Glarus Thrust - History

History

The first naturalist to examine the Glarus thrust was Hans Conrad Escher von der Linth (1767–1823). Escher von der Linth discovered that, contradictory to Steno's law of superposition, older rocks are on top of younger ones in certain outcrops in Glarus. His son Arnold Escher von der Linth (1807–1872), the first professor in geology at the ETH at Zürich, mapped the structure in more detail and concluded that it could be a huge thrust. At the time, most geologists believed in the theory of geosynclines, which states that mountains are formed by vertical movements within the Earth's 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 Eschers 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 anticlines. This hypothesis was rather absurd, as he admitted himself in private.

Eschers successor as professor at Zürich, Albert Heim (1849–1937), initially stuck to his predecessors 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. Bertrand was familiar with the Faille du Midi (Variscan orogeny), a large thrust fault in the 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. 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 stack of nappes, large sheets of rock that had been thrusted on top of each other. 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 forces that moved the nappes came from. Only with the arrival of plate tectonic theory in the 1950s an explanation was found. In plate tectonics, the horizontal movement of tectonic plates over the Earth's soft asthenosphere causes horizontal forces within the crust. Presently, geologists believe most mountain chains are formed by convergent movements between tectonic plates.