Gravel terrace
Gravel terraces or embankment terraces can be found in the valleys of almost all low and high mountain ranges , but also in the foothills of the Alps (sometimes with extensive gravel roofs ) and sometimes even in the hill country . The terraces are predominantly ice-age formations from the Pleistocene , when the often very water-rich rivers deposited large masses of rock in the valleys or in the foreland and later or in the next warm period cut into these gravel bodies again.
Glacial climatic cause
This glacial-climatic explanation goes back to research by the paleontologist Wolfgang Soergel in the 1920s: During the glacial times, gravel was mainly graveled because more rubble was brought in than the rivers could carry away. The erosion then took place in the interglacial due to the constantly flowing river water.
In southern Germany and Switzerland , it was the predominantly northward-facing rivers that deposited their flood- laden cargo to the side before the ice pushed out of the Alps , as did in the broad long valleys of Austria . There are also several such gravel terraces at different altitudes, in the Vienna Basin even four up to 300 meters above sea level. In the mountains, the terraces, which are often more than 100 meters thick, are built up of sandy or silted fine to coarse gravel and usually contain more allochthonous rocks than local rocks. The proportion of the latter is even lower in the foreland.
Other causes
In northern Germany , where the ice sheet brought a lot of rock debris from Scandinavia , the thalassostatic interpretation also plays a role, according to which fluctuations in the sea level changed the respective level of erosion - starting from the river mouth ( Frederick Zeuner 1959).
Tectonic uplifts and subsidence come into question as the third cause of the decomposition of gravel bodies in terraces . Such were z. B. Detected in the Rheingraben in 1910 by Carl Mordziol and in 1926 by Heinrich Quiring . Here too (as in the Vienna Basin) the oldest terraces are high and the youngest are deep.
See also
literature
- Hans Murawski : Geological dictionary (keyword high or gravel terrace), Enke-Verlag, Stuttgart 1977