Why did the ice age happen

Ice Age glaciers

On earth, warm and cold times have alternated over the past million years. During the warm periods, the ice melted and the glaciers shrank. During the ice ages, on the other hand, the temperature dropped so much that large amounts of new ice were formed. Glaciers were therefore able to spread over large areas.

At that time, large parts of northern Germany and the Alpine foothills were covered by huge glaciers. How far the glaciers reached can still be read today from the rubble hills that the glaciers left behind. The rubble made up of larger and smaller rock particles was removed in the glacier ice and deposited at the point where the ice melted again. When whole mounds of debris pile up, it is called moraines.

When the great glaciers melted during the Ice Ages, rivers and streams of meltwater formed at their lower ends. These rivers dug valleys into the ground that are now known as glacial valleys. Hollows or depressions in the landscape filled with water and turned into lakes.

What is a glacier?

Glaciers flow down from the mountains like white tongues. Others cover huge land masses as mighty ice sheets. Glaciers are mostly made up of ice and can be hundreds of meters thick and several kilometers long. Most of the fresh water on earth is frozen into ice! But how do such ice masses come about?

Glacier ice forms where it is very cold all year round. Such low temperatures prevail high up in mountains, for example in the Alps. The snow that falls there doesn't completely thaw, even in summer. The snow cover is therefore getting thicker and heavier. Under this load, the loose snowflakes are first pressed into granular firn and then into thick ice.

In the areas around the North Pole or South Pole, too, more snow falls throughout the year than can thaw again. Then, even in flat landscapes, glaciers form. The glaciers of the polar regions are thousands of meters thick. They are shaped like huge shields and are therefore called ice sheets.

Glaciers flow very slowly down the slope under the weight of their own weight. Melt water at their bottom makes it easier for them to slide across the ground. With their ice mass, they also drag sand and rocks with them that have been blown off the ground by frost.

If a glacier finally penetrates into warmer regions, its ice melts. The meltwater flows off in a trickle; with large amounts of water, a river forms. If the meltwater collects in a hollow, a glacial lake is created in it.

Glaciers shape the landscape

Wherever glaciers move, they shape the landscape. Stones enclosed in the ice act like coarse sandpaper: They grind rock from the subsurface at the edges of the glacier. The ice masses carry away the rubbed off rubble. The glacier scrapes out the rock. This creates valleys that look round like a U in cross-section and are therefore called U valleys.

Sand and boulders that are dragged along by the glacier ice remain at the edges and at the bottom of the glacier on the way down and form small and large hills. Such boulders on the edge of the glacier are called moraines.

If it is very cold for a long time, the glaciers grow and move further and further into the landscape. If, on the other hand, it becomes warmer, the ice masses melt and the glaciers retreat. The moraines of rubble remain, however. Centuries later you can still tell from them how far the glacier had penetrated. The place that the glacier once excavated and covered with its ice is shaped like a tongue. One therefore speaks of a tongue pelvis.

Shaped by the ice, flooded by the sea

It is a breathtaking sight: the rock walls on Norway's fjord coast rise up to a thousand meters. Even large cruise ships can easily enter this fantastic mountain backdrop. Not only was the surf of the sea at work here, but one thing above all: ice!

During the Ice Ages, Northern Europe was under a huge ice sheet. Huge glaciers flowed towards the Atlantic and scraped deep valleys with steep walls into the subsoil. After the end of the ice ages, the sea level rose and the water flooded the trough valleys of the glaciers. The result is the famous fjords. In Greenland, Alaska and on the west coast of Canada, fjords were also formed which, because of their depth and their protected location, are well suited as locations for harbors.

The glaciers of the Ice Age did not only create fjord coasts. The small islands in the Baltic Sea between Sweden and Finland also bear witness to the Ice Age. As the huge glaciers rolled over the land, they grinded angular rocks and mountains into smooth, round cusps. After the ice masses melted, the rounded hump landscape was washed over by the sea. The humps that did not sink into the water now jut out of the sea as small islands: the skerries. The many small islands form their very own coast, called the archipelago.

Gullies and basins that were excavated by meltwater during the Ice Ages flooded the sea after the climate warmed up. Today they have become valley-shaped bays that extend far into the country. The result is a fjord coast, as we know it from the Kiel fjord, for example. The gently undulating landscape of ground and terminal moraines also partially sank into the water on the coasts. The hills of the terminal moraines formed the coast with its typical flat and wide bays, inland there are often flat lakes. Such a coast is called the Bodden coast, as it can be found, for example, in Western Pomerania between the Lübeck and Oder bays.

Warm times - cold times

There were times on earth when large areas of land were buried under a thick sheet of ice. The ice masses even penetrated near the equator at times. In alternation with the ice ages, this planet was hit by gigantic heat waves. For millions of years it was so hot that palm trees could even grow at the North Pole. Ice and warm periods have alternated since the earth has existed. Climate change occurred long before humans inhabited the earth. And these natural climate changes left their mark.

During the ice ages, the glaciers expanded. Ice masses grinded the subsoil, planed valleys and pushed masses of debris in front of them. As long as it was cold, large amounts of water remained bound in the ice, which caused the sea level to drop. As soon as the temperatures rose again, the ice melted and the sea level rose again. Valleys and depressions filled with water, became rivers and lakes.

Animals and plants appeared or disappeared with the temperature changes. For example, many different types of dinosaurs lived in a particularly warm phase. When it got cooler, many of them died out. Animals such as mammoth, reindeer and bison were typical of the last ice age. With the rising temperatures, they disappeared from the scene or they moved to cooler regions. Reindeer, for example, still have their home in Northern Europe, Siberia and Canada.


The ice core that climatologists have drilled in the middle of the Antarctic is exactly 3,270.2 meters deep. At the very bottom the ice is almost a million years old. The three-kilometer-long ice core tells climate researchers a lot about the last eight ice ages.

It is a sensation for science: as part of the “Epica” research project, climate researchers have completely pierced the ice sheet of the Antarctic. At the Dome Concordia research station, after nine years of drilling, the researchers came across rocks and thus reached the deepest point of the hole: At a depth of 3,270.2 meters, the air and ice are 900,000 years old. The samples from this ice core will tell all kinds of new things about the earth's climate history. They contain information about the last eight ice ages and warm periods, for example about the concentration of carbon dioxide in the atmosphere.

The various layers of ice are like annual rings of the climate. Every year snow falls on the ice and forms a new layer. The ice sheet therefore consists of many layers of the year lying on top of each other. Air bubbles are trapped in these ancient layers of ice, providing information about the Earth's climate history. How much have the greenhouse gases in the air fluctuated over millennia? How did the temperatures develop over long periods of time? Answers to these questions are immortalized in the layers of ice.

In order to extract as much information as possible from the three-kilometer-long ice core, it is sawn into pieces and transported to research laboratories. The pieces are stored in the cold store until the ice can be examined more closely in the laboratory.

Climate research in a whiskey glass

Many discoveries are due to chance. The French ice researcher Claude Lorius observed how pieces of ice melted in a glass of whiskey. The scientist noticed air bubbles that were trapped in the ice. When the bubbles burst when the cubes melted, Lorius had a brilliant idea: the air bubbles were witnesses to the composition of the air. Perhaps one could research the climate history of the earth in a similar way, namely by drilling into ancient layers of ice. This idea came to Claude Lorius in 1965. In the years to come, he put his idea into practice. Large-scale research projects on Greenland and in the Antarctic examined the history of the climate with the help of ice cores. The result is presentable: The most recent drilling of Dome Concordia in the Antarctic has now even provided an insight into 900,000 years of climate history!