Swiss Alps - Geology

Geology

The composition of the great tectonic units reflects the history of the formation of the Alps. The rocks from the Helvetic zone on the north and the Austroalpine nappes - Southern Alps on the south come originally from the European and African continent respectively. The rocks of the Penninic nappes belong to the former area of the Briançonnais microcontinent and the Tethys Ocean. The closure of the latter by subduction under the African plate (Piemont Ocean first and Valais Ocean later) preceded the collision between the two plates and the so-called alpine orogeny. The major thrust fault of the Tectonic Arena Sardona in the eastern Glarus Alps gives a visible illustration of mountain-building processes and was therefore declared a UNESCO World Heritage. Another fine example gives the Alpstein area with several visible upfolds of Helvetic zone material.

With some exceptions, the Alps north of Rhone and Rhine river are part of the Helvetic Zone and those on the south side are part of the Penninic nappes. The Austroalpine zone concerns almost only the Eastern Alps, with the notable exception of the Matterhorn.

The last glaciations greatly transformed Switzerland’s landscape. Many valleys of the Swiss Alps are U-shaped due to glacial erosion. During the maximum extension of the Würm glaciation (18,000 years ago) the glaciers completely covered the Swiss Plateau, before retreating and leaving remnants only in high mountain areas. In modern times the Aletsch Glacier in the western Bernese Alps is the largest and longest in the Alps, reaching a maximum depth of 900 metres at Konkordia. Along with the Fiescher and Aar Glaciers the region became a UNESCO World Heritage Site in 2001. An effect of the retreat of the Rhine Glacier some 10'000 years ago was the Flims Rockslide, the biggest still visible landslide apparently worldwide.