Glossar

 

Geology of Switzerland

The underground environment of Switzerland is highly diverse.

In Switzerland, it is possible to find a rich variety of rock types and landscape features over a relatively small area.

During the geological history of the Earth, the area that is now Switzerland was covered several times by an ancient sea. Evidence of this exists in the form of the thick limestone layers in the Jura region and the Helvetic Zone.

During the formation of the Alps, rock material removed by erosion was deposited as molasse in the Swiss Plateau in front of the rising mountain chain.

Switzerland can be divided from north to south into four distinct units.

(Source: swisstopo)

Folded and Tabular Jura
Molasse – Plateau
Helvetic Zone – Northern Alps
Crystalline – Central and Southern Alps

 

Folded and Tabular Jura

The Swiss Jura Mountains comprise the Folded Jura and the Tabular Jura that form the western and northern margins of Switzerland. The mountains consist mainly of limestone, marl and clay, as well as anhydrite/gypsum.

Around 15 to 10 million years ago, the pressure from the formation of the Alps affected the area of Northern Switzerland. This pressure folded the rocks in the region, resulting in the Folded Jura.

The Creux du Van (Canton Neuchatel) is an example of thick limestone deposits from the Jurassic period some 160 million years ago. The immense rock arena was formed by folding and erosion and is one of the most impressive places in the Jura. Image: Nagra

 

Molasse – Plateau

The Molasse Basin extends from Lake Constance to Lake Geneva. Over the last 30 million years, Large amounts of eroded material accumulated in the foreland basin to the north of the uplifting Alps. The subsurface consists of sandstone, silt and marl as well as Nagelfluh (conglomerate).

A distinction is made between marine and freshwater molasse, depending on whether the sediments were deposited in the sea or in lakes and river valleys.

These deposits are overlain by unconsolidated rocks from the ice ages that were transported to their location by glaciers.

Landscape in the Zürcher Weinland region looking over the Molasse Basin towards the Alps on the horizon. Image: Nagra

Helvetic Zone – Northern Alps

From a Swiss perspective, the Alps can be divided into the Northern, Central and Southern Alps. There are further sub-divisions for the alpine range as a whole. The so-called Helvetic Zone forms the northern margin of the Alps from Lake Thun to the Rhine valley. It consists of limy and marlly sediments that were deposited in an ancient shallow sea in the period from 250 to 65 million years ago.

«So kam der Fisch auf den Berg - Dokumentation von NZZ Format (2005)», Film zur Entstehung der Alpen. Quelle: YouTube, NZZ Format

Whole mountains shifted to the north

The pressure during the orogeny deformed the rocks in the area of the alpine belt. Today, many of the sediments from the ancient Tethys sea are no longer at the location where they were deposited as they were sheared off, folded and transported several kilometres to the north. This can be seen in the case of the Helvetic sediments: during a late phase of the alpine orogeny, these sediments were sheared off from the crystalline bedrock due to pressure from the African continental plate advancing from the south. They were thrust over the existing rock mass up to a distance of 50 kilometres to the north-west where they form thick stacks of nappes today. The soft layers of marl and clay shale contained in these rock packages served as a lubricating material. Helvetic nappes are found, for example, at Säntis, Titlis and Churfirsten.

The Churfirsten is an imposing example of the nappes of the Helvetic Zone. Image: © swisseduc / Dr. Jürg Alean

Crystalline – Central and Southern Alps

The Swiss Alps form the central part of the entire alpine belt, which extends from Nice on the Mediterranean to Vienna. The high peaks and glaciers are characteristic of the Central Alps, which are made up of sedimentary, crystalline and metamorphic rocks. Many of the summits are still pointed and sharp-edged as they were neither covered by ice nor eroded by it during the ice ages. 

«Gebirgsbildung & Plattengrenzen einfach erklärt – Wie entstehen Gebirge?», Quelle: YouTube, Die Merkhilfe

Africa and Europe collide

From a geological point of view, the African and Eurasian plates collide in the Alps. The African plate has been moving northwards over the last 130 million years and is pushing against the Eurasian continent. The alpine orogeny began around 80 million years ago at the end of the Cretaceous, as a result of the incipient collision of the African and Eurasian plates. This reached a peak some 30 million years ago. Due to the thrust from the south and the constriction of the rock masses, they not only moved upwards but also downwards. The thickness of the continental crust increased to well over 50 kilometres.

Alps are like a floating iceberg

The Alps consist mainly of continental crust, which has a lower density than the underlying part of the earth's mantle. Due to the thickening during the formation of the Alps, the crust is thicker in the Alpine region than in the foreland. The situation can be compared to an iceberg floating in water. Ice has a lower density than water. When the iceberg melts at the top, it rises out of the water until equilibrium is restored.

Erosion leads to uplift of the Alps

There is also a loss of mass in the Alps. Weathering and erosion are responsible for this. Even when the formation of the Alps began, material was being removed by processes involving gravity, flowing water or wind. This material was deposited in the Plateau as Molasse. This sediment redistribution was intensified particularly during various glaciations in recent times.

Earthquakes due to alpine uplift

The area around Brig and Chur is uplifted by up to 1.5 millimetres per year. Earthquakes are also more frequent in these areas. The continuous uplift and deformation and the associated erosion are an important reason why the Alpine region is not suitable for a repository for radioactive waste.

Sidelhorn

Granite landscape in Central Switzerland. The dome in the centre of the picture was rounded by the action of glacier ice, while the peaks in the background have retained their sharp edges. Image: Nagra

Central massifs with crystalline bedrock

While the crystalline basement lies hidden beneath the Molasse fill and marine sediments in the Plateau, in the Central Alps it is visible at the surface. The central massifs such as the Aar, Gotthard and Mont Blanc massifs in the southwest of our country consist mainly of granitic rocks and gneisses. The pressure during the formation of the mountains strongly deformed the rocks in the area of the Alpine belt. Both the Aar and Gotthard massifs were compressed but not moved away from their place of origin. These massifs are surrounded by sediments that have been metamorphically overprinted in various ways.

At the Grimsel Test Site, Nagra is carrying out research into radioactive waste disposal. The Test Site is located in granitic rocks of the Aar Massif and can be visited by appointment.

Marked fault zone through Canton Ticino

Further south in CantonTicino lie first the Penninic crystalline nappes and then the "Insubric line". The Adriatic Plate meets the European Plate at this marked fault zone, which runs from east to west through the Alps. South of this line lie the Southern Alps, which consist of crystalline on the one hand and sediments in the area south of Lugano on the other. The central Alps with Penninic nappesand a large part of the southern Alps therefore consist of crystalline.

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