The glacial series ( Latin glacies "ice") describes in Central Europe the landscape forms developed in a certain order, which arose during the Pleistocene glaciation by each advance of the glaciers under the glaciers, on their margins and in their foreland.
Components of the ideal, complete glacial series are:
- a ground moraine with a tongue basin
- a terminal moraine chain that curves around the tongue basin
- a gravel field or a sand plain in front of the terminal moraine chain
- a glacial valley in which the melt waters of the glaciers flowed off
The term glacial series is used to distinguish the forms, which are arranged according to geomorphological rules and formed by the glacier, from the glacial sediments assigned to the glaciers according to geological characteristics . A complete glacial series is created when the edge of the ice (not the ice) remains stable over a long period of time and is not repeatedly destroyed by the advancement of the glacier ice.
Glacial series in the foothills of the Alps
For a more detailed description of the formation of the landforms in this area, please refer to the article on the Alpine Foreland .
The landscape of the northern foothills of the Alps was shaped most strongly by the glaciers, which formed from the beginning of the Quaternary Age (about 2.6 million years ago) in the course of the ice ages and formed a network of ice streams that repeatedly pushed into the foothills of the Alps . There they formed extensive foreland glaciers. The northern foothills of the Alps was most strongly influenced by the Würm glacial period, which began around 115,000 years ago and ended with the melting of the glacier tongues around 20,000 years ago.
The trough-shaped basins, which were created by the erosion of the subsoil by the glacier ice, are called tongue basins because the glacier tongue was once located here. In these basins, if no drainage is possible, the so-called glacier edge lakes or tongue basin reservoirs form when the glacier retreats , such as Lake Starnberg , Ammersee , Chiemsee and Staffelsee as well as several lakes in the Salzkammergut . Typical shapes within the tongue basin in the foothills of the Alps are so-called drumlins , i.e. whale-shaped hills that indicate the direction of the glacier's thrust. There are hardly any glacial channels .
A glacier not only carries ice, but also large amounts of rock material that the glacier has previously carved out of the mountains and the foothills. When the glacier melts, meltwater flows form on its surface and below the glacier, which can carry away the stored gravel . The currents dump this so-called fluvioglacial gravel at the edge or below the glacier tongue in the form of so-called moraine walls (a distinction is made here between base, side, middle and terminal moraines, depending on the place of deposit relative to the glacier tongue). Moraines consist of rocks that are assigned to the glacial till.
The ground moraine is the material that was once transported under and in the glacier and that was deposited in the former glacier bed. The lateral moraine describes the material that is deposited on the flank of a glacier. A lateral moraine that is no longer actively supplied with material by a glacier because it has retreated for climatic reasons is called a bank moraine . In the Alps, bank moraines can often be found, which were formed during the Little Ice Age , are several meters higher than today's glacier surface and also reach far down to the current glacier tongue. Middle moraines arise from lateral moraines when two glaciers join.
In addition to the moraines on the edge and below the glacier, crevices on the glacier were filled by masses of gravel carried by the meltwater streams of the receding main glacier, which formed the kames after thawing , which also characterize the landscape of the northern foothills of the Alps.
Beyond the moraine zone is the gravel plain, in the northern foothills of the Alps above all the Munich gravel plain. It was created by the fact that when the glacier melted, enormous masses of water were released, which flushed large amounts of gravel, which the glacier had previously excavated, into the gravel plain. It got its water mostly from glacier gates , the former location of which is still recognizable today by the silting of the terminal moraine. Often the gravel surfaces are clearly terraced; more recent drains have cut so-called trumpet valleys into the older gravel surfaces. The material of the gravel plains emerges from the till. The transportability of the meltwater is much lower than that of the glacier, so that larger stones cannot be transported out of the tongue basin. Components with a smaller grain size, such as clay and sand, can be transported much further, which means that they are rarely found in gravel plains.
Glacial valleys were created by the melt water flowing parallel to the ice edge. Glacial valleys created by the meltwater as in northern Germany do not occur in the Alpine foothills; their function was taken over by the already existing large rivers Danube , Rhine , Rhone and Po or their tributaries, which carried away the meltwater from the glaciers.
Glacial series in northern Central Europe
Northern Central Europe was reached or crossed several times by the Scandinavian inland ice . The forms of the glacial series therefore follow one another from north to south in northern Central Europe:
The ground moraine landscape consists predominantly of flat to gently undulating areas on which the ice deposited the till. Tongue basins, in which the excavation of material played an important role, only occur to a minor extent and are part of the ground moraine landscape in the Scandinavian glaciation area. Since the advancing inland ice completely buried the existing landscape, the Ice Age forms and deposits are widespread in northern Germany. Glacial channels, on the other hand, are a widespread phenomenon in northern Central Europe.
The terminal moraine lines limit the ground moraine areas to the south. The terminal moraines are often patchy and less high than in the foothills of the Alps, but appear clearly as ridges in the low relief landscape. Due to the lack of gaps in northern Germany, the neutral term “ ice edge location” has established itself for the terminal moraine.
The meltwater that flowed off the sand surface collected in the glacial valley and mostly flowed to the north-west parallel to the edge of the ice. Glacial valleys are a special form for northern Central Europe.
Glacial series as a model of landscape formation
Like all models, the model of the glacial series only reproduces the real conditions in a simplified manner. In particular, it is often not taken into account that the forms of the glacial series emerge next to one another almost at the same time, while the edge of the ice remains on the terminal moraine. Furthermore, the ice must first advance to the later terminal moraines and then melt again. The processes that take place change the model of the glacial series significantly. A common variation is, for example, the spillage of ground moraine surfaces by younger meltwater.
In addition, repeated advancement of the glacier can lead to the nesting of different ancient forms of the glacial series. For example, terminal moraine lines in Brandenburg that were closely behind one another drained over the same sand areas and the same glacial valley.
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