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Glarus Thrust

Switzerland

Famous view of Tschingelhörner with Martin’s Hole. The Glarus thrust is visible as a line along the cliff where the rock changes color.

Famous view of Tschingelhörner with Martin’s Hole. The Glarus thrust is visible as a line along the cliff where the rock changes color.

Geological Period

Permian to Quaternary

Main geological interest

Tectonics
History of geosciences

Location

Cantons of Glarus,
St. Gallen and Grisons, Switzerland
46°55’22”N, 009°15’05”E

Famous view of Tschingelhörner with Martin’s Hole. The Glarus thrust is visible as a line along the cliff where the rock changes color.

An exceptional and dramatic display of mountain building through continental collision with phenomenal outcrops in an alpine mountain landscape.

Thrust faults represent unique features in collisional orogens, where through the collision of continental plates the crust is thickened and uplifted to form mountain ranges. The stacking of nappes along thrusts is one of the main mechanisms responsible for thickening of the upper crust, uplift, erosion and thereby forming of a mountain relief. In this way the Glarus thrust is a witness of processes that take place at great depths within the Earths’ crust in all major mountain ranges (Pfiffner et al., 2006; Pfiffner and Schmid, 2008). The scenic exposure and the numerous outcrops of the thrust surface inspired generations of geologists to study its secrets (Westermann, 2009).

The domelike Glarus thrust, here visualized as a grid structure crosscutting the mountain ranges for dozens of kilometers.

The domelike Glarus thrust, here visualized as a grid structure crosscutting the mountain ranges for dozens of kilometers.

  • Geological description

The Glarus thrust is a unique structure which can be followed over several kilometers and numerous outcrops in eastern Switzerland. It is visible as a baffling, seemingly perfect geometric surface, cutting through the mountain landscape and cropping out as a sharp line along cliffs.
The Glarus thrust formed during Oligocene to Miocene times and put older rocks onto younger rocks in the entire region. The minimal displacement along this large-scale shear zone is estimated to be more than 50 kilometers.
The large Glarus thrust surface once formed as a ramp reaching some 10–15 kilometers deep in the upper crust. It was exposed following rapid uplift rates of more than 1 mm/year and ensuing fast erosion rates such that rivers cut deep valleys, some of which were further deepened and widened by glaciers. As a result, a unique clear three-dimensional visibility of the Glarus thrust in a mountain landscape emerged.
Erosion further resulted in several klippen of Permian Verrucano rocks sitting on top of much younger rocks. In some instances, the age difference between hanging wall and footwall rocks across the Glarus thrust is more than 200 million years, observed over a distance of only a few centimeters (Herwegh et al., 2008; Schmid, 1975).

  • Scientific research and tradition

The observation that older rocks lie above younger rocks puzzled the early workers in the 19th century. Different explanations for this observation led to heated debates and inspired scientists until the present. Discussions incited the question how mountain ranges form and -besides tectonics- opened research on metamorphism, geochemistry and geomorphology (Westermann, 2009).

Evolution of the Glarus thrust. Permian Verrucano was moved onto much younger rocks and simultaneous erosion and uplift made it visible in a mountain relief. Pfiffner, O.A., 2019, Landschaften und Geologie der Schweiz. Haupt Verlag, Bern, 358 pp.

Evolution of the Glarus thrust. Permian Verrucano was moved onto much younger rocks and simultaneous erosion and uplift made it visible in a mountain relief. Pfiffner, O.A., 2019, Landschaften und Geologie der Schweiz. Haupt Verlag, Bern, 358 pp.

  • Reference

Herwegh, M. et al. (2008) ‘The Glarus thrust: Excursion guide and report of a field trip of the Swiss Tectonic Studies Group (Swiss Geological Society, 14.-16. 09. 2006)’, Swiss Journal of Geosciences, 101, pp. 323–340. Available at: https://doi.org/10.1007/s00015-008-1259-z.

Pfiffner, O.A., Burkhard, M. and Schmid, S.M. (2006) Comparative study on thrust faults. UNESCO-World Heritage TektonicArena Sardona, p. 129. Available at: https://data.unesco-sardona.ch/forschen/wissenschaftliche-publikationen/.

Pfiffner, O.A. and Schmid, S.M. (2008) Supplement to the Comparative study on thrust faults: The Glarus overthrust. UNESCO-World Heritage TektonicArena Sardona. Available at: https://data.unesco-sardona.ch/forschen/wissenschaftliche-publikationen/.

Schmid, S. (1975) ‘The Glarus overthrust : field evidence and mechanical model The Glarus Overthrust: Field Evidence and Mechanical Model’, Eclogae Geologicae Helvetiae, 68, pp. 247–280. Available at: https://doi.org/10.5169/seals-164386.

Westermann, A. (2009) ‘Inherited Territories: The Glarus Alps, Knowledge Validation, and the Genealogical Organization of Nineteenth-Century Swiss Alpine Geognosy’, Science in Context, 22(3), pp. 439–461. Available at: https://doi.org/10.1017/S0269889709990081.

  • Author(s)

Thomas Buckingham.
UNESCO-World Heritage Swiss TectonicArena Sardona. Switzerland.

Adrian O. Pfiffner.
Professor Emeritus at Universität Bern. Switzerland.

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