Editing Alps (section)

== Glaciers ==
{{see also|List of glaciers in Switzerland}}
[[File:Illustration_of_the_Glacier_System_of_the_Alps_by_Alexander_Keith_Johnston_1848.png|thumb|upright=1.6|right|This illustration of the glacier systems of the [[Mont Blanc massif]] by [[Alexander Keith Johnston (1804–1871)|Alexander Keith Johnston]] was first published 1848 in ''The Physical Atlas''.]]
In the [[Miocene]] Epoch the mountains underwent severe erosion because of glaciation,<ref name="Gerrard16" /> which was noted in the mid-19th century by naturalist [[Louis Agassiz]] who presented a paper proclaiming the Alps were covered in ice at various intervals—a theory he formed when studying rocks near his [[Neuchâtel]] home which he believed originated to the west in the Bernese Oberland. Because of his work he came to be known as the "father of the ice-age concept" although other naturalists before him put forth similar ideas.<ref name="Shoumatoff63ff">Shoumatoff (2001), 63–68</ref>

[[File:Aletschgebiet aus dem Flugzeug.jpg|thumb|left|[[Louis Agassiz]]'s studies of the [[Unteraar Glacier]] in the 1840s showed that it moved at {{cvt|100|m|0}} per year.<ref name="Shoumatoff63ff" />]]

Agassiz studied glacier movement in the 1840s at the [[Unteraar Glacier]] where he found the glacier moved {{cvt|100|m|0}} per year, more rapidly in the middle than at the edges. His work was continued by other scientists and now a permanent laboratory exists inside a glacier under the [[Jungfraujoch]], devoted exclusively to the study of Alpine glaciers.<ref name="Shoumatoff63ff" />

Glaciers pick up rocks and sediment with them as they flow. This causes erosion and the formation of valleys over time. The [[Inn (river)|Inn]] valley is an example of a valley carved by glaciers during the [[Quaternary glaciation|ice ages]] with a typical terraced structure caused by erosion. Eroded rocks from the most recent ice age lie at the bottom of the valley while the top of the valley consists of erosion from earlier ice ages.<ref name="Shoumatoff63ff" /> Glacial valleys have characteristically steep walls (reliefs); valleys with lower reliefs and [[Scree|talus slopes]] are remnants of glacial troughs or previously infilled valleys.<ref name="Gerrard132">Gerrard, (1990), 132</ref> [[Moraine]]s, piles of rock picked up during the movement of the glacier, accumulate at edges, centre, and the terminus of glaciers.<ref name="Shoumatoff63ff" />

[[File:Jungfraujoch img 3699.jpg|thumb|The Sphinx Tunnel connecting [[Jungfraujoch railway station]] to the [[Sphinx Observatory]], through a glacier at the [[Jungfraujoch]]]]

Alpine glaciers can be straight rivers of ice, long sweeping rivers, spread in a fan-like shape (Piedmont glaciers), and curtains of ice that hang from vertical slopes of the mountain peaks. The stress of the movement causes the ice to break and crack loudly, perhaps explaining why the mountains were believed to be home to dragons in the medieval period. The cracking creates unpredictable and dangerous [[crevasse]]s, often invisible under new snowfall, which causes the greatest danger to mountaineers.<ref name="Shoumatoff71ff"/>

Glaciers end in ice caves (the [[Rhône Glacier]]), by trailing into a lake or river, or by shedding snowmelt on a meadow. Sometimes a piece of glacier will detach or break resulting in flooding, property damage, and loss of life.<ref name="Shoumatoff71ff">Shoumatoff (2001), 71–72</ref>

High levels of precipitation cause the glaciers to descend to [[permafrost]] levels in some areas whereas in other, more arid regions, glaciers remain above about the {{cvt|3500|m|0}} level.<ref name="Gerrard78">Gerrard, (1990), 78</ref> The {{cvt|1817|km2}} of the Alps covered by glaciers in 1876 had shrunk to {{cvt|1342|km2}} by 1973, resulting in decreased river run-off levels.<ref name="Gerrard108">Gerrard, (1990), 108</ref> Forty percent of the glaciation in Austria has disappeared since 1850, and 30% of that in Switzerland.<ref>Ceben (1998), 38</ref>

Although the Alpine topography shows marked glacial morphologies,<ref>{{Cite journal |last1=Sternai |first1=P. |last2=Herman |first2=F. |last3=Fox |first3=M. R. |last4=Castelltort |first4=S. |date=2011-07-13 |title=Hypsometric analysis to identify spatially variable glacial erosion |journal=Journal of Geophysical Research |language=en |volume=116 |issue=F3 |pages=F03001 |doi=10.1029/2010JF001823 |bibcode=2011JGRF..116.3001S |issn=0148-0227 |doi-access=free}}</ref> the mechanisms by which glacial reshaping occurs are unclear. [[Computer simulation|Numerical modeling]] suggests that glacial erosion propagates from low elevations to high elevations leading to an early increase of local relief followed by lowering of the mean orogen elevation.<ref>{{Cite journal |last1=Sternai |first1=Pietro |last2=Herman |first2=Frédéric |last3=Valla |first3=Pierre G. |last4=Champagnac |first4=Jean-Daniel |date=2013-04-15 |title=Spatial and temporal variations of glacial erosion in the Rhône valley (Swiss Alps): Insights from numerical modeling |url=https://hal-insu.archives-ouvertes.fr/insu-00853433/file/Sternai-EPSL-2013.pdf |journal=Earth and Planetary Science Letters |language=en |volume=368 |pages=119–131 |doi=10.1016/j.epsl.2013.02.039 |bibcode=2013E&PSL.368..119S |s2cid=14687787 |issn=0012-821X}}</ref>