Paraglacial slope adjustment since the end of the Last Glacial Maximum and its long lasting effects on secondary mass wasting processes: Hauser Kaibling, Austria
Andreas Kellerer-Pirklbauer and Herwig Proske and Volker Strasse
Geomorphology , 1/2010
This study indicates the possible long-lasting impacts of deep-seated gravitational slope deformation (DGSD) on erosional and mass movement processes. DGSD-features are common large-scale landforms in the crystalline basement rocks of the Central Alps of Austria. Inactive forms are related to paraglacial (nonglacial processes directly conditioned by former glaciation and deglaciation) rock slope adjustment processes acting after glacier retreat towards the end of the Late Glacial
period. The near-surface metamorphic bedrock of DGSD-features is generally disintegrated. Such rock type favours erosion and the formation of small landslides. Field data, laboratory analyses, aerial photographs, and GIS-based terrain analyses are used to describe the different geomorphic effects of an extremely disintegrated rock slope. The studied DGSD Hauser Kaibling (13.6 km2) is located in central Austria. During the Last Glacial Maximum the adjacent valley glacier reached an altitude of approximately 1900 m a.s.l. Glacier retreat in combination with the unfavourable tectono-metamorphic setting caused gravity-induced stresses to act. Subsequent sediment build-up in the main valley restabilised the slope. Linear erosion cut a number of gullies into the lower part of the DGSD. Calculated mean erosional denudation rates at incised valley sections range from 0.5 to 2.6 mm a- 1 since deglaciation. Smaller active landslides on the sides of the steep gullies draining the DGSD contribute to high denudation rates. Active landsliding is favoured by: (i) fragmented rock, (ii) steep slopes, (iii) supply of surface and subsurface water by rain and snowmelt, and (iv) human impact. Debris flows and debris-charged flood events occurred frequently in the past. During such events, material was transported from the unstable slopes to the populated alluvial fans. Thus, knowledge about the spatial distribution and the stage of development of DGSDs (active and currently inactive) provides an important basis for risk management measures.