What is Orogeny?
[[File:Mtcook1600x1200.jpg|thumb|250px|[[Mount Cook]], [[New Zealand]]. It lies in the Southern Alps, the mountain range which runs the length of the [[South Island]]. New Zealand sits on top of the junction of two oceanic plates.]] [[File:Millook cliffs enh.jpg|thumb|250px|Even when mountains are worn down, the evidence is there in the remaining rocks. Millook, [[Cornwall]]]] '''Orogeny''' is the process of [[mountain]]-building. It takes place when two [[tectonic plate]]s come together. Orogens develop while a continental plate is crumpled and thickened to form [[mountain range]]s, and involve a great range of geological processes collectively called '''orogenesis'''.<ref name=Waltham>{{cite book |title=Foundations of engineering geology |author=Tony Waltham |page=20 |url=https://books.google.com/books?id=JGtIHJTXaI4C&pg=PA20 |isbn=978-0415469593 |publisher=Taylor & Francis |year=2009 |edition=3rd}}</ref><ref name=Vine>{{cite book |title=Global tectonics |author=Philip Kearey, Keith A. Klepeis, Frederick J. Vine |chapter-url=https://books.google.com/books?id=HYqZntfg25UC&pg=PA287 |page=287 |chapter=Chapter 10: Orogenic belts |isbn=978-1405107778 |year=2009 |publisher=Wiley-Blackwell |edition=3rd}}</ref> A [[convergent boundary]] is a frequent cause: *Where a continent rides over an oceanic plate (non-collisional): ** [[Andes]] in [[South America]] *Where two continental plates converge (collide): ** [[Alps]] ** [[Himalayas]] Another, less common cause is when a plate moves over a [[Hotspot (geology)|hot spot]] in the Earth's [[Mantle (geology)|mantle]]. Examples: *[[Hawaii]]an chain of islands *[[Yellowstone National Park]] There is a third process, called ''delamination''. Here an unstable portion of cold root of the [[lithosphere]] drips down into the mantle, decreasing the density of the lithosphere and causing buoyant uplift. Example: * The [[Sierra Nevada (US)|Sierra Nevada]] in California. Areas that are [[Rift (geology)|rift]]ing apart, such as [[mid-ocean ridge]]s and the East African Rift have mo