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{{Short description|Large natural elevation of the Earth's surface}}
{{Other uses}}
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{{Use dmy dates|date=January 2020}}
{{Use Canadian English|date=December 2018}}
[[File:Everest North Face toward Base Camp Tibet Luca Galuzzi 2006.jpg|thumb|upright=1.5|[[Mount Everest]], Earth's highest mountain]]

A '''mountain''' is an elevated portion of the [[Earth's crust]], generally with steep sides that show significant exposed [[bedrock]]. 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 {{convert|300|m|ft|lk=on}} above the surrounding land. A few mountains are [[inselberg|isolated summits]], but most occur in [[mountain range]]s.<ref name="agi-1997">{{Cite book |title=Glossary of Geology |publisher=[[American Geological Institute]] |year=1997 |isbn=0922152349 |editor-last=Jackson |editor-first=Julia A. |edition=4th |location=Alexandria, VA |chapter=Mountain}}</ref>

[[mountain formation|Mountains are formed]] through [[tectonic plate|tectonic forces]], [[erosion]], or [[volcanism]],<ref name="agi-1997" /> which act on time scales of up to tens of millions of years.<ref name="levin-2010-83">{{Cite book |last=Levin |first=Harold L. |title=The Earth Through Time |publisher=[[Wiley (publisher)|Wiley]] |year=2010 |isbn=978-0470387740 |edition=9th |location=Hoboken, NJ |page=83}}</ref> Once mountain building ceases, mountains are slowly leveled through the action of [[weathering]], through [[Slump (geology)|slumping]] and other forms of [[mass wasting]], as well as through erosion by [[river]]s and [[glacier]]s.<ref name=":0">{{Cite book |last=Cooke |first=Ronald Urwick |url=https://books.google.com/books?id=RXub68YhovAC&dq=mountains+are+slowly+leveled+through+weathering&pg=PA212 |title=Geomorphology in Deserts |last2=Warren |first2=Andrew |publisher=[[University of California Press]] |year=1973 |isbn=978-0-520-02280-5}}</ref>

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 {{cvt|8850|m|ft|0}} 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 {{cvt|21171|m|ft|0}}. The tallest mountain including submarine terrain is [[Mauna Kea]] in [[Hawaii]] from its underwater base at 9,330 m (30,610 ft) and some scientists consider it to be the tallest on earth.<ref name=":0" />

==Definition==
[[File:Volcán Chimborazo, "El Taita Chimborazo" (cropped).jpg|thumb|upright=1.2|[[Chimborazo]], Ecuador, whose summit is the point farthest away from the Earth's center<ref name="Krulwich2007">{{Cite web |date=7 April 2007 |title=The 'Highest' Spot on Earth |url=https://www.npr.org/templates/story/story.php?storyId=9428163 |url-status=live |archive-url=https://web.archive.org/web/20130130164111/http://www.npr.org/templates/story/story.php?storyId=9428163 |archive-date=30 January 2013 |access-date=31 July 2012 |publisher=Npr.org}}</ref>]]
[[File:Monte Bianco DSF1243-m.jpg|thumb|upright=1.2|[[Mont Blanc]] in [[Aosta Valley]], Italy, the highest point in the [[European Union]]]]
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.<ref name="Gerrard1990" /> 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."<ref name=Gerrard1990/>

Whether a landform is called a mountain may depend on local usage. John Whittow's ''Dictionary of Physical Geography''<ref name="whittow">{{Cite book |last=Whittow |first=John |title=Dictionary of Physical Geography |publisher=Penguin |year=1984 |isbn=0-14-051094-X |location=London |page=352}}</ref> states "Some authorities regard eminences above {{convert|600|m|ft|0}} 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 {{convert|2000|ft|m|0}} high,<ref>{{Cite book |last=Nuttall |first=John & Anne |title=England |publisher=Cicerone |year=2008 |isbn=978-1-85284-037-2 |edition=3rd |series=The Mountains of England & Wales |volume=2 |location=Milnthorpe, Cumbria}}</ref><ref>{{Cite news |title=Survey turns hill into a mountain |url=http://news.bbc.co.uk/2/hi/uk_news/wales/north_west/7623904.stm |url-status=live |archive-url=https://web.archive.org/web/20131002232825/http://news.bbc.co.uk/2/hi/uk_news/wales/north_west/7623904.stm |archive-date=2 October 2013 |access-date=3 February 2013 |work=BBC News}}</ref><ref>{{Cite web |title=A Mountain is a Mountain – isn't it? |url=http://www.go4awalk.com/uk-mountains-and-hills/a-mountain-is-a-mountain.php |url-status=live |archive-url=https://web.archive.org/web/20130208122551/http://www.go4awalk.com/uk-mountains-and-hills/a-mountain-is-a-mountain.php |archive-date=8 February 2013 |access-date=3 February 2013 |website=www.go4awalk.com}}</ref><ref>{{Cite encyclopedia |title=mountain |encyclopedia=Dictionary.reference.com |url=http://dictionary.reference.com/browse/mountain |access-date=3 February 2013 |archive-url=https://web.archive.org/web/20130205033435/http://dictionary.reference.com/browse/Mountain |archive-date=5 February 2013 |url-status=live}}</ref><ref>{{Cite journal |last=Wilson |first=Peter |year=2001 |title=Listing the Irish hills and mountains |url=http://www.ucd.ie/gsi/pdf/34-1/hills.pdf |journal=Irish Geography |location=Coleraine |publisher=University of Ulster |volume=34 |issue=1 |page=89 |doi=10.1080/00750770109555778 |archive-url=https://web.archive.org/web/20130510145742/http://www.ucd.ie/gsi/pdf/34-1/hills.pdf |archive-date=10 May 2013}}</ref> which accords with the official UK government's definition that a mountain, for the purposes of access, is a summit of {{convert|2000|ft|m|0}} or higher.<ref>{{Cite web |title=What is a "Mountain"? Mynydd Graig Goch and all that... |url=http://metricviews.org.uk/2008/09/what-is-a-mountain-mynydd-graig-goch-and-all-that/ |url-status=dead |archive-url=https://web.archive.org/web/20130330062754/https://metricviews.org.uk/2008/09/what-is-a-mountain-mynydd-graig-goch-and-all-that/ |archive-date=30 March 2013 |access-date=3 February 2013 |website=Metric Views}}</ref> In addition, some definitions also include a [[topographical prominence]] requirement, such as that the mountain rises {{convert|300|m|ft|0}} above the surrounding terrain.<ref name="agi-1997" /> At one time, the [[United States Board on Geographic Names]] defined a mountain as being {{convert|1000|ft|m|0}} or taller,<ref>{{Cite web |title=What is the difference between "mountain", "hill", and "peak"; "lake" and "pond"; or "river" and "creek?" |url=https://www.usgs.gov/faqs/what-difference-between-mountain-hill-and-peak-lake-and-pond-or-river-and-creek |website=US Geological Survey}}</ref> 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]] concludes that these terms do not have technical definitions in the US.<ref>{{Cite web |title=What is the difference between lake and pond; mountain and hill; or river and creek? |url=http://gallery.usgs.gov/audios/127 |url-status=live |archive-url=https://web.archive.org/web/20130509082833/http://gallery.usgs.gov/audios/127 |archive-date=9 May 2013 |access-date=11 February 2013 |publisher=USGS}}</ref>

The [[UN Environmental Programme]]'s definition of "mountainous environment" includes any of the following:<ref name=Blyth2002/>{{rp|74}}
* Class 1: Elevation greater than {{cvt|4500|m|ft|0}}.
* Class 2: Elevation between {{cvt|3500|and|4500|m|ft|0}}.
* Class 3: Elevation between {{cvt|2500|and|3500|m|ft|0}}.
* Class 4: Elevation between {{cvt|1500|and|2500|m|ft|0}}, with a slope greater than 2 degrees.
* Class 5: Elevation between {{cvt|1000|and|1500|m|ft|0}}, with a slope greater than 5 degrees or {{cvt|300|m|ft|0}} elevation range within {{cvt|7|km|mi}}.
* Class 6: Elevation between {{cvt|300|and|1000|m|ft|0}}, with a {{cvt|300|m|ft|0|adj=on}} elevation range within {{cvt|7|km|mi}}.
* Class 7: Isolated inner basins and plateaus less than {{cvt|25|km2|mi2}} 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.<ref name=Blyth2002/>{{rp|14}} As a whole, 24% of the Earth's land mass is mountainous.<ref name="panos">{{Cite web |last=Panos |year=2002 |title=High Stakes |url=http://panos.org.uk/wp-content/files/2011/03/high_stakeshVwvcI.pdf |url-status=live |archive-url=https://web.archive.org/web/20120603173156/http://panos.org.uk/wp-content/files/2011/03/high_stakeshVwvcI.pdf |archive-date=3 June 2012 |access-date=17 February 2009}}</ref>

==Geology==
{{Main|Mountain formation|List of mountain types}}
There are three main types of mountains: [[volcanic]], [[fold mountain|fold]], and [[fault-block mountain|block]].<ref name="literacy">{{Cite book |title=Science matters: earth and beyond; module 4 |publisher=Pearson South Africa |year=2002 |isbn=0-7986-6059-7 |page=75 |chapter=Mountain building |chapter-url=https://books.google.com/books?id=qoZftjymxFsC&pg=PA75}}</ref> 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===
{{Main|Volcano}}
[[File:080103 hakkai fuji.jpg|thumb|[[Mount Fuji|Fuji volcano]]]]
Volcanoes are formed when [[subduction|a plate is pushed below another plate]], or at a [[mid-ocean ridge]] or [[hotspot (geology)|hotspot]].<ref name="Butz">{{Cite book |last=Butz |first=Stephen D. |url=https://archive.org/details/isbn_9780766833913/page/136 |title=Science of Earth Systems |publisher=Thompson |year=2004 |isbn=0-7668-3391-7 |page=[https://archive.org/details/isbn_9780766833913/page/136 136] |chapter=Plate tectonics |chapter-url=https://books.google.com/books?id=JB4ArbvXXDEC&pg=PA136}}</ref> At a depth of around {{cvt|100|km|mi|sp=us|sigfig=1}}, 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]].<ref name=Gerrard1990/>{{rp|194}} 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 mountain]]s, such as [[Navajo Mountain]] in the US.<ref>{{Cite book |last=Fillmore |first=Robert |title=Geological evolution of the Colorado Plateau of eastern Utah and western Colorado, including the San Juan River, Natural Bridges, Canyonlands, Arches, and the Book Cliffs |date=2010 |publisher=University of Utah Press |isbn=978-1607810049 |location=Salt Lake City |page=430}}</ref>

===Fold mountains===
{{Main|Fold mountains}}
[[File:Lewis overthrust fault nh10f.jpg|thumb|Illustration of mountains that developed on a [[fold (geology)|fold]] that has been [[Thrust fault|thrust]]]]
Fold mountains occur when two plates collide: shortening occurs along thrust faults and the crust is overthickened.<ref name="Hatcher">{{Cite book |last=Searle |first=Michael P. |title=4-D framework of continental crust |publisher=Geological Society of America |year=2007 |isbn=978-0-8137-1200-0 |editor-last=Hatcher |editor-first=Robert D., Jr. |editor-link=Robert D. Hatcher |pages=41 ff |chapter=Diagnostic features and processes in the construction and evolution of Oman-, Zagros-, Himalayan-, Karakoram-, and Tibetan type orogenic belts |editor-last2=Carlson |editor-first2=M. P. |editor-last3=McBride |editor-first3=J. H. |editor-last4=Martinez Catalán |editor-first4=J. R. |chapter-url=https://books.google.com/books?id=jD-zXhTfJuMC&pg=PA41}}</ref> 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]]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.<ref>{{Cite book |last=Press |first=Frank |url=https://archive.org/details/earth0004pres/page/413 |title=Earth |last2=Siever |first2=Raymond |publisher=W.H. Freeman |year=1985 |isbn=978-0-7167-1743-0 |edition=4th |page=[https://archive.org/details/earth0004pres/page/413 413]}}</ref> Rock can [[fold (geology)|fold]] either symmetrically or asymmetrically. The upfolds are [[anticline]]s and the downfolds are [[syncline]]s: in asymmetric folding there may also be recumbent and overturned folds. The [[Balkan Mountains]]<ref>{{Cite journal |last=Hsü |first=Kenneth J. |last2=Nachev |first2=Ivan K. |last3=Vuchev |first3=Vassil T. |date=July 1977 |title=Geologic evolution of Bulgaria in light of plate tectonics |journal=Tectonophysics |volume=40 |issue=3–4 |pages=245–256 |bibcode=1977Tectp..40..245H |doi=10.1016/0040-1951(77)90068-3}}</ref> and the [[Jura Mountains]]<ref>{{Cite journal |last=Becker |first=Arnfried |date=June 2000 |title=The Jura Mountains — an active foreland fold-and-thrust belt? |journal=Tectonophysics |volume=321 |issue=4 |pages=381–406 |bibcode=2000Tectp.321..381B |doi=10.1016/S0040-1951(00)00089-5}}</ref> are examples of fold mountains.

===Block mountains===
{{Main|Block mountains}}
[[File:Vihren Pirin IMG 8898.jpg|thumb|alt=the highest summit of Pirin|[[Pirin|Pirin Mountain]], Bulgaria, part of the fault-block [[Rila]]-[[Rhodope Mountains|Rhodope]] massif]]
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.<ref name="Ryan">{{Cite book |last=Ryan |first=Scott |url=https://archive.org/details/cliffsquickrevie0000ryan |title=CliffsQuickReview Earth Science |publisher=Wiley |year=2006 |isbn=0-471-78937-2 |chapter=Figure 13-1 |chapter-url=https://books.google.com/books?id=PV_BabxTTkcC&pg=PA94 |url-access=registration}}</ref> 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 kind of landscape can be seen in [[East Africa]],<ref>{{Cite journal |last=Chorowicz |first=Jean |date=October 2005 |title=The East African rift system |journal=Journal of African Earth Sciences |volume=43 |issue=1–3 |pages=379–410 |bibcode=2005JAfES..43..379C |doi=10.1016/j.jafrearsci.2005.07.019}}</ref> the [[Vosges]] and [[Rhine graben|Rhine]] valley,<ref>{{Cite journal |last=Ziegler |first=P. A. |last2=Dèzes |first2=P. |date=July 2007 |title=Cenozoic uplift of Variscan Massifs in the Alpine foreland: Timing and controlling mechanisms |journal=Global and Planetary Change |volume=58 |issue=1–4 |pages=237–269 |bibcode=2007GPC....58..237Z |doi=10.1016/j.gloplacha.2006.12.004}}</ref> and the [[Basin and Range Province]] of Western North America.{{sfn|Levin|2010|pp=474-478}} These areas often occur when the regional stress is extensional and the [[crust (geology)|crust]] is thinned.{{sfn|Levin|2010|pp=474-478}}

===Erosion===
{{Main|Erosion}}
[[File:Slide Mountain Catskills.jpg|thumb|The [[Catskills]] in [[Upstate New York]] represent an eroded [[plateau]].]]
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.<ref name=Fraknoi2004/>{{rp|160}} [[Glacier|Glacial processes]] produce characteristic landforms, such as [[pyramidal peak]]s, knife-edge [[arête]]s, and bowl-shaped [[cirque]]s that can contain lakes.<ref name="thornbury-1969">{{Cite book |last=Thornbury |first=William D. |title=Principles of geomorphology |publisher=Wiley |year=1969 |isbn=0471861979 |edition=2nd |location=New York |pages=358–376}}</ref> [[Plateau]] mountains, such as the [[Catskills]], are formed from the erosion of an uplifted plateau.<ref>{{Cite journal |last=Ver Straeten |first=Charles A. |date=July 2013 |title=Beneath it all: bedrock geology of the Catskill Mountains and implications of its weathering: Bedrock geology and weathering of the Catskills |journal=Annals of the New York Academy of Sciences |volume=1298 |pages=1–29 |doi=10.1111/nyas.12221 |pmid=23895551 |s2cid=19940868}}</ref>

==Climate==
{{Main|Alpine climate}}
[[File:Ural_mountains_3_448122223_93fa978a6d_b.jpg|thumb|The [[Ural Mountains|northern Urals]] at high latitude and elevation have an alpine climate and barren ground.]]
[[File:Villnoess St Magdalena 1.JPG|thumb|The [[Dolomite Mountains]], [[Italy]], in summer. The climate of the Dolomites is characterized by short but warm and mild summers, while winters are long and very cold.]]
Climate in the mountains becomes colder at high [[elevation]]s, 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 {{convert|333|K|C F}}, and the temperature would decay exponentially with height.<ref name="goodywilson">{{Cite book |last=Goody |first=Richard M. |title=Atmospheres |last2=Walker |first2=James C. G. |publisher=Prentice-Hall |year=1972 |chapter=Atmospheric Temperatures |chapter-url=http://lasp.colorado.edu/~bagenal/3720/GoodyWalker/AtmosCh3sm.pdf |archive-url=https://web.archive.org/web/20160729075851/http://lasp.colorado.edu/~bagenal/3720/GoodyWalker/AtmosCh3sm.pdf |archive-date=29 July 2016 |url-status=live}}</ref>

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&nbsp;°C per kilometre (or {{convert|5.4|°F-change|°C-change|abbr=on}} per 1000&nbsp;feet) of altitude.<ref name="goodywilson" />

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 to form clouds and releases heat, which changes the lapse rate from the [[dry adiabatic lapse rate]] to the [[moist adiabatic lapse rate]] (5.5&nbsp;°C per kilometre or {{cvt|3|°F-change|°C-change}} per 1000&nbsp;feet)<ref>{{Cite web |title=Dry Adiabatic Lapse Rate |url=http://meteorologytraining.tpub.com/14312/css/14312_47.htm |url-status=dead |archive-url=https://web.archive.org/web/20160603041448/http://meteorologytraining.tpub.com/14312/css/14312_47.htm |archive-date=3 June 2016 |access-date=2 May 2016 |website=tpub.com}}</ref>
The actual lapse rate can vary by altitude and by location.
Therefore, moving up {{Convert|100|m|ft|abbr=on|sp=us}} on a mountain is roughly equivalent to moving 80&nbsp;kilometres (45&nbsp;miles or 0.75° of [[latitude]]) towards the nearest pole.<ref name="Blyth2002" />{{rp|15}} This relationship is only approximate, however, since local factors such as proximity to oceans (such as the Arctic Ocean) can drastically modify the climate.<ref>{{Cite web |title=Factors affecting climate |url=http://www.ecn.ac.uk/Education/factors_affecting_climate.htm |archive-url=https://web.archive.org/web/20110716163841/http://www.ecn.ac.uk/Education/factors_affecting_climate.htm |archive-date=16 July 2011 |publisher=The United Kingdom Environmental Change Network}}</ref> As the altitude increases, the main form of [[precipitation]] becomes snow and the winds increase.<ref name="Blyth2002" />{{rp|12}}

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]], as described by [[Leslie Holdridge]] in 1947.<ref>{{Cite journal |last=Lugo |first=Ariel E. |last2=Brown |first2=Sandra L. |last3=Dodson |first3=Rusty |last4=Smith |first4=Tom S. |last5=Shugart |first5=Hank H. |year=1999 |title=The Holdridge Life Zones of the conterminous United States in relation to ecosystem mapping |url=http://www.epa.gov/wed/pages/publications/abstracts/archived/lugo.htm |url-status=live |journal=Journal of Biogeography |volume=26 |issue=5 |pages=1025–1038 |bibcode=1999JBiog..26.1025L |doi=10.1046/j.1365-2699.1999.00329.x |s2cid=11733879 |archive-url=https://web.archive.org/web/20130428164559/http://www.epa.gov/wed/pages/publications/abstracts/archived/lugo.htm |archive-date=28 April 2013}}</ref> Biotemperature is the mean temperature; all temperatures below {{convert|0|C|F}} are considered to be 0&nbsp;°C. When the temperature is below 0&nbsp;°C, plants are dormant, so the exact temperature is unimportant. The peaks of mountains with permanent snow can have a biotemperature below {{convert|1.5|C|F}}.

===Climate change===
Mountain environments are particularly sensitive to anthropogenic climate change and are currently undergoing alterations unprecedented in last 10,000 years.<ref>{{Cite journal |last=Knight |first=Jasper |date=24 October 2022 |title=Scientists' warning of the impacts of climate change on mountains |journal=[[PeerJ]] |volume=10 |pages=e14253 |doi=10.7717/peerj.14253 |pmc=9610668 |pmid=36312749 |doi-access=free}}</ref> The effect of global warming on mountain regions (relative to lowlands) is still an active area of study. Observational studies show that highlands are warming faster than nearby lowlands, but when compared globally, the effect disappears.<ref name="Pepin">{{Cite journal |last=Pepin |first=N. C. |last2=Arnone |first2=E. |last3=Gobiet |first3=A. |last4=Haslinger |first4=K. |display-authors=et al |year=2022 |title=Climate Changes and Their Elevational Patterns in the Mountains of the World |url=https://boris.unibe.ch/169026/ |journal=Reviews of Geophysics |volume=60 |issue=1 |bibcode=2022RvGeo..6000730P |doi=10.1029/2020RG000730 |s2cid=247008935 |hdl-access=free |hdl=2318/1842344}}</ref> Precipitation in highland areas is not increasing as quickly as in lowland areas.<ref name="Pepin" /> [[Climate modeling]] give mixed signals about whether a particular highland area will have increased or decreased precipitation.<ref>{{Cite web |last=Derouin |first=Sarah |date=7 November 2023 |title=Carbon Dioxide's Effect on Mountain Climate Systems |url=https://eos.org/research-spotlights/carbon-dioxides-effect-on-mountain-climate-systems |website=Eos}}</ref>

Climate change has started to affect the physical and ecological systems of mountains. In recent decades mountain ice caps and glaciers have experienced accelerating ice loss.<ref>{{Cite book |last=Pelto |first=Mauri |title=Recent Climate Change Impacts on Mountain Glaciers |publisher=Wiley |year=2016 |isbn=9781119068143}}</ref> 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.<ref>{{Cite book |last=Deline |first=Philip |title=Snow and Ice-Related Hazards, Risks, and Disasters |last2=Gruber |first2=Stephan |last3=Amann |first3=Florian |last4=Bodin |first4=Xavier |publisher=Elsevier |year=2021 |isbn=9780128171295 |editor-last=Haeberli |editor-first=Wilfried |edition=2nd |series=Hazards and Disasters |pages=501–540 |chapter=Ice loss from glaciers and permafrost and related slope instability in high-mountain regions |doi=10.1016/B978-0-12-817129-5.00015-9 |display-authors=et al |editor-last2=Whiteman |editor-first2=Colin |s2cid=234301790}}</ref> Patterns of river discharge will also be significantly affected by climate change, which in turn will have 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,<ref>{{Cite journal |last=Viviroli |first=D. |last2=Kummu |first2=M. |last3=Meybeck |first3=M. |last4=Kallio |first4=M. |last5=Wada |first5=Y. |year=2020 |title=Increasing dependence of lowland populations on mountain water resources |journal=Nature Sustainability |volume=3 |issue=11 |pages=917–928 |bibcode=2020NatSu...3..917V |doi=10.1038/s41893-020-0559-9 |s2cid=220375949}}</ref> in particular during the dry season and in semiarid areas such as in central Asia.

Alpine ecosystems can 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.<ref>{{Cite journal |last=Chersich |first=S |last2=Rejšek |first2=K |last3=Vranová |first3=V. |last4=Bordoni |first4=M. |last5=Meisina |first5=C. |year=2015 |title=Climate change impacts on the Alpine ecosystem: an overview with focus on the soil |journal=J. For. Sci. |volume=61 |issue=11 |pages=496–514 |doi=10.17221/47/2015-JFS |doi-access=free}}</ref>

==Ecology==
{{Main|Montane ecology}}
[[File:GlarusAlps.jpg|thumb|An alpine [[Bog|mire]] in the [[Swiss Alps]]]]
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]].<ref>{{Cite journal |last=Daubenmire |first=R. F. |date=June 1943 |title=Vegetational Zonation in the Rocky Mountains |journal=Botanical Review |volume=9 |issue=6 |pages=325–393 |bibcode=1943BotRv...9..325D |doi=10.1007/BF02872481 |s2cid=10413001}}</ref>
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.<ref name=Blyth2002/><ref name="Merriam">{{Cite web |title=Biotic Communities of the Colorado Plateau: C. Hart Merriam and the Life Zones Concept |url=http://cpluhna.nau.edu/Biota/merriam.htm |url-status=dead |archive-url=https://web.archive.org/web/20130114113402/http://www.cpluhna.nau.edu/Biota/merriam.htm |archive-date=14 January 2013 |access-date=30 January 2010}}</ref>

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 island]]s.<ref>{{Cite book |last=Tweit |first=Susan J. |url=https://archive.org/details/greatsouthwestna0000twei/page/209 |title=The Great Southwest Nature Factbook |publisher=[[Alaska Northwest Books]] |year=1992 |isbn=0-88240-434-2 |pages=[https://archive.org/details/greatsouthwestna0000twei/page/209 209–210]}}</ref>

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]].<ref name="Merriam" /> Just below the [[tree line]], one may find [[subalpine]] forests of [[Pinophyta|needleleaf]] trees, which can withstand cold, dry conditions.<ref>{{Cite encyclopedia |year=2002 |title=Tree |encyclopedia=Microsoft Encarta Reference Library 2003 |publisher=Microsoft Corporation |id=60210-442-1635445-74407 |orig-date=1993}}</ref> Below that, [[montane forest]]s grow. In the temperate portions of the earth, those forests tend to be needleleaf trees, while in the tropics, they can be [[broadleaf tree]]s growing in a [[rainforest]].

==Mountains and humans==
{{see also|List of highest cities in the world}}
The highest known permanently tolerable altitude is at {{convert|5950|m|ft}}.<ref name="highestHabitation">{{Cite journal |last=West |first=J. B. |year=2002 |title=Highest permanent human habitation |journal=High Altitude Medical Biology |volume=3 |issue=4 |pages=401–407 |doi=10.1089/15270290260512882 |pmid=12631426}}</ref> 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]]).<ref name="Blyth2002" /> Above {{convert|8000|m|ft}} elevation, there is not enough oxygen to support human life. This is sometimes referred to as the "[[death zone]]".<ref name="PBS">{{Cite web |date=24 February 1998 |title=Everest: The Death Zone |url=https://www.pbs.org/wgbh/nova/transcripts/2506everest.html |url-status=live |archive-url=https://web.archive.org/web/20170618221529/http://www.pbs.org/wgbh/nova/transcripts/2506everest.html |archive-date=18 June 2017 |website=Nova |publisher=PBS}}</ref> The summits of Mount Everest and [[K2]] are in the death zone.
[[File:Mountain regions identified by UNEP.png|thumb|Distribution of mountains by location and elevation]]

===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 {{convert|2500|m|ft}},<ref name="Blyth2002" />{{rp|14}} only 140 million people live above that altitude<ref>{{Cite journal |last=Moore |first=Lorna G. |year=2001 |title=Human Genetic Adaptation to High Altitude |journal=High Alt Med Biol |volume=2 |issue=2 |pages=257–279 |doi=10.1089/152702901750265341 |pmid=11443005}}</ref> and only 20-30 million people above {{convert|3000|m|ft}} elevation.<ref>{{Cite journal |last=Cook |first=James D. |last2=Boy |first2=Erick |last3=Flowers |first3=Carol |last4=del Carmen Daroca |first4=Maria |year=2005 |title=The influence of high-altitude living on body iron |url=http://bloodjournal.hematologylibrary.org/content/106/4/1441.long |journal=Blood |volume=106 |issue=4 |pages=1441–1446 |doi=10.1182/blood-2004-12-4782 |pmid=15870179 |doi-access=free}}</ref> About half of mountain dwellers live in the [[Andes]], Central Asia, and Africa.<ref name="panos" />
[[File:La Paz Skyline.jpg|thumb|The city of [[La Paz]] reaches up to {{convert|4000|m|ft}} in elevation.]]
With limited access to infrastructure, only a handful of human communities exist above {{convert|4000|m|ft}} of elevation. Many are small and have heavily specialized economies, often relying on industries such as agriculture, mining, and tourism.<ref>{{Cite encyclopedia |title=Alps – The economy |encyclopedia=Encyclopædia Britannica |url=https://www.britannica.com/place/Alps/The-economy |access-date=2022-07-13}}</ref> An example of such a specialized town is [[La Rinconada, Peru]], a gold-mining town and the highest elevation human habitation at {{convert|5100|m|ft}}.<ref>{{Cite magazine |last=Finnegan |first=William |date=20 April 2015 |title=Tears of the Sun |url=http://www.newyorker.com/magazine/2015/04/20/tears-of-the-sun |magazine=The New Yorker}}</ref> A counterexample is [[El Alto]], Bolivia, at {{convert|4150|m|ft}}, which has a highly diverse service and manufacturing economy and a population of nearly 1 million.<ref>{{Cite web |title=El Alto, Bolivia: A New World Out of Differences |url=http://upsidedownworld.org/elalto.htm |url-status=dead |archive-url=https://web.archive.org/web/20150516032048/http://upsidedownworld.org/elalto.htm |archive-date=16 May 2015}}</ref>

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 mountain-based societies. More recently, tourism has become more important to the economies of mountain communities, with developments focused around attractions such as [[national park]]s and [[ski resorts]].<ref name="Blyth2002" />{{rp|17}} Approximately 80% of [[mountain people]] live below the poverty line.<ref name="panos" />

Most of the world's rivers are fed from mountain sources, with snow acting as a storage mechanism for downstream users.<ref name="Blyth2002" />{{rp|22}} More than half of humanity depends on mountains for water.<ref>{{Cite web |title=International Year of Freshwater 2003 |url=http://www.wateryear2003.org/en/ev.php-URL_ID=3903&URL_DO=DO_TOPIC&URL_SECTION=201.html |url-status=dead |archive-url=https://web.archive.org/web/20061007104411/http://www.wateryear2003.org/en/ev.php-URL_ID%3D3903%26URL_DO%3DDO_TOPIC%26URL_SECTION%3D201.html |archive-date=7 October 2006 |access-date=7 December 2006}}</ref><ref>{{Cite web |title=The Mountain Institute |url=http://www.mountain.org/mountains/whymtns.cfm?slidepage=water |archive-url=https://web.archive.org/web/20060709060421/http://www.mountain.org/mountains/whymtns.cfm?slidepage=water |archive-date=9 July 2006 |access-date=7 December 2006}}</ref>

In [[geopolitics]], mountains are often seen as [[natural boundaries]] between polities.<ref>{{Cite journal |last=Kolossov |first=V. |year=2005 |title=Border studies: changing perspectives and theoretical approaches |journal=Geopolitics |volume=10 |issue=4 |pages=606–632 |doi=10.1080/14650040500318415 |s2cid=143213848}}</ref><ref>{{Cite journal |last=Van Houtum |first=H. |year=2005 |title=The geopolitics of borders and boundaries |journal=Geopolitics |volume=10 |issue=4 |pages=672–679 |doi=10.1080/14650040500318522}}</ref>

===Mountaineering===
[[File:Ortler_Ascent_-_South_Tyrol.jpg|thumb|upright|Mountaineers climbing in [[South Tyrol]]]]
{{Excerpt|Mountaineering|paragraphs=1–3}}

===Mountains as sacred places===
{{Main|Sacred mountains}}
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.<ref>{{Cite web |title=Mt. Olympus |url=https://sacredsites.com/europe/greece/mt_olympus.html |website=Sacred Sites: World Pilgrimage Guide}}</ref> In Japanese culture, the {{cvt|3,776.24|m|ft}} volcano of [[Mount Fuji]] is also held to be sacred with tens of thousands of Japanese ascending it each year.<ref>{{Cite web |date=6 February 2019 |title=How Mount Fuji became Japan's most sacred symbol |url=https://www.nationalgeographic.com/travel/destinations/asia/japan/climbing-mount-fuji/ |url-status=dead |archive-url=https://web.archive.org/web/20190209081345/https://www.nationalgeographic.com/travel/destinations/asia/japan/climbing-mount-fuji/ |archive-date=9 February 2019 |website=National Geographic}}</ref> [[Mount Kailash]], in the [[Tibet Autonomous Region]] of China, is considered to be sacred in four religions: Hinduism, [[Bon]], Buddhism, and [[Jainism]]. In Ireland, [[pilgrimage]]s are made up the {{convert|952|m|ft}} [[Mount Brandon]] by [[Irish Catholic]]s.<ref>{{Cite web |date=6 June 2016 |title=Mount Brandon |url=https://pilgrimagemedievalireland.com/tag/mount-brandon/ |website=Pilgrimage in Medieval Ireland}}</ref> The [[Himalaya]]n peak of [[Nanda Devi]] is associated with the Hindu goddesses Nanda and Sunanda;<ref>{{Cite web |date=11 August 2015 |title=Nanda Devi |url=https://thecompletepilgrim.com/nanda-devi/ |website=Complete Pilgrim}}</ref> 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]]es are often erected on the tops of prominent mountains.<ref name="Eppacher">{{Cite book |last=Eppacher |first=Wilhelm |title=Berg- und Gipfelkreuze in Tirol |publisher=Universitätsverlag Wagner |year=1957 |editor-last=Klebelsberg |editor-first=Raimund |series=Schlern-Schriften |volume=178 |location=Innsbruck |pages=5–9 |language=de}}</ref>

==Superlatives==
{{Main|List of highest mountains}}
[[File:Comparison of Earth farthest points.svg|thumb|upright|Everest is highest from sea level (green), {{nowrap|Mauna Kea is highest}} from its base (orange), {{nowrap|Cayambe is farthest}} from Earth's axis (pink) and {{nowrap|Chimborazo is farthest}} from Earth's centre (blue)]]
Heights of mountains are typically measured [[above sea level]]. Using this metric, [[Mount Everest]] is the highest mountain on Earth, at {{convert|8848|m|ft}}.<ref>{{Cite news |date=8 April 2010 |title=Nepal and China agree on Mount Everest's height |url=http://news.bbc.co.uk/1/hi/world/south_asia/8608913.stm |url-status=live |archive-url=https://web.archive.org/web/20120303133522/http://news.bbc.co.uk/1/hi/world/south_asia/8608913.stm |archive-date=3 March 2012 |access-date=22 August 2010 |work=BBC News}}</ref> There are at least 100 mountains with heights of over {{convert|7200|m|ft|0}} 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]],<ref name="helman">{{Cite book |last=Helman |first=Adam |title=The Finest Peaks: Prominence and Other Mountain Measures |publisher=[[Trafford]] |year=2005 |isbn=1-4122-3664-9 |page=9 |quote=the base to peak rise of Denali is the largest of any mountain that lies entirely above sea level, some 18,000 feet.}}</ref> [[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]] ({{cvt|4207|m|ft|0}} above sea level) is the world's tallest mountain and volcano, rising about {{cvt|10203|m|ft|0}} from the [[Pacific Ocean]] floor.<ref>{{Cite web |title=Mountains: Highest Points on Earth |url=http://science.nationalgeographic.com/science/earth/surface-of-the-earth/mountains-article/ |url-status=dead |archive-url=https://web.archive.org/web/20100703123427/http://science.nationalgeographic.com/science/earth/surface-of-the-earth/mountains-article |archive-date=3 July 2010 |access-date=19 September 2010 |publisher=National Geographic Society}}</ref>

The highest mountains are not generally the most voluminous. [[Mauna Loa]] ({{cvt|4169|m|ft|0|disp=or}}) is the largest mountain on Earth in terms of base area (about {{cvt|2000|sqmi|km2|-2|disp=or}}) and volume (about {{cvt|18000|mi3|km3|-3|disp=or}}).<ref>{{Cite conference |last=Kaye |first=G. D. |year=2002 |title=Using GIS to estimate the total volume of Mauna Loa Volcano, Hawaii |url=http://gsa.confex.com/gsa/2002CD/finalprogram/abstract_34712.htm |conference=Geological Society of America |archive-url=https://web.archive.org/web/20090125194545/http://gsa.confex.com/gsa/2002CD/finalprogram/abstract_34712.htm |archive-date=25 January 2009 |book-title=98th Annual Meeting |url-status=live}}</ref> [[Mount Kilimanjaro]] is the largest non-shield volcano in terms of both base area ({{cvt|245|sqmi|km2|0|disp=or}}) and volume ({{cvt|1150|mi3|km3|0|disp=or}}). [[Mount Logan]] is the largest non-volcanic mountain in base area ({{cvt|120|sqmi|km2|0|disp=or}}).

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]], 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.<ref name="Krulwich2007" /> Both have elevations above sea level more than {{convert|2|km|ft}} less than that of Everest.

==See also==
{{Portal|Mountains|Environment|Ecology}}
* [[List of mountain ranges]]
* [[List of peaks by prominence]]
* [[List of ski areas and resorts]]
* [[Lists of mountains]]
* {{annotated link|Mountain hut}}
* [[Seven Summits]]

==References==
{{Reflist|refs=
<ref name="Blyth2002">{{Cite web |last=Blyth |first=S. |last2=Groombridge |first2=B. |last3=Lysenko |first3=I. |last4=Miles |first4=L. |last5=Newton |first5=A. |year=2002 |title=Mountain Watch |url=http://www.unep-wcmc.org/mountains/mountain_watch/pdfs/WholeReport.pdf |url-status=dead |archive-url=https://wayback.archive-it.org/all/20080511044709/http://www.unep-wcmc.org/mountains/mountain_watch/pdfs/WholeReport.pdf |archive-date=11 May 2008 |access-date=17 February 2009 |publisher=UNEP World Conservation Monitoring Centre |location=Cambridge}}</ref>
<ref name="Fraknoi2004">{{Cite book |last=Fraknoi |first=A. |url=https://books.google.com/books?id=c5keAQAAIAAJ |title=Voyages to the Planets |last2=Morrison |first2=D. |last3=Wolff |first3=S. |publisher=Thomson |year=2004 |isbn=978-0-534-39567-4 |edition=3rd |location=Belmont}}</ref>
<ref name="Gerrard1990">{{Cite book |last=Gerrard |first=A. J. |url=https://archive.org/details/mountainenvironm0000gerr |title=Mountain Environments: An Examination of the Physical Geography of Mountains |publisher=MIT Press |year=1990 |isbn=978-0-262-07128-4 |location=Cambridge, MA |url-access=registration}}</ref>
}}

{{sister bar|auto=1|s=1911 Encyclopædia Britannica/Mountain}}
{{Earth's landforms}}

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[[Category:Mountains| ]]
[[Category:Geography terminology]]
[[Category:Earth's crust]]