Tunnel valley

A glacial trough or a tunnel valley formed under the glacier by the erosive effect of the meltwater ( subglacial channel ). In Central Europe they are particularly common in the Scandinavian glaciation area. Typically, they are part of Grundmoränenlandschaften. By younger overprinting (eg overfill the ground moraine ), there are glacial troughs but also in glacial valleys and Sander areas.

Formation

Glacial troughs are preferentially formed when the ice cap, such as during the Pleistocene in northern Germany, against rising terrain pushes forward what a normal drainage, as it is given in valley glaciers disabled. The accumulated mainly in the summer ice age melt water on the ice looking over tube systems and columns relatively easy to find the way to the glacier base ( water has a higher density than ice). Following the pressure gradient flows in the direction of the ice edge and unites rather quickly to larger meltwater flows under the ice. Because of the glacier surface continues nachströmt water flowing under the ice water is usually under high pressure and can therefore flow uphill ( system of communicating tubes). Because of the pressure, the water flow can achieve remarkable speeds and exert a strong erosive action on the ground. If the surface of unconsolidated sediments is, such as in northern Germany, in a short time a significant amount of material can be removed. Since the melting water flow goes to zero in the winter, the channel closes by pressed from above glacial ice in the gutter. These ice blocks remain after the melting of the glacier often preserved as dead ice, preserving the gutter before the spill, for example, by melt water. After Austauen of Toteises the typical channel is created.

Form

Glacial troughs are elongated hollow forms. They are between one and 50 km long. The width varies from a few dozen to several hundred meters ( max. up to 2 km with channel bundling). Partial remember the channels in its course to meander. The deepening of the channel in the landscape also varies significantly and ranges from a few meters, and significantly more than 50 m (eg channel of Werbellin ). In South West Mecklenburg spilled channels with depth of almost 500 m are known. Depending on the groundwater level of the bottom of the channel is dry, vermoort or filled with rivers and lakes. Since the ice came in northern Germany mostly from the north, most glacial troughs are also aligned from north to south.

Proliferation of channels and channel lakes

On the surface visible glacial troughs are in northern central Europe and in Denmark widespread phenomenon, which occurs in young moraine, the ice area of the youngest, the Weichsel glaciation. In particular, the numerous elongated channel lakes give them a special scenic appeal. The valley lakes are elongated and often deep.

But also located deep underground could be detected by drilling or in the lignite mines in Lusatia many glacial troughs from the older ice ages, which on the surface are no longer completely buried and detectable.

In the foothills of the Alps, however, there are no ( or few ) glacial troughs. Because the foothills of the Alps to the north, ie in the direction of movement of the ice, abdacht, the glaciers there dewatered without the formation of glacial troughs.

Examples

• Lake Schwerin, Skinny Luzin, Demenzsee
• Havel lakes in Berlin and Potsdam to Havel, Lake Ruppin
• Grunewaldseenkette in Berlin, Scharmutzelsee, Werbellinsee
• Schwieloch, Schlaubetal west of ironworks city
• Ahrensburg tunnel valley, Brahmsee and Schlei in Schleswig -Holstein
• Meiendorfer Tunneltal in Hamburg
• Twente Achterhoek - channel
• Munsterlander Kiessandzug