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Geology of Val d’Hérens
Geology of the Val d'Hérens
Geology and glaciology centre
Introduction
This site presents in twelve concise, easy to understand chapters the geology of the Valais, essentially the south part of the Rhone and more specifically the Val d’Hérens.
Rocks and metamorphism
During the formation of the Alps the rocks from the mountains in Valais were brought thousands of metres underground and radically transformed.
Plate tectonics
The Alps are the result of a collision between the European and African plates provoked by the disappearance of the Alpine ocean under the African plate.
A rift in the Alps
The Alpine Ocean opened in the Early Jurassic when the super continent Pangea was fractured by a series of rifts, leaving visible traces in the Alps.
Reconstructing past geography
The Alpine and the Central Atlantic Ocean was the same ocean. Successive traces of the Atlantic mid-ocean ridge allow for the reconstruction of African and European plate movement over time.
Geological maps and the Alpine structure
Geologists create precise maps of rock outcrops to develop cross-sections through mountain belts, enabling a 3D view.
Reconstructing the geological scenario of Valais
Thanks to plate reconstruction and information gleaned from maps and cross-sections, a precise alpine scenario can be established.
Relics in the Val d'Hérens
The majority of sediments covering the Valais domain were detached and transported into the Fribourg, Vaud and Chablais Prealps.
Long, long ago in the Val d'Hérens
The sedimentary rocks deposited on the European continent cover an ancient basement that endured a deformation event older than the Alpine one, the Variscan Orogenic Event between 360 and 300 Ma. These basement rocks were formerly located on the Gondwana border within a mountain range.
How old are our mountains?
The formation of a mountain belt takes millions of years. The first mountains in the Alps appeared 30 Ma ago when a large part of the European crust was deeply subducted.
The Earth's climate
The cooling of the Earth’s climate started 30 Ma ago, but the northern hemisphere glaciations are primarily during the Quaternary Era (2.6 to 0 Ma). Several times the Alps were covered by a large, 2 to 3 km thick, ice cap.
Human Intervention
The first inhabitants in Valais during the Bronze Age exploited local copper ores. The Romans discovered new mines and mineral extraction continued up to the 20th century with the Comtesse Mine at Praz-Jean, containing lead, zinc and silver. Iron ore found near Lana also contributed to local tool building.
In the Val d’Hérens hot water springs exist in Combioula.
Where does this mineral wealth comes from?
There are numerous mineral ores in the mountain of Valais including the well-known Pierre ollaire originating from the transformation of peridotites from Earth’s mantle during the folding of the Alps.
Bibliography
GEOLOGICAL CROSS-SECTION
MAPS
VIDEO
SERVICES
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