The types of glacial erosion landscapes determined by the basic relief

Abstract

Article in German.

ORIGINAL TITLE: Die vom Grundrelief bedingten Typen glazialer Erosionslandschaften

The type of mountain-landscape formed by glacial erosion which is generally treated in our textbooks and which is characterised by deep trough-valleys and hanging glacial cirques and tributary troughs is frequent in the Alps. But it is neither the only nor the most simple shape of the mountain-Iandscape formed by glacial erosion.

If mountains are but little dissected, that means that the valleys are not as deep as 400 to 500 m, then such mountains, if they rise above the snowline, use to develop plateau-glaciation, and wide regions of roches moutonnés arise, if the process continues for a long time.

If the mountains are dissected to a moderate degree, i. e. more than 400 to 500 m, but less than 800 to 1 000 m, then such mountains are formed by strong valley glaciation to landscapes of a characteristic kind. I should like to call them glacial -erosion -reliefs of moderate depth. The cirques and the troughs are situated here nearly in the same level of the relief. Steps occur, but they are low in comparison with the height of the trough-walls or cirque-walls. So we can say: the relief is one-storied.

The glacial-erosion-relief of moderate depth may be narrow or wide. That is dependent on the general character of the valley cutting. Examples are shown especially from America.

If the valleys are deep, i. e. more or much more than 1 000 m deep, and if the general character of the dissection is narrow, then results the deep and narrow glacial-erosion-relief. It has very deep so called simple troughs as in parts of the western Alps, the Caucasus, the Himalayas. These troughs begin with cirquelike trough-heads, the walls of which are much higher, however, than the walls of normal cirques. Normal cirques are seldom in these landscapes through lack of flat space.

If the deep glacial-erosion-relief, which is more than 1 000 m deep, has more gentle areas in the height, then results the two-storied glacial-erosion-relief.

But there are three important kinds of this two-storied glacial-erosion-relief. The first is the extre mely two-storied glacial-erosion-relief or two-storied glacial-erosion-relief with fjeld-niveau such as in the Sierra Nevada of California or in the Norwegian Highlands. Here the preglacial relief was distinctly gentle in the height and was dissected by deep narrow valleys in the depth.

 The second type of the two-storied glacial-erosion-relief is characterised by trough-shoulders which separate the deeper relief-story of the main-troughs from the higher story of the cirques and tributary troughs. These pronounced flat trough-shoulders have been proved by many studies in the Alps to be transformed ancient valley-terraces.

But there is a third form of the two-storied glacial-erosion-relief. Here the cirques and tributary troughs in the height and the main-troughs in the depth are separated from one another only by so-called ,,Schliffbords". These are steep surfaces of glacial smoothing which cannot be interpreted as valley-terraces. In the two-storied glacial-erosion-relief with .,Schliffbords" there is no evidence of a valley-in-valley-plan of the preglacial relief.

The differences of forms here mentioned in my opinion are firstly dependent upon the character of the preglacial relief and not upon differences of the rocks or upon the duration of glacial action. Some evidence is given to prove this.