Mountain formation occurs due to a variety of geological processes associated with large-scale movements ofEarth's crust (tectonic plates).^[1]Folding,faulting,volcanic activity,igneous intrusion andmetamorphism can all be parts of theorogenic process ofmountain building.^[2] The formation of mountains is not necessarily related to thegeological structures found on it.^[3]

From the late 18th century until its replacement byplate tectonics in the 1960s,geosyncline theory was used to explain much mountain-building.^[4] The understanding of specific landscape features in terms of the underlyingtectonic processes is calledtectonic geomorphology, and the study of geologically young or ongoing processes is calledneotectonics.^{[5][clarification needed]}

There are five main types of mountains:volcanic,fold,plateau,fault-block, anddome. A more detailed classification useful on a local scale predatesplate tectonics and adds to these categories.^[6]

Movements of tectonic plates createvolcanoes along the plate boundaries, which erupt and form mountains. Avolcanic arc system is a series of volcanoes that form near asubduction zone where the crust of a sinkingoceanic plate melts and drags water down with the subducting crust.^[8]

Most volcanoes occur in a band encircling the Pacific Ocean (thePacific Ring of Fire), and in another that extends from the Mediterranean across Asia to join the Pacific band in the Indonesian Archipelago. The most important types of volcanic mountain arecomposite cones orstratovolcanoes andshield volcanoes.^[9][10]

A shield volcano has a gently sloping cone because of the low viscosity of the emitted material, primarilybasalt.Mauna Loa is the classic example, with a slope of 4°-6°. (The relation between slope and viscosity falls under the topic ofangle of repose.^[11]) A composite volcano or stratovolcano has a more steeply rising cone (33°-40°),^[12] because of the higher viscosity of the emitted material, anderuptions are more violent and less frequent than for shield volcanoes. Examples includeVesuvius,Kilimanjaro,Mount Fuji,Mount Shasta,Mount Hood andMount Rainier.^[13]

Whenplates collide or undergosubduction (that is, ride one over another), the plates tend to buckle andfold, forming mountains. While volcanic arcs form at oceanic-continental plate boundaries, folding occurs at continental-continental plate boundaries. Most of the major continental mountain ranges are associated with thrusting and folding ororogenesis. Examples are theBalkan Mountains, theJura and theZagros mountains.^[14]

When afault block is raised or tilted, a block mountain can result.^[16] Higher blocks are calledhorsts, and troughs are calledgrabens. A spreading apart of the surface causes tensional forces. When the tensional forces are strong enough to cause a plate to split apart, it does so such that a center block drops down relative to its flanking blocks.

An example is theSierra Nevada range, wheredelamination created a block 650 km long and 80 km wide that consists of many individual portions tipped gently west, with east facing slips rising abruptly to produce the highest mountain front in the continental United States.^[17][18]

Another example is theRila–Rhodopemassif inBulgaria, including the well defined horsts ofBelasitsa (linear horst), Rila mountain (vaulted domed shaped horst) andPirin mountain—a horst forming a massiveanticline situated between the complex graben valleys of theStruma andMesta rivers.^[19][20][21]

Unlike orogenic mountains there is no widely acceptedgeophysical model that explains elevated passivecontinental margins such as theScandinavian Mountains, easternGreenland, theBrazilian Highlands, or Australia'sGreat Dividing Range.^[22][23]Different elevated passive continental margins most likely share the same mechanism of uplift. This mechanism is possibly related to far-field stresses in Earth'slithosphere. According to this view elevated passive margins can be likened to giantanticlinal lithospheric folds, where folding is caused by horizontal compression acting on a thin to thick crust transition zone (as are all passive margins).^[24][25]

Hotspots are supplied by amagma source in theEarth's mantle called amantle plume. Although originally attributed to a melting of subducted oceanic crust, recent evidence belies this connection.^[26] The mechanism for plume formation remains a research topic.

Several movements of Earth's crust that lead to mountains are associated withfaults. These movements actually are amenable to analysis that can predict, for example, the height of a raised block and the width of an intervening rift between blocks using therheology of the layers and the forces ofisostasy. Early bent plate models predicting fractures and fault movements have evolved into today's kinematic and flexural models.^[27][28]

• 3D fold evolution
• Continental collision – Phenomenon in which mountains can be produced on the boundaries of converging tectonic plates
• Cycle of erosion – Model of geographic landscape evolution
• Inselberg – Isolated, steep rock hill on relatively flat terrain
• Seamount – Mountain rising from the ocean seafloor that does not reach the water's surface

• NASA Goddard Planetary Geodynamics Laboratory
• NASA Goddard Planetary Geodynamics Laboratory: Volcanology Research
• Rotating globe showing areas of earthquake activity

• Mountains
• Orogeny
• Geological processes
• Plate tectonics

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• Wikipedia articles needing clarification from January 2017