Audio Series: ch.tours Thematic Guides Estimated Duration: 29 minutes Style: Engaging narrator voice for audio playback
Introduction
Welcome to ch.tours. I'm your narrator, and today we are going deep -- deep into the Earth, deep into time, and deep into one of the most extraordinary geological stories on the planet: the formation of the Swiss Alps. These mountains that define Switzerland, that shape its culture, its economy, its very identity, are not permanent fixtures. They are, in geological terms, young. They are still rising, still being sculpted, still changing. And their origin story involves colliding continents, vanished oceans, unimaginable pressures, and timescales that make human history seem like the blink of an eye. If you have ever looked at the Matterhorn and wondered how on Earth that shape came to be, this is your story. Let's begin about two hundred and fifty million years ago.
Segment 1: The Tethys Sea -- An Ocean Between Continents
To understand the Alps, you first need to understand that the world used to look completely different. About two hundred and fifty million years ago, during the late Permian period, all the world's continents were joined together in a single supercontinent called Pangaea. As Pangaea began to break apart, a vast ocean formed between the landmasses that would become Africa and Europe. This was the Tethys Sea -- named after the Greek sea goddess Tethys, wife of Oceanus.
The Tethys was a warm, shallow tropical ocean, teeming with life. Over tens of millions of years, the shells and skeletons of countless marine organisms accumulated on its floor, building up thick layers of limestone, mudstone, and other sedimentary rocks. These are the rocks that now form many of the peaks of the Swiss Alps. When you look at a limestone cliff face in the Bernese Oberland or the Jura Mountains, you are looking at the compressed remains of an ancient ocean floor.
This is one of the most astonishing facts about the Alps: the summit of many of the highest peaks is made of rock that was once at the bottom of the sea. Fossilised seashells, corals, and ammonites have been found at altitudes above four thousand metres. The ocean literally became the mountain.
Segment 2: The Great Collision -- Africa Meets Europe
About sixty-five million years ago -- roughly the same time as the asteroid that killed the dinosaurs -- the African tectonic plate began to move northward, slowly but relentlessly, toward the European plate. The Tethys Sea, caught between them, began to shrink. Over millions of years, the ocean floor was subducted -- pushed down beneath the advancing European plate -- and the sedimentary rocks that had accumulated on the sea floor were scraped off, compressed, folded, and thrust upward.
This is the fundamental mechanism of Alpine mountain building: collision. The African plate pushed into the European plate like a slow-motion car crash, and the Alps are the crumple zone. The collision is still happening. Africa continues to move northward at a rate of roughly two to three centimetres per year, and the Alps continue to rise -- though erosion wears them down almost as fast as they grow.
The process of mountain building, known as orogeny, was not a single event but a series of phases spanning tens of millions of years. Geologists distinguish several major phases: the Eo-Alpine phase, around ninety million years ago; the Mesoalpine phase, around forty-five million years ago; and the Neoalpine phase, which has been ongoing for the last thirty million years. Each phase involved different movements, different pressures, and different rocks being pushed to different positions.
Segment 3: Nappes -- The Folded Blankets of Rock
One of the most distinctive features of Alpine geology is the system of nappes. A nappe, from the French word for tablecloth, is a large sheet of rock that has been thrust over other rocks, sometimes travelling tens or even hundreds of kilometres from its original position. The Alps are essentially a stack of nappes, piled on top of each other like folded blankets.
This nappe structure was first recognised by Swiss geologists in the late nineteenth and early twentieth centuries, and it was a revolutionary insight. The great Swiss geologist Albert Heim, working in the late 1800s, was among the first to understand the enormous scale of Alpine folding and thrusting. His successor, Emile Argand, developed the nappe theory further, showing how entire sheets of rock had been peeled off the ocean floor and stacked up during the continental collision.
The implications are mind-bending. In the Alps, you regularly find older rocks sitting on top of younger rocks -- the reverse of the normal geological principle that younger layers lie above older ones. This is because the nappes have been flipped, folded, and thrust over one another. At the famous Glarus Thrust, visible in the canton of Glarus, a layer of rock roughly 250 to 300 million years old sits directly on top of rocks only 35 to 50 million years old. The thrust plane between them is so dramatic and so well exposed that it was designated a UNESCO World Heritage Site in 2008, as the Swiss Tectonic Arena Sardona.
Segment 4: The Matterhorn -- An African Summit in Europe
The Matterhorn, that iconic pyramid of rock rising to 4,478 metres above Zermatt, is perhaps the most famous mountain in the world. And its geological story is one of the most surprising. The summit of the Matterhorn is made of gneiss and other metamorphic rocks that originated not on the European continent but on the African plate.
Here is what happened: when Africa collided with Europe, a sheet of African crustal rock -- part of the so-called Dent Blanche nappe -- was thrust northward over the European basement rocks. The Matterhorn is the eroded remnant of this African nappe, sitting on top of European rocks. In geological terms, the top of the Matterhorn is a piece of Africa.
The mountain's distinctive pyramidal shape is the result of erosion by glaciers on all four sides. Each face of the pyramid corresponds to a different glacial cirque -- a bowl-shaped depression carved by ice. As the glaciers carved into the mountain from the north, south, east, and west, they left behind the sharp ridges and the pointed summit that we see today. This process, called horn formation, is a textbook example of glacial erosion, and the Matterhorn itself is the textbook illustration.
The first ascent of the Matterhorn, on July 14, 1865, by Edward Whymper and his party, was one of the most dramatic events in mountaineering history. Four of the seven climbers died during the descent when a rope broke. The tragedy and triumph of that day are inseparable from the mountain's mystique.
Segment 5: The Jungfrau Region -- A Geological Cross-Section
The Jungfrau-Aletsch region in the Bernese Oberland, a UNESCO World Heritage Site since 2001, is not only one of the most spectacular landscapes in the Alps but also one of the most geologically informative. The trio of peaks -- the Eiger (3,967 metres), the Monch (4,107 metres), and the Jungfrau (4,158 metres) -- expose a cross-section of Alpine geology visible from valley floor to summit.
The north face of the Eiger, that infamous 1,800-metre wall of rock, displays layers of limestone laid down in the Tethys Sea, now tilted nearly vertical by the forces of Alpine orogeny. The dark limestone bands alternate with lighter layers, creating the distinctive banded appearance visible from Grindelwald.
The Aletsch Glacier, at roughly twenty-two kilometres the longest glacier in the Alps, flows from the snowfields between the Jungfrau and the Monch down to an elevation of about 1,600 metres. It is a living demonstration of glacial processes: you can see crevasses, moraines, medial stripes of rock debris, and the glacier's snout retreating year by year as the climate warms. Since 1870, the Aletsch Glacier has retreated by roughly three kilometres and lost about half of its volume.
The Jungfraujoch, at 3,454 metres the highest railway station in Europe, offers visitors a chance to stand on the glacier and contemplate the forces -- tectonic, glacial, erosive -- that have shaped this landscape over hundreds of millions of years.
Segment 6: The Jura Mountains -- The Alps' Older Sibling
The Jura Mountains, which form Switzerland's northwestern border with France, tell a different geological story from the high Alps, though the two are intimately connected. The Jura are a fold mountain range, formed when sedimentary rocks -- primarily limestone laid down in warm Jurassic seas between about 200 and 145 million years ago -- were compressed and folded by the same tectonic forces that built the Alps.
The Jurassic period itself is named after the Jura Mountains, where these rocks were first studied and described by the French geologist Alexandre Brongniart in 1829. The fossils found in Jura limestones, particularly ammonites and belemnites, are among the best-preserved in Europe.
The Jura's geology differs from the Alps in being less violently deformed. While the Alps involve deep crustal rocks thrust up from great depths, the Jura are a more gentle affair: surface sedimentary layers buckled into a series of parallel ridges and valleys, like a crumpled rug. This "fold and thrust belt" structure produces the characteristic landscape of long, narrow ridges (called anticlines) separated by broad valleys (synclines) that give the Jura its distinctive topography.
The Jura are also notable for their karst landscapes -- terrain shaped by the dissolution of solite limestone by rainwater. Caves, sinkholes, underground rivers, and dramatic cliff gorges called cluses are common. The Creux du Van, a natural amphitheatre in the canton of Neuchatel with 160-metre vertical limestone cliffs, is one of the most impressive karst features in Switzerland.
Segment 7: Glaciers -- The Sculptors of the Landscape
If tectonic forces built the Alps, glaciers sculpted them. During the Pleistocene ice ages, which began roughly 2.6 million years ago and ended only about eleven thousand years ago, enormous ice sheets repeatedly advanced and retreated across the Alpine landscape. At their maximum extent, glaciers covered virtually the entire Swiss Plateau, reaching as far north as the Jura and as far south as the Po Plain in Italy.
These glaciers carved the landscape we see today. The characteristic U-shaped valleys of the Alps -- wide, flat-bottomed valleys with steep sides -- are the work of glacial erosion. The lakes of the Swiss Plateau -- Zurich, Lucerne, Thun, Brienz, Constance, Geneva -- are glacial in origin, occupying basins scooped out by advancing ice.
Moraines -- ridges of rock and debris deposited by glaciers -- dot the Swiss Plateau and the Alpine valleys. The gentle hills around Zurich are largely morainic, composed of material carried and dumped by the Linth Glacier during the last ice age. Erratic boulders -- rocks transported by glaciers far from their geological origin -- are found scattered across the plateau. The Pierre des Marmettes near Monthey in the Valais, a massive granite boulder perched improbably on limestone, was one of the key pieces of evidence that led the Swiss naturalist Louis Agassiz to develop his revolutionary ice age theory in the 1830s and 1840s.
Agassiz, born in Motier on the shore of Lake Morat in 1807, was the first scientist to propose that much of Europe had once been covered by vast ice sheets. His idea was initially ridiculed but eventually transformed our understanding of Earth's climate history.
Segment 8: The Gotthard Massif -- Switzerland's Geological Heart
The Gotthard massif, in central Switzerland, is the geological and geographical heart of the country. It is a dome of ancient crystalline rocks -- gneisses and granites over three hundred million years old -- that were pushed up to the surface during the Alpine orogeny. The Gotthard is where several of Switzerland's greatest rivers have their sources: the Rhine, the Rhone, the Reuss, and the Ticino all rise within a few kilometres of each other on the Gotthard.
This convergence of rivers made the Gotthard a place of immense strategic importance from the earliest times. The Gotthard Pass, at 2,106 metres, has been a major transalpine route since the thirteenth century. The Devil's Bridge, spanning the wild Schoellenen Gorge on the approach to the pass, was first built around 1230 and was considered such an engineering marvel that legend attributed its construction to the Devil himself.
The Gotthard's geology posed enormous challenges for tunnel builders. The original Gotthard Rail Tunnel, completed in 1882, was 15 kilometres long and took ten years to build, at the cost of nearly two hundred lives. Workers encountered extreme heat, unstable rock, and flooding. The Gotthard Base Tunnel, completed in 2016 at 57.1 kilometres, is the longest railway tunnel in the world. Its construction required boring through an extraordinary variety of rock types, from hard granite to soft, squeezing schist, and produced 28.2 million tonnes of excavated material.
Segment 9: Earthquakes and Active Geology
Switzerland is not an earthquake-free zone. The ongoing collision between Africa and Europe means that seismic activity is a real, if relatively moderate, hazard. The Swiss Seismological Service, based at ETH Zurich, records between 1,000 and 1,500 earthquakes per year in Switzerland, most too small to be felt.
But larger earthquakes do occur. The most destructive earthquake in Swiss history struck Basel on October 18, 1356. The Basel earthquake, estimated at a magnitude of 6.5 to 6.9, destroyed much of the city, killed hundreds of people, and was felt across a vast area from Paris to Prague. Fires raged for days in the ruins. It remains one of the most significant seismic events in central European history.
The Valais is Switzerland's most seismically active region today. A significant earthquake struck the town of Visp in 1855, reaching an estimated magnitude of 6.2 and causing widespread damage. Seismologists consider the probability of a similar event in the coming decades to be significant, and Switzerland has invested heavily in seismic monitoring, building codes, and disaster preparedness.
The country also experiences other geological hazards: landslides, rockfalls, debris flows, and avalanches are all part of life in a mountain environment. The catastrophic landslide at Goldau in 1806, when the Rossberg mountain collapsed and buried the village, killing 457 people, was one of the deadliest natural disasters in Swiss history. More recently, a massive rockfall from the Piz Cengalo in the Bregaglia valley in 2017, involving roughly three million cubic metres of rock, demonstrated that the Alps remain a dynamic and potentially dangerous landscape.
Segment 10: Water and Karst -- The Hidden Underground
Switzerland's geology creates a remarkable hydrological landscape both above and below ground. The country's abundant rainfall and snowmelt, combined with its complex geology, produce thousands of springs, waterfalls, and underground water systems.
The Trummelbach Falls, inside the Jungfrau massif, are the only glacial waterfalls in Europe accessible through a series of tunnels and lifts inside the mountain. Up to twenty thousand litres of water per second cascade through a spiral gorge carved through the rock, carrying away roughly twenty thousand tonnes of sediment per year from the glaciers above.
In the limestone regions of the Jura and the Pre-Alps, karst hydrology creates an underground world of caves and rivers. The Holloch cave system in the Muotathal valley of the canton of Schwyz is one of the longest cave systems in Europe, with over two hundred kilometres of explored passages. The caves at Vallorbe, in the Jura, feature an underground river and spectacular stalactite and stalagmite formations built up over hundreds of thousands of years.
Switzerland's thermal springs, found in places like Baden, Bad Ragaz, Leukerbad, and Lavey-les-Bains, are another geological gift. These springs originate as rainwater that percolates deep into the Earth through fractures in the rock, is heated by the Earth's internal heat, and then rises back to the surface. At Leukerbad in the Valais, the thermal water emerges at temperatures up to 51 degrees Celsius, and the town has been a spa destination since Roman times.
Segment 11: Climate Change and the Future of Alpine Geology
The geological processes that shaped the Alps operate on timescales of millions of years, but the more recent sculptors of the landscape -- glaciers and weathering -- are responding to climate change on timescales of decades. Switzerland's glaciers are retreating at an accelerating rate. Between 2001 and 2022, Swiss glaciers lost roughly a third of their remaining ice volume. The summer of 2022 was particularly devastating, with record ice loss.
The retreat of glaciers has multiple geological consequences. New lakes are forming in the basins left behind by retreating ice. Slopes that were stabilised by permafrost -- permanently frozen ground -- are thawing, increasing the risk of rockfalls and landslides. The Piz Cengalo rockfall of 2017 is thought to have been at least partly related to permafrost degradation.
Glacier retreat also affects water resources. Swiss glaciers act as natural reservoirs, storing water as ice in winter and releasing it as meltwater in summer. As glaciers shrink, this buffering effect diminishes, potentially leading to reduced summer river flows and impacts on hydroelectric power generation, agriculture, and drinking water supply.
Scientists at institutions like ETH Zurich, the University of Bern, and the Swiss Federal Institute for Forest, Snow and Landscape Research (WSL) are actively studying these changes. Their work is crucial not only for understanding the future of the Alps but for understanding the global implications of climate change in mountain environments.
Segment 12: Closing Narration
The next time you stand before an Alpine panorama -- perhaps at the Jungfraujoch, or on the shores of Lake Lucerne, or gazing up at the Matterhorn from Zermatt -- remember what you are looking at. You are looking at the result of two hundred and fifty million years of geological drama: oceans opening and closing, continents colliding, rocks being squeezed, folded, and thrust skyward, glaciers advancing and retreating, rivers cutting gorges, and gravity pulling mountains slowly, relentlessly back down.
The Alps are not static. They are a work in progress, shaped by forces both ancient and ongoing. The ground beneath your feet was once an ocean floor. The summit above your head may be a piece of Africa. The valley you stand in was carved by ice a mile thick. And the whole magnificent landscape is still moving, still changing, still alive in the deepest geological sense.
Thank you for joining me on this journey into deep time. I'm your narrator from ch.tours. Look at these mountains with new eyes, and safe travels.
This audio script is part of the ch.tours thematic audio series. For more guided experiences across Switzerland, visit ch.tours.