Norddeutsche Tiefebene

North German Plains


The Norddeutsche Tiefebene (North German Plain) is actually called the Norddeutsches Tiefland (North German Lowlands) and is the large geographical area between the North Sea, the Baltic Sea and the Central European low mountain range. In fact, people in Western Germany usually associate this term with the region between Hanover and Hamburg, but that is only a very small part of it. If you look at a map, the low mountain ranges are actually quite far north here. To the west, the Westphalian Basin and the Lower Rhine are also included, meaning the lowlands extend almost as far as Bonn. To the east, the southern boundary is the Ore Mountains and the southernmost point is near Zwickau. This makes it the largest region in Germany with a more or less uniform geology.

The area is a lowland region; it was covered by massive glaciers on several occasions during the various ice ages and is therefore covered by thick Quaternary deposits. These deposits consist of sand and stones, and in many areas the groundwater lies close to the surface. Overall, these are very poor conditions for karstification. In other words, there are practically no natural caves here. However, there is mining activity, specifically for salt, potash, lignite, hard coal, crude oil and iron ore. This is due to the basin structure. Above a crystalline basement lie 3 to 4 kilometres of Mesozoic sediments, beginning with the Zechstein.

In the Zechstein strata there are salt deposits of considerable thickness. The density of the salt is lower than that of the overlying strata. Furthermore, salt begins to flow at a pressure of just 100 kg/cm². Consequently, the salt soon began to flow, particularly during the Upper Jurassic and Lower Cretaceous periods. Salt hills formed, which then penetrated the overlying strata and formed salt domes (diapires). The forces from below often caused hill-like bulges to form above the salt domes, where the karst-prone layers of Muschelkalk and Jurassic rock were locally transported upwards to the surface.

As is common in Europe, hard coal was deposited as seams within the sedimentary layers, predominantly during the Carboniferous period. Mining usually began at locations where the coal had reached the earth’s surface as a result of salt tectonics. The formation of crude oil is also linked to salt tectonics; the oil from the bitumen-rich source rocks rises upwards and is collected in so-called ‘traps’. These are water-impermeable marl layers that are bent upwards by the diapirs, thus forming an upward-facing dome around the diapir. The iron ore generally originates from the Middle Jurassic, which is also known as the Brown Jurassic due to its iron content. Here too, mining usually began where the layers of the Brown Jurassic had reached the Earth’s surface through salt tectonics.

Lignite is probably the only mineral resource not linked to halotectonics. Across the region, there are numerous areas with significant lignite deposits. These include the Rhineland, Helmstedt, Central Germany and Lusatia; until a few years ago, lignite was mined and used to generate electricity and district heating on a large scale in these areas. Most of these operations have now closed, not because of a lack of profitability, but for the reduction of CO2 emissions and because of protests against the huge opencast mines. However, this also means that there are now a large number of museums dedicated to this topic. As there is no underground mining, there are no show mines, those museums are industrial museums, nevertheless we listed them.

Naturally, a plain is much easier to conquer in the event of war than a mountainous region. Consequently, massive bunker complexes and defensive structures were built during the world wars of the 20th century. Added to these are the air-raid shelters in many major cities. It can therefore be said that the majority of the underground attractions in this region are bunkers.