page_title: Mountain chain
section_title: Formation of parallel mountain chains
hierarchical_section_title: Mountain chain / Formation of parallel mountain chains
caption_attribution_description: Български: Пейзаж от национален парк „Централен Балкан”, БългарияEnglish: Central Balkan National Park This is a photo of a natural heritage site in Bulgaria, id: NP02
context_page_description: A mountain chain is a row of high mountain summits, a linear sequence of interconnected or related mountains, or a contiguous ridge of mountains within a larger mountain range. The term is also used for elongated fold mountains with several parallel chains.
  While in mountain ranges, the term mountain chain is common, in hill ranges a sequence of hills tends to be referred to a ridge or hill chain.
  Elongated mountain chains occur most frequently in the orogeny of fold mountains, and nappe belts. Other types of range such as horst ranges, fault block mountain or truncated uplands rarely form parallel mountain chains. However, if a truncated upland is eroded into a high table land, the incision of valleys can lead to the formations of mountain or hill chains.
context_section_description: The chain-like arrangement of summits and the formation of long, jagged mountain crests – known in Spanish as sierras ("saws") – is a consequence of their collective formation by mountain building forces. The often linear structure is linked to the direction of these thrust forces and the resulting mountain folding which in turn relates to the fault lines in the upper part of the earth's crust, that run between the individual mountain chains. In these fault zones, the rock, which has sometimes been pulverised, is easily eroded, so that large river valleys are carved out. These, so called longitudinal valleys reinforce the trend, during the early mountain building phase, towards the formation of parallel chains of mountains.
  The tendency, especially of fold mountains (e. g. the Cordilleras) to produce roughly parallel chains is due to their rock structure and the propulsive forces of plate tectonics. The uplifted rock masses are either magmatic plutonic rocks, easily shaped because of their higher temperature, or sediments or metamorphic rocks, which have a less robust structure, that are deposited in the synclines. As a result of orogenic movements, strata of folded rock are formed that are crumpled out of their original horizontal plane and thrust against one another. The longitudinal stretching of the folds takes place at right angles to the direction of the lateral thrusting. The overthrust folds of a nappe belt (e.g. the Central Alps) are formed in a similar way.
  Although the fold mountains, chain mountains and nappe belts around the world were formed at different times in the earth's history, all during their initial mountain building phases, they are nevertheless morphologically similar. Harder rock forms continuous arêtes or ridges that follow the strike of the beds and folds. The mountain chains or ridges therefore run approximately parallel to one another. They are only interrupted by short, usually narrow, transverse valleys, which often form water gaps. During the course of earth history, erosion by water, ice and wind carried away the highest points of the mountain crests and carved out individual summits or summit chains. Between them, notches were formed that, depending on altitude and rock-type, form knife-edged cols or gentler mountain passes and saddles.
caption: A view of the Balkan Mountains chain
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