page_title: Orogeny
section_title: Relationship to mountain building
hierarchical_section_title: Orogeny / Physiography / Relationship to mountain building
caption_attribution_description: On February 6th 2003, astronauts aboard the International Space Station looked obliquely down at the steep eastern flank of California’s Sierra Nevada. Even from space the topography is impressive—the range drops nearly 11,000 feet from Mt. Whitney (under cloud, arrow), the highest mountain in the lower 48 states (14,494 ft), to the floor of Owens Valley (the elevation of the town of Lone Pine is 3,760 ft).
context_page_description: An orogeny is an event that leads to both structural deformation and compositional differentiation of the Earth's lithosphere at convergent plate margins. An orogen or orogenic belt develops when a continental plate crumples and is pushed upwards to form one or more mountain ranges; this involves a series of geological processes collectively called orogenesis.
  Orogeny is the primary mechanism by which mountains are built on continents. The word "orogeny" comes from Ancient Greek. Although it was used before him, the term was employed by the American geologist G.K. Gilbert in 1890 to describe the process of mountain-building as distinguished from epeirogeny.
context_section_description: Mountain formation occurs through a number of  mechanisms.
  Mountain complexes result from irregular successions of tectonic responses due to sea-floor spreading, shifting lithosphere plates, transform faults, and colliding, coupled and uncoupled continental margins.
  — Peter J Coney
  Large modern orogenies often lie on the margins of present-day continents; the Alleghenian (Appalachian), Laramide, and Andean orogenies exemplify this in the Americas. Older inactive orogenies, such as the Algoman, Penokean and Antler, are represented by deformed and metamorphosed rocks with sedimentary basins further inland.
  Areas that are rifting apart, such as mid-ocean ridges and the East African Rift, have mountains due to thermal buoyancy related to the hot mantle underneath them; this thermal buoyancy is known as dynamic topography. In strike-slip orogens, such as the San Andreas Fault, restraining bends result in regions of localized crustal shortening and mountain building without a plate-margin-wide orogeny. Hotspot volcanism results in the formation of isolated mountains and mountain chains that look as if they are not necessarily on present tectonic-plate boundaries, but they are essentially the product of plate tectonism.
  Regions can also experience uplift as a result of delamination of the orogenic lithosphere, in which an unstable portion of cold lithospheric root drips down into the asthenospheric mantle, decreasing the density of the lithosphere and causing buoyant uplift.  An example is the Sierra Nevada in California. This range of fault-block mountains experienced renewed uplift due to abundant magmatism after a delamination of the orogenic root beneath them.
  Finally, uplift and erosion related to epeirogenesis (large-scale vertical motions of portions of continents without much associated folding, metamorphism, or deformation) can create local topographic highs.
  Mount Rundle on the Trans-Canada Highway between Banff and Canmore provides a classic example of a mountain cut in dipping-layered rocks. Millions of years ago a collision caused an orogeny, forcing horizontal layers of an ancient ocean crust to be thrust up at an angle of 50–60°. That left Rundle with one sweeping, tree-lined smooth face, and one sharp, steep face where the edge of the uplifted layers are exposed.
caption: Sierra Nevada Mountains (a result of delamination) as seen from the International Space Station.
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