Evidence for pre-Pleistocene landforms in the Eastern Alps: Geomorphological constraints from the Gurktal Alps

We present evidence for a series of pre-Pleistocene landforms on hand of a new geomorphological map for the Gurktal region of the Eastern Alps. The Gurktal Alps region is the westernmost region of the Eastern Alps that escaped the glacial reshaping in the Pleistocene. Its morphology therefore preserves evidence of older landforms in closer proximity to the central part of the range than any other region in the Alps. The region is therefore useful to document aspects of the geomorphological evolution for the Eastern Alps during both, the Pleistocene glaciations and the earlier uplift history. Our mapping approach is twofold. We applied stream-power analysis outside the glacially overprinted areas to detect and classify spatially distinct quasi-stable stream segments, which we expanded to planar objects using slope analysis combined with field mapping. Our mapping results document four palaeo-surfaces located roughly at about 1500 m, 1200 m, 900 m and about 800 m above sea level. We correlate these levels with well-known palaeo-surfaces from the eastern end of the Alps and suggest that they can be interpreted in terms of more than 1000 m of surface uplift in the last six million years. Channel analysis and the distribution of Pleistocene gravel terraces suggest that the main trunk of the river Gurk was diverted from the Wimitz valley in the Rissian. Furthermore, steam-power analysis documents an ongoing activity of the Görschitztal fault and some inferred Pleistocene activity of a north-west trending fault close to the township of Gurk.