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Mountain — Grokipedia Fact-checked by Grok 3 months ago Mountain Ara Eve Leo Sal 1x A mountain is a prominent landform rising steeply above the surrounding terrain, typically with a relatively small summit area and formed through geological processes that elevate the Earth's crust, such as tectonic plate collisions causing folding and faulting, or accumulation of volcanic material. [1] [2] Mountains are primarily classified by formation mechanisms into fold mountains, resulting from compressional tectonic forces that buckle rock layers; fault-block mountains, created by crustal fracturing and differential uplift along faults; volcanic mountains, built from successive eruptions of lava and ash; and dome mountains, arising from igneous intrusions that arch overlying strata. [3] [4] The tallest mountain above sea level is Mount Everest, with a height of 8,848 meters, exemplifying the dramatic scale achievable through ongoing orogenic activity at convergent plate boundaries. [5] These features shape global topography, influencing weather patterns by blocking atmospheric flows, fostering unique ecosystems at varying altitudes, and historically serving as natural fortifications and mineral resources for human societies, though their formation continues dynamically due to plate tectonics. [2] [6] Definition and Classification Defining Mountains A mountain is a landform characterized by a prominent rise above its surrounding terrain , typically featuring steep slopes, a relatively narrow summit area, and significant local relief, often resulting from tectonic uplift or volcanic activity. [6] Unlike flatter or more gradual elevations, mountains generally exhibit exposed bedrock and rugged morphology due to their formation processes. [1] There exists no universally agreed-upon quantitative criterion for distinguishing mountains from other elevated features, with classifications varying by region, authority, and purpose; the U.S. Geological Survey notes that terms like " mountain " lack official definitions in geographic nomenclature , relying instead on subjective assessments of relief , slope , and form. [7] [8] Common heuristics include a minimum local relief — the vertical difference between the summit and adjacent low points—of at least 300 meters (approximately 1,000 feet), as referenced in historical guidelines from bodies like the U.S. Board on Geographic Names and the British Ordnance Survey . [9] [8] Topographic prominence offers a more precise metric for evaluating a mountain's topographic independence, calculated as the summit's elevation minus the height of the highest saddle ( col ) connecting it to a taller peak, effectively measuring the minimum descent required to reach higher terrain . [10] For instance, peaks with prominence exceeding 600 meters are often classified as major mountains in mountaineering contexts, though thresholds like 1,500 meters (ultr_prominent peaks) highlight globally significant features independent of absolute elevation . [11] This approach prioritizes causal topographic structure over arbitrary height cutoffs, revealing that low- elevation but highly prominent rises, such as isolated volcanic cones, qualify as mountains despite modest absolute heights. [10] In practice, global inventories, such as those by the United Nations Environment Programme , delineate mountain regions using elevation thresholds (e.g., over 300 meters in low-relief areas or prominence-based isolations), encompassing about 25% of Earth's land surface and emphasizing ecological and hydrological roles over strict morphological purity. [12] These definitions evolve with geospatial data, underscoring that mountains are not merely tall hills but dynamically formed structures integral to planetary geomorphology . [1] Distinctions from Hills and Plateaus Mountains are distinguished from hills primarily by differences in scale, elevation , and topographic prominence , though no universally accepted geological criterion exists to delineate the two. The United States Geological Survey states that generic terms like "mountain" and "hill" lack official definitions, with distinctions being subjective and based on local relief , slope steepness, and cultural perception rather than absolute height thresholds. [7] Commonly, mountains exhibit greater local relief —often exceeding 300 meters (1,000 feet) above surrounding terrain—and feature steeper slopes with distinct peaks or ridges, whereas hills typically rise less than 200-300 meters with gentler, more rounded contours and subdued summits. [9] [13] Historical guidelines, such as the British Ordnance Survey's former use of 305 meters (1,000 feet) as a cutoff for elevation prominence, illustrate regional variations, but these are not applied globally due to diverse landscapes; for instance, the Black Hills in South Dakota include peaks over 2,200 meters classified as mountains despite lower prominence in some contexts. [8] Plateaus differ from mountains in their predominantly flat, elevated surfaces with minimal relief, contrasting the rugged, peaked morphology of mountainous terrain. Geologically, plateaus form through broad uplift or volcanic accumulation followed by limited erosion, resulting in extensive horizontal strata often bounded by steep escarpments, as seen in the Colorado Plateau's 1,800-meter average elevation with vast tablelands rather than discrete summits. [14] Mountains, by comparison, arise from intense tectonic compression or volcanism producing irregular elevations with valleys and spurs, lacking the plateau's characteristic planation. While some plateaus host superimposed mountains (e.g., the Ethiopian Highlands), the primary distinction lies in overall form: plateaus emphasize lateral extent and flatness over vertical prominence, with slopes concentrated at margins rather than distributed as in mountain systems. [15] This morphological contrast underscores causal differences in formation, where plateaus reflect crustal stability post-uplift and mountains ongoing dynamism. Geological Formation Tectonic Processes Mountains primarily form through orogenic processes at convergent plate boundaries, where tectonic plates collide, leading to crustal deformation, folding, faulting, and uplift. [3] These processes, driven by the movement of lithospheric plates at rates of 1-10 cm per year, result in the compression and thickening of the Earth's crust , often exceeding 50 km in depth beneath major ranges. [2] Isostatic rebound contributes to elevation as buoyant crustal roots rise following material addition. [16] In subduction zones, where an oceanic plate descends beneath a continental plate, compressional forces generate fold-thrust belts and volcanic arcs parallel to the margin. The Andes exemplify this, formed by the Nazca Plate subducting under the South American Plate at approximately 6-10 cm per year, initiating major uplift around 25-30 million years ago with peaks reaching over 6,000 meters. [17] Magmatism and metamorphism accompany this, as slab dehydration triggers partial melting in the mantle wedge. [18] Continental-continental collisions produce the most dramatic non-volcanic ranges, as neither plate subducts easily due to buoyancy , instead causing intense shortening and crustal doubling. The Himalayas arose from the Indian Plate colliding with the Eurasian Plate starting about 50 million years ago, at a convergence rate of 4-5 cm per year, thickening the crust to 70 km and elevating Mount Everest to 8,849 meters. [19] Thrust faults, like the Main Central Thrust , accommodate hundreds of kilometers of shortening through ductile flow and brittle faulting. [20] Transform boundaries and intraplate stresses can also contribute to localized uplift, such as in the Sierra Nevada via earlier subduction followed by extension, but these are secondary to convergent mechanisms for global mountain belts. [21] Ongoing tectonics ensure continued growth, with rates of 1-10 mm per year in active orogens like the Himalayas . [22] Primary Mountain Types Fold mountains form through compressional forces at convergent tectonic plate boundaries, where colliding plates cause sedimentary rock layers to buckle, shorten, and fold into anticlines and synclines. This process, driven by plate subduction or continental collision, builds extensive ranges over millions of years; for instance, the ongoing convergence of the Indian and Eurasian plates at 4-5 cm per year has elevated the Himalayas to average heights exceeding 6,000 meters since their initiation around 50 million years ago. [23] Examples include the Alps, formed by the African plate's northward push against Eurasia starting in the Eocene epoch, and the Appalachian Mountains, remnants of an ancient Paleozoic collision. [24] Fault-block mountains arise from extensional tectonics , where tensional stresses fracture the crust along normal faults, uplifting intact blocks while adjacent areas subside into basins, often in rift zones or behind subduction areas. The Sierra Nevada range in California exemplifies this, with its eastern escarpment defined by the Sierra Nevada fault, which has displaced blocks by up to 10 km vertically over the past 10 million years. [25] [26] Similarly, the Grand Teton Mountains in Wyoming feature sharp peaks from recent faulting, with uplift rates of about 1-2 mm per year along the Teton fault. [27] Volcanic mountains build from repeated eruptions of magma that accumulate as lava flows, pyroclastic deposits, and domes at hotspots, divergent boundaries, or subduction zones, creating stratovolcanoes or shield volcanoes . Mauna Loa in Hawaii , a shield volcano , has grown to 4,169 meters above sea level through fluid basaltic eruptions since at least 700,000 years ago, with its total height from the ocean floor exceeding 9,000 meters. [28] Mount Fuji in Japan , a stratovolcano , formed over 100,000 years from andesitic eruptions linked to Pacific plate subduction . [29] Dome mountains deve