Editing Alps (section)

== Geology and orogeny ==
{{main|Alpine orogeny|Geology of the Alps}}

Important geological concepts were established as naturalists began studying the rock formations of the Alps in the 18th century. In the mid-19th century, the now-defunct idea of [[geosyncline]]s was used to explain the presence of "folded" mountain chains. This theory was replaced in the mid-20th century by the theory of [[plate tectonics]].<ref name="Graciansky1ff" />

[[File:Nante d'arpanaz.jpg|thumb|upright=1.15|The geologic [[Fold (geology)|folding]] seen at the Arpenaz waterfall, shown here in a mid-18th-century drawing, was noted by 18th-century geologists.<ref name="Graciansky5">Graciansky (2011), 5</ref>]]

The formation of the Alps (the [[Alpine orogeny]]) was an episodic process that began about 300&nbsp;million years ago.<ref>Shoumatoff (2001), 35</ref> In the [[Paleozoic]] Era the [[Pangaea]]n [[supercontinent]] consisted of a single [[tectonic plate]]; it broke into separate plates during the [[Mesozoic]] Era and the [[Tethys Ocean|Tethys]] sea developed between [[Laurasia]] and [[Gondwana]] during the [[Jurassic]] Period.<ref name="Graciansky1ff">Graciansky (2011), 1–2</ref> The Tethys was later squeezed between colliding plates causing the formation of mountain ranges called the [[Alpide belt]], from [[Gibraltar]] through the [[Himalayas]] to [[Indonesia]]—a process that began at the end of the [[Mesozoic]] and continues into the present. The formation of the Alps was a segment of this orogenic process,<ref name="Graciansky1ff" /> caused by the collision between the [[African Plate|African]] and the [[Eurasian Plate|Eurasian]] plates<ref name="Gerrard9" /> that began in the late [[Cretaceous]] Period.<ref name="Gerrard16">Gerrard, (1990), 16</ref>

Under extreme [[compressive stress]]es and pressure, marine [[sedimentary rock]]s were uplifted, forming characteristic recumbent [[Fold (geology)|folds]], and [[thrust fault]]s.<ref>''Earth'' (2008), 142</ref> As the rising peaks underwent erosion, a layer of marine [[flysch]] sediments was deposited in the [[foreland basin]], and the sediments became involved in younger folds as the orogeny progressed. Coarse sediments from the continual uplift and erosion were later deposited in [[Molasse basin|foreland areas]] north of the Alps.<ref name="Gerrard9">Gerrard, (1990), 9</ref> These regions in Switzerland and Bavaria are well-developed, containing classic examples of [[flysch]], which is [[sedimentary rock]] formed during mountain building.<ref name=Schmid102>Schmid (2004), 102</ref>

[[File:View from Mangart MC.jpg|thumb|left|upright=1.5|The dolomitic peaks of [[Triglav National Park]] in the [[Julian Alps]]]]

The Alpine orogeny occurred in ongoing cycles through to the Paleogene causing differences in folded structures, with a late-stage orogeny causing the development of the [[Jura Mountains]].<ref name=Schmid97>Schmid (2004), 97</ref> A series of tectonic events in the Triassic, Jurassic and Cretaceous periods caused different [[Palaeogeography|paleogeographic]] regions.<ref name=Schmid97/> The Alps are subdivided by different [[lithology]] (rock composition) and nappe structures according to the orogenic events that affected them.<ref name=Schmid93/> The geological subdivision differentiates the Western, Eastern Alps, and Southern Alps: the [[Helvetic nappes|Helveticum]] in the north, the [[Penninic nappes|Penninicum]] and [[Austroalpine nappes|Austroalpine system]] in the centre and, south of the Periadriatic Seam, the [[Southern Alps (geology)|Southern Alpine system]].<ref name=Schmid99/>

[[File:Matterhorn from Domhütte - 2.jpg|thumb|upright=1.15|Compressed metamorphosed Tethyan sediments and their oceanic basement are sandwiched between the tip of the [[Matterhorn]] (Italian-Swiss border), which consists of gneisses originally part of the African plate, and the base of the peak, which is part of the Eurasian plate.<ref name="Graciansky5"/>]]

According to geologist Stefan Schmid, because the Western Alps underwent a metamorphic event in the [[Cenozoic]] Era while the Austroalpine peaks underwent an event in the Cretaceous Period, the two areas show distinct differences in nappe formations.<ref name=Schmid97/> [[Flysch]] deposits in the Southern Alps of [[Lombardy]] probably occurred in the Cretaceous or later.<ref name=Schmid97/>

Peaks in France, Italy and Switzerland lie in the "Houillière zone", which consists of [[Basement (geology)|basement]] with sediments from the Mesozoic Era.<ref name=Schmid99>Schmid, 99</ref> High "massifs" with external sedimentary cover are more common in the Western Alps and were affected by [[Neogene]] Period [[Thin-skinned deformation|thin-skinned]] thrusting whereas the Eastern Alps have comparatively few high peaked massifs.<ref name=Schmid102/> Similarly the peaks in eastern Switzerland extending to western Austria (Helvetic nappes) consist of thin-skinned sedimentary folding that [[decollement|detached]] from former [[basement (geology)|basement]] rock.<ref name=Schmid103>Schmid (2004), 103</ref>

In simple terms, the structure of the Alps consists of layers of rock of European, African, and oceanic (Tethyan) origin.<ref name="Graciansky29ff">Graciansky (2011), 29</ref> The bottom nappe structure is of continental European origin, above which are stacked marine sediment nappes, topped off by nappes derived from the African plate.<ref name="Graciansky31">Graciansky (2011), 31</ref> The Matterhorn is an example of the ongoing orogeny and shows evidence of great folding. The tip of the mountain consists of [[gneiss]]es from the African plate; the base of the peak, below the glaciated area, consists of European basement rock. The sequence of Tethyan marine sediments and their oceanic basement is sandwiched between rock derived from the African and European plates.<ref name="Graciansky5"/>
{{wide image|Savine.JPG|750px|caption=[[Maurienne|Haute Maurienne]] (Ambin and Vanoise massifs) and its exposed crystalline basement made of high-pressure subduction rocks such as [[blueschist]] and [[quartzite|metaquartzite]] (picture taken at {{convert|2400|m|disp=or}})}}{{clear}}
The core regions of the Alpine orogenic belt have been folded and fractured in such a manner that erosion produced the characteristic steep vertical peaks of the [[Swiss Alps]] that rise seemingly straight out of the foreland areas.<ref name="Gerrard16"/> Peaks such as Mont Blanc, the Matterhorn, and high peaks in the Pennine Alps, the Briançonnais, and [[Hohe Tauern]] consist of layers of rock from the various orogenies including exposures of basement rock.<ref>Beattie (2006), 6–8</ref>

Due to the ever-present geologic instability, earthquakes continue in the Alps to this day.<ref>{{Cite web |url=http://www.seismo.ethz.ch/en/knowledge/earthquake-country-switzerland/earthquakes-and-the-alps/ |title=SED &#124; Earthquakes and the Alps |access-date=February 2, 2019 |archive-date=February 3, 2019 |archive-url=https://web.archive.org/web/20190203030400/http://www.seismo.ethz.ch/en/knowledge/earthquake-country-switzerland/earthquakes-and-the-alps/ |url-status=live }}</ref> Typically, the largest earthquakes in the alps have been between magnitude 6 and 7 on the Richter scale.<ref>{{Cite web |url=http://www.seismo.ethz.ch/static/100j/snapshot05/sn05_gal3_EN.html |title=The largest earthquakes in the Alps |access-date=February 2, 2019 |archive-date=February 2, 2019 |archive-url=https://web.archive.org/web/20190202212340/http://www.seismo.ethz.ch/static/100j/snapshot05/sn05_gal3_EN.html |url-status=live }}</ref> [[Geodesy|Geodetic]] measurements show ongoing topographic uplift at rates of up to about 2.5&nbsp;mm per year in the North, Western and Central Alps, and at ~1&nbsp;mm per year in the Eastern and South-Western Alps.<ref name="Sternai-2019">{{Cite journal |last1=Sternai |first1=Pietro |last2=Sue |first2=Christian |last3=Husson |first3=Laurent |last4=Serpelloni |first4=Enrico |last5=Becker |first5=Thorsten W. |last6=Willett |first6=Sean D. |last7=Faccenna |first7=Claudio |last8=Di Giulio |first8=Andrea |last9=Spada |first9=Giorgio |last10=Jolivet |first10=Laurent |last11=Valla |first11=Pierre |last12=Petit |first12=Carole |last13=Nocquet |first13=Jean-Mathieu |last14=Walpersdorf |first14=Andrea |last15=Castelltort |first15=Sébastien |date=March 2019 |title=Present-day uplift of the European Alps: Evaluating mechanisms and models of their relative contributions |url=https://doi.org/10.1016/j.earscirev.2019.01.005 |journal=Earth-Science Reviews |volume=190 |pages=589–604 |doi=10.1016/j.earscirev.2019.01.005 |bibcode=2019ESRv..190..589S |hdl=10281/229017 |s2cid=96447591 |issn=0012-8252 |hdl-access=free}}</ref> The underlying mechanisms that jointly drive the present-day uplift pattern are the isostatic rebound due to the melting of the last glacial maximum ice-cap or long-term erosion, detachment of the Western Alpine subducting slab, mantle convection as well as ongoing horizontal convergence between Africa and Europe, but their relative contributions to the uplift of the Alps are difficult to quantify and likely to vary significantly in space and time.<ref name="Sternai-2019" />