Stage 3 | Vejle – Sønderborg / Borrowed land from the Scandinavian highlands

The last stage on Danish soil takes us over the youngest rocks in the Danish subsurface, which are Miocene in age, about 20-10 million years old. When these sediments were deposited, the North Sea was an embayment that ran between Norway and Scotland to Denmark, but not to northern France (see figure). And during this period, this shallow sea was filled up with sand and clay that was eroded from the highlands of Scandinavia; borrowed land.

Borrowed land

These sediments from Scandinavia's highlands were transported via large rivers and deposited in deltas, causing the land to grow slowly, turning the shallow sea into swamps and sandbars. And even a few meters of sea level rise, resulting from changes in the volume of ice at the poles, was enough to flood the newly claimed land. Much of northwestern Europe, including the Netherlands, Flanders, and northwestern France, still consists of such 'borrowed land'. But unlike Denmark in the Miocene, we are now able to keep rising seawater away from this borrowed land (for now at least) by building dikes. One danger, however, is that the soils and sediments behind the dikes will compact and subside and it is no longer receiving new sediments – we don't want to flood the cities and fields every few years to bring in new silt. So there are concerns about the future of the borrowed land.

Denmark under an icecap

The last hundreds of thousands of years of Danish geological history were dominated by the ice ages. During several episodes, Denmark was completely or partially covered by a pack of ice several hundred meters thick, which in their heydays extended to central Germany, the Netherlands and southern England. When the Danish lands were not covered by ice, they formed dry tundras and steppes, home to the famous Pleistocene Ice Age inhabitants such as mammoths. In the last 10,000 years we have gone from a "glacial" to an "interglacial" and the ice has retreated. One of the effects of the disappearance of the enormous mass of a kilometer or more of land ice is that the earth's crust slowly rebounds. And to this day, the borrowed land of Denmark is also still slowly rising, at a rate of one millimeter per year.

I am a geologist and I study plate tectonics and the driving mechanisms in the Earth’s mantle, mountain building processes, and the geography of the geological past. I enjoy geological fieldworks all over the world, and translating the results to science and to a broad public. Read more about Douwe.

Douwe van Hinsbergen