the sea. Considering this, Mauna Kea, with an elevation of 4,207 m (13,802 ft) above sea level, is arguably the world's tallest mountain and volcano, rising an astounding 10,203 m (33,474 ft) from the floor of the Pacific Ocean.[80]

The most voluminous mountains are not necessarily the highest. Mauna Loa (4,169 m or 13,678 ft) claims the title of the largest mountain on Earth in terms of its base area (approximately 5,200 km² or 2,000 sq mi) and its sheer volume (around 75,000 km³ or 18,000 cu mi).[81] Mount Kilimanjaro is the largest non-shield volcano, both in base area (635 km² or 245 sq mi) and volume (4,793 km³ or 1,150 cu mi). Mount Logan holds the record for the largest non-volcanic mountain by base area (311 km² or 120 sq mi).

The peaks farthest from the Earth's center are also not always the highest above sea level, due to the Earth's non-spherical shape. The sea level near the equator is several miles farther from the Earth's center than at the poles. The summit of Chimborazo, Ecuador's highest mountain, is generally considered the farthest point from the Earth's center. However, the southern summit of Peru's tallest mountain, Huascarán, is another strong contender.[4] Both of these peaks have elevations above sea level more than 2 kilometres (6,600 ft) lower than Mount Everest.