How were the Alps formed?

Some mountains rise thousands of metres, with rugged slopes and a permanent covering of ice and snow. Others, by contrast, are low hills that gently shape the landscape.

Germany’s highest mountain, the Zugspitze, is 2,962 metres high and lies in the Alps. The Alps are relatively young, and are classified as high mountains. The Black Forest, by contrast, is much older and was once much higher than it is today. Over millions of years, wind and weather have worn down its peaks. Feldberg, its highest point, reaches only 1,493 metres. The Black Forest is therefore classified as a low mountain range. The highest mountain peaks on Earth are part of mountain ranges. These include the Alps in Europe, the Himalayas in Asia, the Andes in South America and the Rocky Mountains in North America. The highest peaks are in Asia: Mount Everest in the Himalayas (8,848 metres), K2 in the Karakoram (8,611 metres) and Kangchenjunga, also in the Himalayas (8,586 metres). The depths of the sea contain depressions and trenches. Since almost 71 percent of Earth’s surface is covered by water, most people never get to see these depths. The Mariana Trench in the northern Pacific Ocean reaches down to 11,034 metres. The difference between the deepest and highest points on Earth’s surface is therefore almost 20 kilometres.

Earth is a sphere. It has a diameter of 12,742 kilometers and a circumference of 40,075 kilometers at the equator. It rotates once on its axis every 24 hours and orbits the Sun once a year. It is about 4.5 billion years old. Over this long period, it has changed constantly—and it is still changing. However, this process happens very, very slowly.

The Earth is made up of several layers. Deep inside are the inner and outer cores. The inner core is solid and consists mainly of iron and nickel. It is about 6,000° C hot. The Earth’s core is surrounded by the mantle. This consists of thick, liquid rock and is about 2,900 kilometers thick. The temperature gradually decreases toward the surface, eventually reaching just a few hundred degrees.

The Earth's mantle is enclosed by the Earth's crust. The crust is very, very thin, only 35 kilometres thick on average. New mountain ranges and valleys are constantly forming in this thin crust, and continents and oceans are shifting.

Continents and oceans shift in relation to one another by only a few centimeters a year. But over a million years, 5 centimeters a year adds up to 50 kilometers. We normally don’t feel these slow changes. Only when volcanic eruptions and earthquakes occur do we realize that something is moving in Earth’s crust.

Earth’s crust is the outer layer of a region called the lithosphere. The lithosphere is about 100 kilometers thick on average. It consists of enormous plates that fit together like a giant puzzle. These are called lithospheric plates or continental plates.

The Earth’s mantle lies beneath these plates. At this depth, the temperature is so high that all the rock melts. The Earth’s lithospheric plates therefore float on the hot material below, so to speak. They move very slowly but continuously.

They also push against each other. Sometimes, as the plates move, one plate is pushed beneath another. In some places, hot, molten magma from the Earth's mantle is then forced up to the surface. This forms a volcano.

When two tectonic plates are pushed against each other, enormous pressure builds up, which can repeatedly cause severe earthquakes.

The pressure also pushes up new mountain ranges. It causes the outer parts of the Earth's plates to fold and deform, like two pieces of pancake being pushed together. The pressure keeps lifting them higher.

The same was true of the Alps, the longest and highest mountain range in Europe. Their formation began about 135 million years ago. Where high peaks tower today, there was once an ocean 1,000 kilometers wide. Then two tectonic plates, known as the Eurasian and African plates, moved toward each other.

The ocean grew narrower and narrower until it finally disappeared altogether. But the two plates continued moving. Under the enormous pressure, their edges became locked together. Masses of rock rose up and pushed over one another, forming folds and cracks. It all happened very, very slowly. But a new mountain range was formed. It rose by only about 5 millimeters a year.

The European and African tectonic plates are still moving towards each other today. They approach each other by about 5 centimetres per year. That is why the formation of the Alps is not yet complete. They grow by about 1 to 2 centimetres in height each year. However, erosion removes most of this growth at the same time.

The peaks of the Alps eventually rose to as much as 30 kilometers into the sky. Today, however, the highest peaks are still only about 4,000 to 4,800 meters high. That’s because mountains are not only being pushed higher; they are also constantly being worn down.

This is caused by a process called erosion. Water plays a major part in it, falling on the mountains as snow and rain. As it runs down the mountain, it carries away tiny particles. Water also seeps into small cracks. When it freezes, it expands and splits hard rock apart.

In strong sunlight, the rock heats up. It also expands and eventually cracks. Wind also carries away small pieces of a mountain and deposits them elsewhere.

When the pressure between the Earth’s plates eases, the mountain stops growing taller. Erosion eventually turns a high mountain range into a lower range of rounded mountains, which slowly but surely continues to lose height. These changes can only be measured over very long periods of time.

For example, we can see that the water in rivers flowing down from mountains is always discolored grey because fine particles of rock are dissolved in it. We see rocks tumbling down the mountains and the channels carved into the rocks by water.