Glacial meltwater valley

An Urstromtal (plural: Urstromtäler) is a type of broad glacial valley, for example, in northern Central Europe, that appeared during the ice ages, or individual glacial periods of an ice age, at the edge of the Scandinavian ice sheet and was formed by meltwaters that flowed more or less parallel to the ice margin. Urstromtäler are an element of the glacial series. The term is German and means "ancient stream valley". Although often translated as "glacial valley", it should not be confused with a valley carved out by a glacier. More accurately some sources call them "meltwater valleys" or "ice-marginal valleys".

Important for the emergence of the Urstromtäler is the fact that the general lie of the land on the North German Plain and in Poland slopes down from south to north. Thus the ice sheet that advanced from Scandinavia flowed into a rising terrain. The meltwaters could therefore only flow for a short distance southwards over the sandurs (outwash plains) before having to find a way to the North Sea basin that was parallel to the ice margin. At that time, the area that is now the North Sea was dry as a result of the low level of the sea.

As elements of the glacial series, Urstromtäler are intermeshed with sandur areas for long stretches along their northern perimeters. It was over these outwash plains that the meltwaters poured into them. Urstromtäler are relatively uniformly composed of sands and gravels; the grain size can vary considerably, however. Fine sand dominates especially in the upper sections of the Urstromtal sediments. The thickness of the Urstromtal sediments also varies a great deal, but is mostly well over ten metres.

Urstromtäler have a wide and very flat valley bottom that is between 1.5 and 20 kilometres wide. The valley sides, by contrast are only a few to a few dozen metres high. The bottom and the edges of an Urstromtal may have been significantly altered by younger processes, especially the thawing of dead ice blocks or the accumulation of sand dunes. In the post-glacial period, many Urstromtäler became bogs due to their low lying situation and the high water table.

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