How mountains were formed by tectonic plates

Mountains in motion

Mountains rise up mighty and rigid. It seems as if nothing and no one can move them from the spot. But that's not true: mountains are constantly in motion - albeit so slowly that we cannot see the change with the naked eye.

The reason for this: the plates of the earth's crust move. And when two of these plates collide, the rock is compressed, pushed and piled up. Similar to a car accident, mountains fold up on the edge of the slab on impact. Mountains and valleys are therefore a “crumple zone” of the slabs colliding. However, this does not happen suddenly like in a car accident, but much more slowly than in slow motion. The result is fold mountains like the Andes in South America. There the oceanic Nazca plate slides under the South American plate and squeezes the rock with incredible force. The elongated mountains of the Andes piles up, stretching over a distance of 7,500 kilometers. The Andes are the longest unearthly mountain range in the world.

However, there are also huge mountains below sea level. They pull themselves through the middle of the oceans. They too owe their existence to the movable plates. Where two plates move away from each other on the ocean floor, magma penetrates from the mantle through the oceanic crust. The hot rock slurry cools on the sea floor and piles up to form mountains that are thousands of meters long: the mid-ocean ridges. Where the lava reaches sea level and swells beyond it, islands like Iceland arise. These mountains, which are born in the sea, are the longest on earth. The Mid-Atlantic Ridge stretches from north to south through the entire Atlantic - about 20,000 kilometers long.

29.5.1953

They dreamed of it for years, they climbed for weeks: On May 29, 1953 at 11.30 a.m., New Zealander Edmund Hillary and Sherpa Tenzing Norgay reached their ambitious goal: They were the very first to climb Mount Everest!

Since the beginning of May, a British expedition has been preparing to climb the highest mountain on earth. A dozen experienced mountaineers, 35 mountain guides and 350 porters with 18 tons of equipment have been on their way from Kathmandu to the foot of Everest since spring. A first attack on the summit takes place on May 26th. But the climbers Tom Bourdillon and Charles Evans fail because of a defective oxygen device: Shortly before the finish line, the two have to turn back.

This is the moment for Edmund Hillary and Tenzing Norgay, who are waiting for their chance at base camp. As the second team, they begin the dangerous ascent. On May 28, they spend an icy night at an altitude of 8,500 meters. The next morning at 4 a.m. they start their last stage: 350 meters in altitude and a vertical rock step are still ahead of them - hardly manageable at this height. But at 11.30 a.m. the two actually made it: They are standing on the highest point on earth, the world is at their feet! Tenzing throws his arms around Hillary. The New Zealander pulls out his camera to capture the situation: the “third pole” has been reached! After 15 minutes on the summit, the two heroes set out on the dangerous descent.

For a long time, the 8,848-meter-high Mount Everest was considered invincible. Many expeditions had failed because of the notorious giant in the Himalayas in the past few decades. Brits George Mallory and Andrew Irvine might even have made it before Hillary and Tenzing. However, they perished during the descent and remained missing. To this day nobody knows whether they actually stood on the "mountain of mountains".

The storm night before the summit storm

Before Edmund Hillary and Tenzing Norgay reached the summit of Everest, they spent a terrible, icy night. Hillary described her incredible hardships as follows:

“The night was terrible. An icy storm swept over the highest peak on earth. Tenzing called it the roar of a thousand tigers. The storm swept relentlessly and relentlessly, howling and screeching, overhead, with such force that the canvas of our pyramid tent crackled like gunfire. We were on the south saddle, a godforsaken place between the peaks of Everest and Lhotse. Instead of lying down, the storm was still picking up the force, and I was beginning to fear that our fluttering and creaking shelter might be torn from its anchorages and exposed to the elements without protection. In order to save weight, we had left the liners of our sleeping bags behind, which now turned out to be a serious mistake. Even though I was wearing all of my down clothing, the freezing cold got to my bones. A feeling of extreme fear and loneliness came over me. What was the point of it all? You had to be crazy to do something like that to yourself! "

After surviving the stormy night, the summit storm was imminent: “We had no time to lose. I hit the stairs again and began to look for the summit, a little worried. It seemed to go on forever, and we were tired and moving more slowly. In the distance the barren plateau of Tibet spread out. I looked up to the right and saw a snowy bulge. That had to be the summit! We moved closer together as Tenzing tightened the rope between us. Again I hit a step in the ice. And in the next instant I was on a snow surface with nothing but air - in every direction. Tenzing quickly followed me and we looked around in amazement. We found with tremendous satisfaction that we were at the highest point on earth. It was 11.30 a.m. on May 29, 1953. "

26.6.2009

Drei Zinnen, Rosengarten and Geislerspitzen - the steep rock groups of the Dolomites rise mightily over the otherwise gently undulating landscape. Because of their "unique monumental beauty", the Dolomites have now been added to the UNESCO World Heritage List.

Its peaks protrude into the sky like sharp teeth. Anyone visiting the Dolomites is walking across ancient coral reefs and scrambling across the history of the earth. Like the entire Alps, the Dolomites began to rise and unfold from the sea floor millions of years ago. Over time, wind and weather formed gentle slopes at the foot of their peaks. Today cows graze here in summer.

Thousands of tourists come every year to marvel at the fabulous landscape. Extreme climbers perform circus-ready tricks on the steep walls. The fairytale-like setting attracts not only hikers and mountaineers, but also celebrities: Hollywood stars like George Clooney and Tom Cruise have already stayed here. And Reinhold Messner, himself born in Bressanone, began his career as an extreme climber on the walls of the Dolomites.

The World Heritage Committee was also impressed by the grandiose nature: On June 26th, parts of the Dolomites were declared a World Heritage Site by UNESCO. The Dolomites are now under special protection.

How the “pale mountains” became the Dolomites

The Dolomites are also called “pale mountains” because of their color. The Ladins, the oldest inhabitants of the area, tell each other many stories about their mysterious mountains: There is talk of the dwarf king Laurin and his enchanted rose garden and of a dwarf people who have woven the peaks with threads of moonlight. This mountainous landscape has always stimulated the imagination.

The French geologist Déodat de Dolomieu, on the other hand, took a more sober look at her light-colored rock. Upon closer inspection, he found that they were not made of pure limestone, as suspected. The salt magnesium oxide also had a large share. The newly discovered rock of the mountain range was named after its discoverer, Dolomieu: the dolomite. And the “pale mountains” turned - simsalabim - into the Dolomites.

17.11.1963

30 kilometers south of Iceland, an island was born out of the sea. A young volcano has been spewing fire and ashes here since November 14th. Its lava masses have already given rise to an island 40 meters high and 500 meters long.

White-gray ash clouds hang in the sky and darken it. Fine volcanic rock patters the area, every lava discharge is accompanied by the rumble of thunder. The smoke column caused by the volcanic eruption rises 10 kilometers. And an island off Iceland's south coast continues to grow.

The eruption of the underwater volcano came unexpectedly, but not without its harbingers. Seismologists had already measured smaller earthquakes a week earlier in the capital Reykjavik - signs that a lot is happening at the plate boundary of the Mid-Atlantic Ridge. In addition, a research ship had found that the sea was warmer than usual. And residents of the nearby coastal region believed they smelled hydrogen sulfide. When the volcano erupted on the seabed at a depth of 130 meters, it initially went unnoticed. Its explosions were weakened by the water pressure. But as it grew, it approached sea level and finally broke through it, spitting wildly. That was the birth of an island in Iceland.

The new island off the south coast already has a name: "Surtsey" it is called after Surt, the giant of fire. A Nordic legend tells of him that he hurls fire and destroys all life with his glowing sword.

How Iceland came into being

Iceland is actually nothing more than the climax of a huge mountain range in the Atlantic: The mid-Atlantic ridge, which stretches from north to south through the entire Atlantic, is almost 20,000 kilometers long. At the level of Iceland, the North American and Eurasian plates drift apart, by about two centimeters every year. Where they spread, hot magma penetrates from the interior of the earth to the surface. These volcanic eruptions have been piling up mountains underwater for millions of years and caused Iceland to appear above sea level 17 to 20 million years ago. These volcanoes are still active today. And now they have born another island: Surtsey.

Continents on the move

For a long time it was thought that the land masses of the earth would stand rigidly in place. It later turned out that the opposite is the case. The continents of our planet are moving! Like huge ice floes, they drift in different directions, albeit not very quickly. Their speed corresponds roughly to the growth of a fingernail. But why is it that the continents are constantly on the move?

The earth's crust that envelops our planet is brittle and cracked. It resembles a cracked egg shell and is made up of seven large and many smaller plates. Some of them make up the continents, others make up the ocean floor. These plates of the earth's crust float around on a hot, viscous rock slurry and are driven by movements in the earth's interior, more precisely: by currents in the earth's mantle. Experts also say: you are drifting. All of these processes related to the movement of the earth's plates are called plate tectonics, and the movement itself is also known as plate drift.

The earth is particularly active where the individual plates adjoin one another. At some of these plate boundaries, hot rock penetrates upwards from the earth's mantle and cools down. Here new earth crust forms: the two plates grow and are thereby pushed apart. On the other hand, where two plates collide, the lighter one of them - the continental crust - is crumpled up and unfolded to form mountains. The heavier of the two - the oceanic crust - is slowly disappearing into the depths. Due to the heat in the earth's interior, their rock is melted again. As the edge of the plate sinks into the depth, it pulls the rest of the plate behind it and thus additionally drives the plate movement.

Volcanic eruptions, earthquakes, long mountain ranges and deep ocean trenches accumulate along such plate edges. Most of the unrest on the earth's surface brings with it the largest of its plates: it is the Pacific plate, which is moving northwest at a rate of about 10 centimeters per year. Most of the world's active volcanoes can be found at their edges, and violent earthquakes shake the region. Because of the frequent volcanic eruptions and earthquakes, this plate boundary is also called the “Pacific Ring of Fire”.

Where plates collide

When two vehicles collide, their sheet metal is crumpled together. Something similar happens when two plates of the earth's crust collide. Then their rock is pushed together and very slowly laid into huge folds - this is how fold mountains arise. What the crumple zone is in a car accident, the mountains are in a collision of plates - only that a car accident takes place in fractions of a second, whereas a plate collision takes many millions of years.

This is exactly how the Alps came into being: Africa pressed against the Eurasian continent and unfolded the mountains. The Himalayas in Asia and the Andes in South America also owe their origins to the collision of migrating crustal plates.

In such a crash, the rock of the lighter plate is pushed upwards, the heavier plate sinks into the depths. This process is called subduction, the area in which the plate descends, the subduction zone. There are often deep gullies along these zones, which is why they are easy to see. The deepest of them is the Mariana Trench in the Pacific Ocean. This deep-sea channel lies where the Pacific plate dips under the Philippine one.

The further the earth's crustal plate disappears, the hotter it gets. The rock melts and magma forms in the depths. Due to the increasing pressure, it can be pressed up again. Where it penetrates to the surface of the earth, volcanoes spew lava and ash. There are entire chains of such volcanoes around the Pacific Plate, for example in Indonesia. Because one volcano follows the other, this plate boundary is also called the “Pacific Ring of Fire”.

Not only do volcanoes erupt at such plate edges. The earth also frequently trembles because the movement of the plates creates tremendous pressure and increasing tensions. As soon as these discharge, quakes shake the earth's surface. In Japan, for example, three plates meet: the Pacific, the Filipino and the Eurasian. It is for this reason that violent earthquakes hit Japan so often.

Where plates diverge

A long, deep crack gapes in the earth and is getting wider and wider. Huge forces are tearing the earth's surface to pieces: the East African Rift runs along this break through the continent. Africa began to break up here 20 million years ago. Hot magma from the earth's interior pushed up and tore the earth's crust apart. Since then, the pieces of crust have drifted apart, by about an inch every year. The fact that the earth is very active here can also be seen from the many volcanoes that rise along the rift. Should seawater ever penetrate, the East African Rift will become an ocean. Something similar happened in the Red Sea. The African and Asian continental plates have been separating there for 25 million years. The resulting crack was flooded by sea water.

There where continental Crust breaks apart, one arises Rift valley. Where against it oceanic When pieces of crust move away from each other, mountains grow on the sea floor: the Mid-ocean ridges. They consist of magma that seeps up from the Earth's mantle through the oceanic crust. New sheet material is formed here. It presses itself, so to speak, between two oceanic plates and solidifies to form basalt rock that piles up further and further.

In some places the mid-ocean ridges protrude as islands above sea level. Iceland, for example, and the still young Icelandic island of Surtsey are nothing more than parts of the Mid-Atlantic Ridge. The oceanic crust is constantly growing here due to the replenishment of solidified rock. It not only grows in height, but also to the sides. The two oceanic plates are pushed outwards. Because they spread apart in the process, one also speaks of one Divergence zone.

In this way, new seabed is created and the ocean is slowly getting wider - but only a few centimeters a year. But modern satellites can measure the continents with millimeter precision. From the movement one can calculate that the Atlantic has already been 25 meters wider since Columbus' crossing in 1492.

But because the earth as a whole is not getting any bigger, the increase in the seabed has to be compensated for elsewhere. This happens where the oceanic crust is submerged under the continental crust: While the Atlantic continues to grow, the Pacific slowly sinks under the plate margins of America and East Asia.

A constant race: uplift versus erosion

The Matterhorn or Mont Blanc would actually be over 12,000 meters high today - if wind and weather hadn't constantly attacked them. Because while the mountains are raised by forces in the earth's interior, they also shrink again at the same time: their rock is washed out and sanded off by water, wind and frost. In the case of the Alps, uplift and erosion are currently in balance. They stay about the same height.

Unlike the Alps, the Himalayas grow about one centimeter in height every year. In this region, the Indian plate presses against the Eurasian plate and raises the Himalayas further - so much that the erosion cannot keep up.

But there are also mountains where the unfolding has come to an end - they only shrink. These mountains were formed over 300 million years ago, so they are much older than the Alps or the Himalayas. Many of our low mountain ranges belong to them, for example the Rhenish Slate Mountains or the Bavarian Forest. They were abraded over millions of years and are now lower than 2000 meters.

The "race" between growth and shrinkage can also be observed in volcanic mountains: extinct volcanoes are constantly losing height. The Kaiserstuhl on the eastern bank of the Rhine, for example, is badly weathered. Today only ruins are left of the former volcano. Etna in Sicily, Europe's most active volcano, on the other hand, can suddenly grow a few meters in the event of an eruption. However, it occasionally loses height again when the cold lava collapses.

Folded and reshaped - the creation of the Alps

Every year Munich and Venice come half a centimeter closer. It's not a lot, but it's measurable. The fact that the German and Italian cities are slowly moving closer together has to do with the formation of the Alps.

Compared to other mountains, the Alps are relatively young. Its story begins “only” around 250 million years ago when a shallow sea formed between the continents of Eurasia and Africa: the Tethys. Rock debris and remains of living things settle on the sea floor over a long period of time and turn into limestone.

About 100 million years ago, the African plate set out on a journey: It drifts north, pressing violently against the Eurasian continent. The rock is compressed by the pressure, it folds up in a wave-like manner. The individual folds can reach a few millimeters or hundreds of meters. In some places the folded layers slide over one another like roof tiles and form what are known as rock ceilings. Eventually magma also rises; at the moment when the African plate dips under the Eurasian plate. The rock is melted in the interior of the earth and rises upwards, but still cools below the surface of the earth. For this reason, the central Alps consist of the igneous rock granite - in contrast to the limestone of the northern and southern Alps.

The folded area eventually rises above sea level under the great pressure. At first, the folds appear as elongated islands in the sea. But the archipelago is pressed further upwards and slowly pushes up to a high mountain range in which the rivers cut deep valleys. Large amounts of rubble are piled up in the foothills of the Alps. During the cold periods, huge glaciers carve deep trough valleys and steep mountain slopes into the rock. Only now is the typical high mountain landscape of the Alps forming, which attracts us to hiking or climbing in summer and skiing in winter.

The African plate continues to drift north to this day. That is why the Alps are still being lifted and compressed. This compression is the reason that Venice and the entire area beyond the Alps move a tiny bit closer to us every year.

How do mussels and corals get to the Alps?

The Zugspitze, Germany's highest mountain, is nothing more than a petrified reef. Whoever climbs it hikes over ancient coral remnants. Fossils such as fossilized giant clams and ammonites can be found on the Dachstein in Austria or in the Dolomites. But how did these remnants of marine animals get to the highest peaks in the Alps?

Today's Alps have lifted themselves out of a shallow sea, the Tethys Sea. About 200 million years ago this sea penetrated north and covered parts of southern Germany. At that time there was a tropical climate here, it was much warmer than it is now. Today the area would probably be a vacation paradise like the Maldives. At that time, however, no people lived here. Instead, in addition to ichthyosaurs, there were also mussels, ammonites and corals in the warm sea water. Their shells and armor were made of lime and were deposited on the seabed after their death. Together with removed rock rubble, they formed a layer that grew thicker and thicker over millions of years. The thick layers of limestone were pressed into solid sedimentary rock by means of heat and pressure.

The African plate began moving north about a hundred million years ago. She pressed hard on the Eurasian plate. Due to this force, the sea floor unfolded and was pushed higher and higher. The Alps gradually rose from the bottom of the sea until they finally towered over the surroundings by thousands of meters. The reef remnants and limestone layers from the sea floor became the northern and southern limestone Alps. In the north they build up the Wetterstein limestone of the Zugspitze or the Dachstein limestone in Austria. In the southern Limestone Alps, the steep rocks of the Dolomites consist of ancient reefs. There, mountaineers and fossil hunters can still find countless ammonites and other fossilized marine animals in the limestone. The Central Alps, on the other hand, consist of granite - a result of the plate collision.

Volcanic mountains

The snow-covered Kilimanjaro can be admired from a great distance. As a single mountain range, it towers far beyond the African steppe - very different from the typical folded mountains such as the Alps or the Himalayas. Because Kilimanjaro was not created when tectonic plates collided. Several volcanoes erupted in close proximity in the region around one and a half million years ago. The mighty Kilimanjaro massif rose up into the sky from the lava masses. Today its highest peak is the Kibo at 5895 meters above sea level.

There are also volcanic mountains in Germany, for example the Siebengebirge near Bonn. Several volcanoes became active here 25 million years ago and hurled their hot rock masses to the surface of the earth. Today they are long gone, but as mountains and heights of the low mountain range they are still clearly recognizable.

Incidentally, the longest mountain range on earth is of volcanic origin - it is sunk in the sea: the mid-Atlantic ridge extends over a full 20,000 kilometers through the middle of the Atlantic Ocean. The mid-Atlantic ridge is one of the mid-ocean ridges. These lie where two oceanic plates move away from each other. A gap forms on the sea floor between the two plates, from which hot magma gushes. Long and high mountain ranges form under water at such plate boundaries. In some places their peaks protrude above sea level. This is where Iceland, the Galapagos Islands and the Azores see the light of day.