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{{Infobox UNESCO World Heritage Site
| WHS           = Glarus Overthrust
| image         = Glarus Thrust Fault in Switzerland 2018.jpg
| image_upright = 1.2
| caption       = The [[Tschingelhörner]] on the border of [[Cantons of Switzerland|Swiss cantons]] [[Glarus (canton)|Glarus]] and [[Graubünden]]. The Glarus thrust can be seen as a horizontal line in the cliffs.
| location      = [[Switzerland]]
| part_of       = Swiss Tectonic Arena [[Sardona]]
| criteria      = {{UNESCO WHS type|(viii)}}(viii)
| ID            = 1179
| coordinates   = {{coord|46|55|N|9|15|E|region:CH_type:landmark|display=inline,title}}
| year          = 2008
| website       = {{URL|http://www.glarusoverthrust.org}}
| locmapin      = Switzerland
| map_caption   = 
}}
[[File:Picswiss GL-12-03.jpg|thumb|upright=1.2|[[Martinsloch]]]]
The '''Glarus thrust''' ({{langx|de|Glarner Überschiebung}}) is a major [[thrust fault]] in the [[Alps]] of eastern [[Switzerland]]. Along the thrust the [[Helvetic nappes]] were thrust more than 100&nbsp;km to the north over the external [[Aarmassif]] and [[Infrahelvetic complex]]. The thrust forms the contact between older (Helvetic) [[Permian|Permo]]-[[Triassic]] rock layers of the [[Verrucano group]] and younger (external) [[Jurassic]] and [[Cretaceous]] [[limestone]]s and [[Paleogene]] [[flysch]] and [[molasse]].

The Glarus thrust [[outcrop|crops out]] over a relatively large area in the [[Cantons of Switzerland|cantons]] [[Glarus (canton)|Glarus]], [[Canton of St. Gallen|St. Gallen]] and [[Graubünden]], due to its horizontal orientation and the high local [[relief]]. Famous outcrops include those at [[Lochsite]] near [[Glarus]] (the town) and in a mountain cliff called ''[[Tschingelhörner]]'' between [[Elm, Switzerland|Elm]] and [[Flims]] (in the same cliff is a natural hole called the [[Martinsloch]]).

== World Heritage ==
Thrust faults of this kind are not uncommon in many mountain chains around the world, but the Glarus thrust is a well accessible example and has as such played an important role in the development of [[geology|geological]] knowledge on [[orogenesis|mountain building]]. For this reason the area in which the thrust is found was declared a [[geotope]], a geologic [[UNESCO]] [[World Heritage Site]], under the name "Swiss Tectonic Arena Sardona." The area of this "tectonic arena" encompasses 32,850 [[hectare]]s of mainly mountainous landscape in 19 communities between the [[Surselva]], [[Linth]]tal and [[Walensee]]. In the arena are a number of peaks higher than 3000 meters, such as [[Piz Sardona|Surenstock]] (its [[Romansh language|Romansh]] name is ''Piz Sardona'', from which the name comes), [[Ringelspitz]] and [[Pizol]].

In 2006, the [[Switzerland|Swiss]] government made a first proposal to declare the region World Heritage to the [[International Union for Conservation of Nature]] (IUCN). The IUCN then did not find the area to have an extraordinary or universal value and denied the proposal. The Swiss made a new, this time successful proposal in March 2008. The region was declared a World Heritage Site in July 2008, because "the area displays an exceptional example of mountain building through continental collision and features excellent geological sections through [[tectonic]] thrust."<ref>[https://whc.unesco.org/en/list/1179 Swiss Tectonic Arena Sardona – UNESCO World Heritage Centre]</ref>

The [[American Museum of Natural History]] in [[New York City|New York]] exposes a full-scale reconstruction of the Glarus thrust.<ref>{{usurped|1=[http://www.glarusoverthrust.org/inhalt.asp?fHigherChapter_ID=150&fChapters_id=150&fSubChapters_id=153&fTemplatefile=inhalt.asp&ID_Postcards=&fPassword=# geopark association]}}</ref>

[[File:Escher Martinsloch.jpg|thumb|upright=1.2|Drawing of the Glarus thrust in the Tschingelhörner by [[Hans Conrad Escher von der Linth]], 1812.]]
[[File:Glarner Hauptüberschiebung am Segnes 2008 SE.jpg|thumb|upright=1.2|Glarus thrust fault at Piz Segnes]]

== History ==
The first [[natural history|naturalist]] to examine the Glarus thrust was [[Hans Conrad Escher von der Linth]] (1767–1823). Escher von der Linth discovered that, contradictory to [[Nicholas Steno|Steno's]] [[law of superposition]], older rocks are on top of younger ones in certain [[outcrop]]s in Glarus. His son [[Arnold Escher von der Linth]] (1807–1872), the first professor in geology at the [[ETH Zurich|ETH at Zürich]], mapped the structure in more detail and concluded that it could be a huge [[Thrust (physics)|thrust]]. At the time, most geologists still accepted the theory of [[geosyncline]]s, which states that mountains are formed by vertical movements within the Earth's [[crust (geology)|crust]]. Escher von der Linth had therefore difficulty with explaining the size of the thrust fault. In 1848, he invited the British geologist [[Roderick Murchison]], an international authority, to come and look at the structure. Murchison was familiar with larger thrust faults in Scotland and agreed with Escher's interpretation. However, Escher himself felt insecure about his idea and when he published his observations in 1866 he instead interpreted the Glarus thrust as two large overturned narrow [[anticline]]s. This hypothesis was rather absurd, as he admitted himself in private.

Escher's successor as professor at Zürich, [[Albert Heim]] (1849–1937), initially stuck to his predecessor's interpretation of two anticlines. However, some geologists favoured the idea of a thrust. One of them was [[Marcel Alexandre Bertrand]] (1847–1907), who interpreted the structure as a thrust in 1884, after reading Heims observations.<ref>{{cite journal |author-link=Marcel Alexandre Bertrand|last=Bertrand |first1= M.|year=1884|title=Rapports de structure des Alpes de Glaris et du bassin houiller du Nord | journal=Société Géologique de France Bulletin |series= 3rd |volume= 12 |pages= 318–330 }}</ref> Bertrand was familiar with the [[Faille du Midi]] ([[Variscan orogeny]]), a large thrust fault in the [[Belgium|Belgian]] [[Ardennes]]. Meanwhile, British geologists began to recognize the nature of thrust faults in the [[Scottish Highlands]]. In 1883, [[Archibald Geikie]] accepted that the Highlands are a thrust system.<ref>{{cite journal |author-link=Archibald Geikie|last=Geikie |first= A.|year=1883| title=On the Supposed Pre-Cambrian Rocks of St. David's |journal=Quarterly Journal of the Geological Society  | volume=39 |issue=1–4 |pages=261–333 | doi = 10.1144/GSL.JGS.1883.039.01-04.21 }}</ref> Swiss geologists [[Hans Schardt]] and [[Maurice Lugeon]] then discovered in 1893 that in western Switzerland, Jurassic rock layers are on top of younger molasse too, and argued that the structure of the Alps is a large [[nappe stack|stack]] of [[nappe]]s, large sheets of rock that had been thrust on top of each other.<ref>{{cite journal | last=Schardt |first= H. | year=1893 | title=Sur l’origine des Préalpes romandes | journal= Eclogae geologicae Helvetiae |volume=4 |pages= 129–142 }}</ref> At the turn of the century, Heim was also convinced of the new theory. He and other Swiss geologists now started mapping the nappes of Switzerland in more detail. From that moment on, geologists began recognizing large thrusts in many mountain chains around the world.

However, it was still not understood where the huge [[force]]s that moved the [[nappe]]s came from. Only with the arrival of [[plate tectonics|plate tectonic theory]] in the 1950s an explanation was found. In plate tectonics, the horizontal movement of [[Plate tectonics|tectonic plates]] over the Earth's soft [[asthenosphere]] causes horizontal forces within the [[Crust (geology)|crust]]. Presently, geologists explain the formation of most [[mountain chain]]s by the [[convergent boundary]] evolving between [[Plate tectonics|tectonic plates]] accompanied by a [[subduction]] process in which the heavier plate dives beneath the less dense plate and sinks into the [[Earth's mantle]].

{{wide image|Glarus Thrust Fault at Piz Segnes.JPG|600px|Glarus Thrust fault at Piz Segnes}}

== See also ==
* [[Nappe]]
* [[Thrust fault]]
* [[Geology of the Alps]]
* [[Geology of Scotland]] (Scottish thrust faults)
* [[Orogeny]]

== Notes and references ==
{{Reflist|2}}

== Literature ==
* {{cite web | title=Glarus, Alpine Nappes | website=The Geological  Society | url=https://www.geolsoc.org.uk/Policy-and-Media/Outreach/Plate-Tectonic-Stories/Ben-Arnaboll/Glarus | access-date=2024-05-28}}

* {{cite journal|last=Franks|first=Sibylle|author2=[[Rudolf Trümpy]]|title=The Sixth International Geological Congress: Zürich, 1894|journal=Journal of International Geoscience|publisher=International Union of Geological sciences|date=September 2005|series=Episodes|volume=28|issue=3|pages=187–192|url=http://www.episodes.org/backissues/283/187-Franks.pdf|format=PDF|access-date=2008-07-10|url-status=dead|archive-url=https://web.archive.org/web/20110928120448/http://www.episodes.org/backissues/283/187-Franks.pdf|archive-date=2011-09-28}}

* {{cite journal | last1=Poulet | first1=Thomas | last2=Veveakis | first2=Manolis | last3=Herwegh | first3=Marco | last4=Buckingham | first4=Thomas | last5=Regenauer‐Lieb | first5=Klaus | date=2014-10-28 | title=Modeling episodic fluid‐release events in the ductile carbonates of the Glarus thrust | journal=Geophysical Research Letters | volume=41 | issue=20 | pages=7121–7128 | issn=0094-8276 | url=https://agupubs.onlinelibrary.wiley.com/doi/pdfdirect/10.1002/2014GL061715 | format=PDF | doi=10.1002/2014GL061715 | doi-access=free| hdl=1959.4/unsworks_37154 | hdl-access=free }}

* {{cite journal | last1=Badertscher | first1=Nicolas P. | last2=Beaudoin | first2=Georges | last3=Therrien | first3=René | last4=Burkhard | first4=Martin | date=2002 | title=Glarus overthrust: A major pathway for the escape of fluids out of the Alpine orogen | journal=Geology | volume=30 | issue=10 | page=875–878 | issn=0091-7613 | doi=10.1130/0091-7613(2002)030<0875:GOAMPF>2.0.CO;2}}

* {{cite journal | last1=Herwegh | first1=Marco | last2=Hürzeler | first2=Jean-Pierre | last3=Pfiffner | first3=O. Adrian | last4=Schmid | first4=Stefan M. | last5=Abart | first5=Rainer | last6=Ebert | first6=Andreas | date=2008 | title=The Glarus thrust: Excursion guide and report of a field trip of the Swiss Tectonic Studies Group (Swiss Geological Society, 14–16. 09. 2006) | journal=[[Swiss Journal of Geosciences]] | volume=101 | issue=2 | pages=323–340 | issn=1661-8726 | doi=10.1007/s00015-008-1259-z}}

== External links ==
{{Commons category|Glarner Hauptüberschiebung|Glarus thrust}}
{{Commons category|Martinsloch}}

* {{cite web | title=GeoViewer Kanton Glarus | website=GeoViewer Kanton Glarus | url=https://map.geo.gl.ch/?l=ch.gl.basemaps.kantonsmaske%5B40%5D&bl=pixelkarte&t=default&c=2725000%2C1206500&s=200000 | access-date=2024-05-28}}

{{World Heritage Sites in Switzerland}}
{{Portal bar|Switzerland}}

[[Category:Glarus thrust| ]]
[[Category:Geology of the Alps]]
[[Category:World Heritage Sites in Switzerland]]
[[Category:Flims]]
[[Category:Tourist attractions in Switzerland]]
[[Category:Geography of the canton of Glarus]]
[[Category:Geography of Graubünden]]
[[Category:Geography of the canton of St. Gallen]]
[[Category:Glarus–Graubünden border]]
[[Category:Protected areas of the Alps]]