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The Nappe Structure of the Alps

by Theresa König last modified 2008-02-19 15:09

The Nappe Structure of the Alps

At this scenic point you can see rocks originating from the African as well as from the European continent.  Here, rocks of different continents form the underground. These continents were separated by at least 2 small oceans the remnants of which can be found in the Alps at altitudes of up to 4,000 m above sea level and covering a distance of more than 2,000 kilometres. About 140 million years ago, during the Alpine orogeny the different units – the African plate, the lost micro-continents and the small oceans as well as the European platform – were stacked.

The impressive ridges of the Vandanser Steinwand and Zimba mountain, on the front left side of the valley as well as  the Davenna and the Hohe Frassen on the right form part of the Austro-alpine Northern Calcareous Alps originating from the African plate. To the right you can see the green slopes of the Hochgerach chain which belongs to the so called “Flyschzone” and which consists of deep-sea-sediments that were deposited in a small ocean. To the west, the rugged calcareous mountains on the western side of the Rhine-valley - part of the Säntis-group can be seen. They belong to the Helvetic nappes that originate from the European shelf. Finally you can see the green and hilly landscape to the north that is part of the Molasse zone. The Molasse-zone developed through the erosion of the rising Alps over the last 37 million years.

The deep cut into the nappe stack was made by the rivers Rhine and Ill. This cut offers a look into the deep structure of the mountain body. The ice-age glacier of the Ill and its melted snow and ice eroded the floor of the Walgau valley to 250 m below the present floor. The bedrock of the Rhine valley lies 300 m below sea level and 700 m below the present floor.
You can see the constrictions of the Walgau valley from both sides by the mountain ridges of the Northern Calcareous Alps to the north of Bludenz and the Flysch-ridge west of Schlins- Düns and also the Helvetic ridges south of Feldkirch.

The plate also shows the maximum level of the glacier during the climax of the Würm ice-age 18,000 to 20,000 years ago.

North of the village of Bürs you see the widely spread fan of the Schesa creek, which has meanwhile been densely populated. Since 1796 this fan has been deposited with 40,000.000 m³ of debris eroded and transported by the Schesa river. The catastrophic mud flows have destroyed buildings, roads, fields and meadows. Buildings and trees were buried up to 80 m under a mud flow.  Some of these buildings and trees were discovered and excavated in 1994 while quarrying for gravel and sand. To the south side of the village of Bürs, there are the steep walls of a petrified interglacial fan of the Alvir creek that flows through the Bürs gully. You can get more detailed information about the mud flows, the protective measures and the geology of the Schesa gully in the local museum in Bürserberg.


P04-1 The nappe structure of the alps.mp3

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