Amountain chain is a row of highmountain summits, a linear sequence of interconnected or related mountains,[1] or a contiguous ridge of mountains within a largermountain range. The term is also used for elongatedfold mountains with several parallel chains ("chain mountains").
While in mountain ranges, the term mountain chain is common, in hill ranges a sequence ofhills tends to be referred to aridge orhill chain.
Elongated mountain chains occur most frequently in theorogeny of fold mountains, (that are folded by lateral pressure), andnappe belts (where a sheetlike body of rock has been pushed over another rock mass). Other types of range such ashorst ranges,fault block mountain ortruncated uplands rarely form parallel mountain chains. However, if a truncated upland is eroded into a hightable land, the incision of valleys can lead to the formations of mountain or hill chains.
The chain-like arrangement of summits and the formation of long, jaggedmountain crests – known in Spanish assierras ("saws") – is a consequence of their collective formation bymountain building forces. The often linear structure is linked to the direction of these thrust forces and the resultingmountain folding which in turn relates to thefault lines in the upper part of theEarth's crust, that run between the individual mountain chains. In thesefault zones, the rock, which has sometimes been pulverised, is easily eroded, so that largeriver valleys are carved out. These, so calledlongitudinal 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. theCordilleras) to produce roughly parallel chains is due to their rock structure and the propulsive forces ofplate tectonics. The uplifted rock masses are either magmaticplutonic rocks, easily shaped because of their higher temperature, orsediments ormetamorphic rocks, which have a less robust structure, that are deposited in thesynclines. 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. Theoverthrust folds of anappe belt (e.g. theCentral 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 continuousarêtes or ridges that follow thestrike 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 formwater 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 orsummit chains. Between them, notches were formed that, depending onaltitude and rock-type, form knife-edgedcols or gentlermountain passes andsaddles.
Nappe or fold mountains, with their roughly parallel mountain chains, generally have a commongeological age, but may consist of various types ofrock. For example, in the Central Alps,granitic rocks,gneisses and metamorphicslate are found, while to the north and south, are theLimestone Alps. TheNorthern Limestone Alps are, in turn, followed by softflysch mountains and themolasse zone.
The type of rock influences the appearance of the mountain ranges very markedly, becauseerosion leads to very different topography depending on thehardness of the rock and itspetrological structure. In addition to height and climate, other factors are thelayering of the rock, itsgradient andaspect, the types ofwaterbody and the lines ofdislocation. For hard rock massifs, rugged rock faces (e.g. in theDolomites) and mightyscree slopes are typical. By contrast, flysch or slate forms gentler mountain shapes andkuppen or domed mountaintops, because the rock is not porous, but easily shaped.
