Glossar

 

Geology of Switzerland

Switzerland has interesting geology to offer

In Switzerland, it is possible to find a wide variety of landscape features over a relatively small area – from the Alpine range through the Plateau to the Jura Mountains. Here you will find important information on evolutionary history, geology and the characteristic rock formations of the different landscapes. Did you know that parts of Switzerland were covered several times by an ancient sea? Visit one of the two Swiss rock laboratories and experience how Opalinus Clay or granite were formed. Experience "live" what it looks like underground.

Geological history of Switzerland

Marine deposits, the folding of the Alps and the Jura Mountains, rock erosion and glaciation have all shaped how Switzerland looks today. The map shows the geological conditions and the distribution of rocks at the earth’s surface.

Geologische Karte der Schweiz

Geological map of Switzerland. Source: swisstopo

Switzerland can be divided from north to south into four distinct units. These can be seen clearly on the simplified map:

  • Folded and Tabular Jura in the north and north-west, consisting of limestones, clays and anhydrite/gypsum
  • Plateau with the Molasse Basin filled with sandstones, Nagelfluh, silt and marls
  • Northern Alps with the Helvetic Zone, consisting mainly of marls and limestones
  • Central and Southern Alps with crystalline rock, consisting mainly of granites and gneisses

Vereinfachte geologische Karte der Schweiz mit Profillinie

Simplified geological map of Switzerland with profile line (see figure below). Source: NagraGeologisches Profil der Schweiz von Nordnordwesten nach Südsüdosten

Geological profile of Switzerland from north-northwest to south-southeast (see text for numbers). Source: Nagra NTB 14-02, Dossier III (highly simplified)

Troughs form in the bedrock

Crystalline plutonic, metamorphic and dyke rocks [1] formed in the earth's crust. More than 250 million years ago, troughs [2] were formed in the crystalline bedrock during the Permian and Carboniferous periods. These were then filled with debris eroded from the surrounding mountains. The remains of such a Permo-Carboniferous trough can be found beneath northern Switzerland between Frick and Constance.

Jurassic sea covers Switzerland

During the Jurassic period, Switzerland was mostly covered by an ancient sea. Sediments were deposited on the ocean floor, which today lie as rock formations [3] on top of the older basement. In the Late Cretaceous and the Tertiary, collision of the Adriatic and Eurasian tectonic plates led to the formation of the Alps. During a relatively late phase of the alpine orogeny, the rocks of the Helvetic deposition zone were broken into rock stacks, folded and transported northwards [4]. Between the stacks lies the eroded material still being deposited in the sea from the forming Alps [Flysch 5]. Further eroded material from the uplifting Alps, so-called Molasse, accumulated in the Molasse Basin [7] in the foothills of the Alps.

Alpine orogeny leads to Jura folding

The pressure from the forming Alps extended into Northern Switzerland. This pressure caused the sedimentary rocks to shear off from the crystalline basement and fold to form the Folded Jura [6].

Excerpt from the geological timescale
(in millions of years)

Carboniferous: -358.9 to -298.9
Permian: -298.9 to -252.2
Triassic: -252.2 to -201.3
Jurassic: -201.3 to -145
Cretaceous: -145 to -66
Tertiary (Palaeogene & Neogene): -66 to -2.588
Quaternary: -2.588 to 0

Folded and Tabular Jura

The Folded Jura and Tabular Jura consist mainly of limestone, marl and clay, as well as anhydrite/gypsum. The Tabular Jura extending from north-west Switzerland to the Schaffhausen region is a so-called cuesta landscape formed by the differing erodibility of the rock types. Predominantly in north-west Switzerland, the strata are divided into blocks by north-south running fault zones. This typical surface structure of the Tabular Jura with higher areas and valleys, known as fault block mountains, formed with the development of the Rhine Graben in the Cenozoic around 40 million years ago.

The Folded Jura describes an arc extending from the region of Geneva and neighbouring France in the west to Baden in the east. In the Folded Jura, sedimentary rocks were compressed and folded due to the alpine orogeny. The thick limestone deposits can be clearly seen, for example, at Creux du Van (NE). The Folded Jura is penetrated in only a few places by narrow transverse valleys. Roads often lead through these gorges; otherwise road connections require a tunnel or a mountain pass.

Immense rock arena of Malm limestone formed by folding and erosion. "Creux du Van | Travelling Switzerland. A view you don't want to miss!", source: YouTube, TheMegaMatt

Experience the Folded Jura underground

Tunnels through folded formations in the Jura offer easy access to rock layers that often lie at depths of several hundred metres in the Plateau. This is true of the Opalinus Clay in particular. As a host rock, it will one day safely contain the radioactive waste in a deep geological repository at a site to be determined. Research on the Opalinus Clay is being carried out in the Mont Terri Rock Laboratory at St-Ursanne. The access to the rock laboratory is via the security gallery of the Mont Terri motorway tunnel. The impermeable Opalinus Clay is reached after only a short journey through permeable limestone layers. The Opalinus Clay sediments formed in the Jurassic sea are rich in fossils such as ammonites.

The rock laboratory can be visited free of charge by appointment. You can find more details here and register for a guided tour.

A journey through the Mont Terri Rock Laboratory. "Tunnel Flight", source: YouTube, swisstopo

Molasse – Plateau

The Plateau lies between the Jura Mountains in the north and the Alps in the south and extends from Lake Constance to Lake Geneva. It is characterised by marked river courses and lakes.

Video in German about the Swiss Plateau and its sediments. "Geologie Schweiz – Mittelland im Tertiär: Molassebecken", source: YouTube, Thomas Cinar

Video on the formation and erosion of the Alps resulting in a molasse-filled foreland basin. "Growth and erosion of an orogenic wedge (re-upload)", source: YouTube, TheGeoModels

Molasse Basin with rock debris from the Alps

Deep beneath the Swiss Plateau lies the crystalline basement. This is covered by sedimentary sequences from the Mesozoic (particularly marine sediments such as limestones and clays). Above this lies the so-called Molasse, erosion debris from the forming Alps. In the final phase of the alpine orogeny, the earth's crust subsided under the weight of the mountains and a depression formed in the foothills of the Alps. This was continuously filled with debris (gravel, sand, silt and clays), which was transported by rivers from the Alps to the north over a timespan of around 30 million years – the Molasse Basin was formed.

"Weathering And Sedimentation", source: YouTube, Earth Rocks!

"Weathering and Erosion", source: YouTube, Studies Weekly

Marine and Freshwater Molasse contain fossils

Erosional debris from the Alps was deposited in the sea or in lakes and river valleys, hence the distinction between Marine and Freshwater Molasse. Deposition was according to grain size: finer particles such as clay platelets were transported far into the sea, up to the edge of the present-day Jura. Coarser particles could not remain suspended for so long in the rivers and therefore remained in rivers closer to the Alps, for example as gravel beds. The Marine Molasse is fine-grained and consists of marl, sandstone, silt and clay. The Freshwater Molasse contains a larger coarse-grained component such as Nagelfluh (conglomerate) and sandstone. Different layers are rich in fossils: Freshwater Molasse contains leaves, freshwater snails and mussels; the Marine Molasse contains sea snails and mussels as well as sharks' teeth.

Rivers and streams transport rock material over large distances. Mudslide in Illgraben (Leuk, VS). Following a heavy thunderstorm, the mountain stream carried large amounts of boulders, rock debris and mud. "Illgraben 28 juillet 2014, front de lave", source: YouTube, PiperLambert

Lower Marine Molasse is formed

Seawater penetrated into the depression formed in the Plateau in the final phase of the alpine orogeny. Sediments such as marls and sandstones deposited in the depression around 35 to 30 million years ago belong to the Lower Marine Molasse.

Lower Freshwater Molasse is formed

Around 30 million years ago, large volumes of erosional debris were transported to the Molasse Basin as a result of the strong uplifting of the Alps, and the sea quickly silted up. The sediments that were then deposited some 30 to 20 million years ago mainly in rivers belong to the Lower Freshwater Molasse. The coarse-grained components were deposited as Nagelfluh (conglomerate). In a later phase of the alpine folding, the Molasse rocks deposited near the Alps were compressed, displaced and lifted out of the Molasse Basin (e.g. formation of Rigi).

Upper Marine Molasse

As the sea-level rose, the Plateau was again flooded by the sea some 20 million years ago. The sediments of the Upper Marine Molasse such as sandstone and marl were deposited in the narrow, shallow sea between around 20 and 18 million years ago. Deltas and alluvial fans formed at the same time.

Upper Freshwater Molasse

18 to 14 million years ago, the sea retreated once again. In the Plateau there were numerous lakes and rivers, large alluvial fans at Hörnli and Napf filled with gravel, and extensive flood plains with sand, silt and mud. These sediments of the Upper Freshwater Molasse solidified to form conglomerates such as Nagelfluh, sandstones and marls.

Landschaft im Zürcher Weinland mit Blick über das Molassebecken bis zu den Alpen am Horizont

Landscape in the Zürcher Weinland with a view over the Molasse Basin towards the Alps on the horizon. Image: Nagra

The Plateau is affected by an ice age

Above the Molasse lie unconsolidated rocks (e.g. gravel, scree, sand, silt, clay) from the ice ages of the last two million years; these were transported by rivers and glaciers. Glaciers and meltwater have a large erosive power and have significantly shaped today's Plateau topography. This is evidenced by the numerous extended lakes running from south-southeast to north-northwest on the edge of the Alps, whose rock beds lie mostly under thick unconsolidated rocks. These glacial rocks are not consolidated and therefore present difficult construction ground, but also provide raw materials in the form of gravel and drinking-water supplies. From time to time mammoth teeth are also found.

Advance and retreat of the Alpine glaciers during the last glacial cycle from Julien Seguinot on Vimeo (licence: CC BY-SA 4.0).

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. Its sediments consist of lime and marl that were deposited in an ancient shallow sea in the period from 250 to 65 million years ago.

Video on the formation of the Alps. "Assembly of the Alps", source: YouTube, GeologVlog

Whole mountains shifted to the north

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

 

Video on sediments that have been thrusted over the existing rock mass. "Lesson 10: The Alps & Geology", source: YouTube, D.J. Lake

Die Churfirsten sind ein eindrückliches Beispiel für die Deckenstapel des Helvetikums.

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 (more information on these rocks and the rock cycle: link). 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.

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.

Clickable screenshot from YouTube video "Switzerland Alps understanding mountains landscape geology" from 4scienceprod production

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. The higher-lying peaks in the background were not covered by ice and have thus 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.

Video on the Crystal Cavern next to the Grimsel Test Site. "Amazing Crystal Cavern in Switzerland", source: YouTube, SpaceBalloon Fr

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. You can register here.

Marked fault zone through Canton Ticino

Further south in Canton Ticino 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 nappes and a large part of the southern Alps therefore consist of crystalline.

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