Traces of the ice age

When cycling in Denmark, you clearly notice that hills exists. And that there is something called “flat as a pancake”. If you are getting up from East Jutland’s deep fjords and river valleys, there is always a steep hill that you have to climb. Afterwards you climb to the highest hill tops in the lake-high land area (Søhøjlandet) in the middle of Jutland, where you can see 30-40 km to all sides from Ejer Bavnehøj and Yding Skovhøj can see 30-40 km. You continue west, cross the ice front line and arrive on the melt-water plains. Suddenly the landscape is flat, the sky is big, a few places interrupted by a drumlin, which are the remnants of former ice age moraine landscapes. In the border zone between valley and plateau several deep erosion valleys were cut during and after the ice age, such as in the photo of Rebild Bakker.

Terminal moraine

During the Weichselian glaciation, the ice repeatedly forced itself from north and east across Denmark. On its way, the ice gathered and pushed material in front of it – or transported it on top or inside. When a three kilometre tall ice sheet moves, there are really powerful forces at play. The material that is being pushed up at the end and on the side of a glacier is called a terminal moraine. It consists of a rough scrape of the soil that the ice has moved across. Some places terminal moraines consist of large amounts of sand, gravel, and rocks, while other places have flakes of clay. On the picture below is the moraine landscape at Langåsen.

Kettle hole

In hilly moraine landscapes you often find deep holes – almost craters – in the landscape. Some places have water at the bottom, while others do not. It is imprints of big lumps of ice – dead-ice – that broke off the main ice during the final melting. These lumps of ice were covered by gravel, sand, and soil and thus isolated from the warmer surroundings after the ice age. Through thousands of years these lumps of dead-ice slowly melted away and left a hole in the landscape corresponding to the ice that was originally left.

Tunnel valley

When the ice melt – in warm periods and in the summer – the enormous water masses would of course have to move. The water found its way into tunnels and trenches in the layer under the ice and gushed towards west. The forces of the water created deep tunnel valleys that among other places can be seen in East Jutland. Some tunnel valleys are several kilometres wide and expanded over a long period of time, where the water repeatedly shifted course. Under Aarhus lies a network of waterways and they function as the reservoirs, where we get our drinking water today.

Outwash plains

When all the melt-water broke through the glacier tunnels, it gushed out over the ice-free landscape and further west. The water changed course constantly. The water transported sand, gravel, and rocks. The heaviest material was deposited closest to the ice. The endless transport took part in leveling the landscape, which made it very flat – with a small slope from east towards west.

The ice as a bulldozer

During the cold periods of the Weichselian glaciation, the ice masses grew and moved across the landscape. Like a bulldozer, the ice pushed rocks, gravel, and remains of dead animals in front of itself. Where the ice reached, it deposited the gathered material as so-called terminal moraines. During warmer periods the ice melted away. The water gushed with great force through the landscape and led some of the material into the ocean, while some was deposited on land. Today, we  collect gravel from these sediments, and we find remains of the past animals in the form of teeth, skulls, and bones.

The ice as a history book

The inland ice in Greenland is like a big history book that tells about the climate fluctuations of the past. By examining ice cores drilled from the inland ice, researchers have learned about ice ages and warm periods 800,000 years back. It is the content of oxygen-isotopes 18O and 16O in the ice, which indicates how the climate has changed through the years. The percentage-wise concentration of 18O is a measure of temperature. Low concentrations indicate a cooler climate.