Mountain formation
Mountain formation occurs due to a variety of geological processes associated with large-scale movements of the Earth's crust (tectonic plates).<ref name="Stanley">Template:Cite book</ref> Folding, faulting, volcanic activity, igneous intrusion and metamorphism can all be parts of the orogenic process of mountain building.<ref name="Twiss">Template:Cite book</ref> The formation of mountains is not necessarily related to the geological structures found on it.<ref>Template:Cite book</ref>
From the late 18th century until its replacement by plate tectonics in the 1960s, geosyncline theory was used to explain much mountain-building.<ref>{{#invoke:citation/CS1|citation |CitationClass=web }}</ref> The understanding of specific landscape features in terms of the underlying tectonic processes is called tectonic geomorphology, and the study of geologically young or ongoing processes is called neotectonics.<ref name=Stuwe>Template:Cite book</ref>Template:Clarify
Types of mountainsEdit
Template:See also There are five main types of mountains: volcanic, fold, plateau, fault-block, and dome. A more detailed classification useful on a local scale predates plate tectonics and adds to these categories.<ref name=Goudie>Template:Cite book</ref>
Volcanic mountainsEdit
Movements of tectonic plates create volcanoes along the plate boundaries, which erupt and form mountains. A volcanic arc system is a series of volcanoes that form near a subduction zone where the crust of a sinking oceanic plate melts and drags water down with the subducting crust.<ref name=Butz>Template:Cite book</ref>
Most volcanoes occur in a band encircling the Pacific Ocean (the Pacific 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 are composite cones or stratovolcanoes and shield volcanoes.<ref name=Gerrard1>Template:Cite book</ref><ref name=Decker>Template:Cite book </ref>
A shield volcano has a gently sloping cone because of the low viscosity of the emitted material, primarily basalt. Mauna Loa is the classic example, with a slope of 4°-6°. (The relation between slope and viscosity falls under the topic of angle of repose.<ref name=Holmes&Duff>Template:Cite book</ref>) A composite volcano or stratovolcano has a more steeply rising cone (33°-40°),<ref name=transactions>Template:Cite book</ref> because of the higher viscosity of the emitted material, and eruptions are more violent and less frequent than for shield volcanoes. Examples include Vesuvius, Kilimanjaro, Mount Fuji, Mount Shasta, Mount Hood and Mount Rainier.<ref name=Todd>Template:Cite book</ref>
Fold mountainsEdit
When plates collide or undergo subduction (that is, ride one over another), the plates tend to buckle and fold, 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 or orogenesis. Examples are the Balkan Mountains, the Jura and the Zagros mountains.<ref name=Hatcher>Template:Cite book</ref>
Block mountainsEdit
When a fault block is raised or tilted, a block mountain can result.<ref name=Ryan>Template:Cite book</ref> Higher blocks are called horsts, and troughs are called grabens. 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 the Sierra Nevada range, where delamination 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.<ref name=Gerrard2>Template:Cite book</ref><ref name="delamination_lee">Template:Cite journal</ref>
Another example is the Rila–Rhodope massif in Bulgaria, including the well defined horsts of Belasitsa (linear horst), Rila mountain (vaulted domed shaped horst) and Pirin mountain—a horst forming a massive anticline situated between the complex graben valleys of the Struma and Mesta rivers.<ref name="Geographic Dictionary of Bulgaria 368">Template:Cite book</ref><ref name="dimitrova53">Template:Cite book</ref><ref>Template:Cite book</ref>
Uplifted passive marginsEdit
Unlike orogenic mountains there is no widely accepted geophysical model that explains elevated passive continental margins such as the Scandinavian Mountains, eastern Greenland, the Brazilian Highlands, or Australia's Great Dividing Range.<ref>{{#invoke:citation/CS1|citation |CitationClass=web }}</ref><ref name=Greenetal2013>Template:Cite journal</ref> Different elevated passive continental margins most likely share the same mechanism of uplift. This mechanism is possibly related to far-field stresses in Earth's lithosphere. According to this view elevated passive margins can be likened to giant anticlinal lithospheric folds, where folding is caused by horizontal compression acting on a thin to thick crust transition zone (as are all passive margins).<ref>Template:Cite journal</ref><ref>Løseth and Hendriksen 2005</ref>
ModelsEdit
Hotspot volcanoesEdit
Hotspots are supplied by a magma source in the Earth's mantle called a mantle plume. Although originally attributed to a melting of subducted oceanic crust, recent evidence belies this connection.<ref name=Stoffers>Template:Cite book</ref> The mechanism for plume formation remains a research topic.
Fault blocksEdit
Several movements of the Earth's crust that lead to mountains are associated with faults. 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 the rheology of the layers and the forces of isostasy. Early bent plate models predicting fractures and fault movements have evolved into today's kinematic and flexural models.<ref name=Watts>Template:Cite book</ref><ref name=Weissel>Template:Cite book</ref>
See alsoEdit
- Template:Annotated link
- Template:Annotated link
- Template:Annotated link
- Template:Annotated link
- Template:Annotated link