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Laimer, H.J. and M¨llegger, M., 2012. Geomorphological and geotechnical causes of anthropogenically induced rockmass falls in theWachau-Danube Valley (Bohemian Massif, Lower Austria). Geografiska Annaler: Series A, Physical Geography, 94, 157-174. doi:10.1111/j.1468-0459.2012.00451.x ABSTRACT The Wachau-Danube Valley represents a transverse valley, intersecting the Variscian Bohemian Massif. Weakened rocks along fault structures led to accelerated river erosion, forming relatively steep rock slopes. The exceptional cultural position of the region generated an increasing demand for building materials. Over the centuries quarrying had a sizeable impact on slope morphology. Interdependences between quarrying and construction caused unstable rock slopes and four rock-mass falls have occurred at two quarries near Spitz (1961, 1984, 2002) and Dürnstein (2009). Rock mechanical analysis at these quarries has shown that the combination of existing geological discontinuities and artificially modified morphology is fatal in terms of slope stability. In Spitz the bedding planes within the marble had been undercut by the mining face. Additionally, two conjugated, steeply dipping joint sets formed large scale blocks sliding on bedding planes. In three major rockslides/rock-mass falls, each triggered by heavy rainfalls, a total mass of 170 000 m3 of rock failed. At the quarry near Dürnstein the geotechnical characteristics of the gneiss are also unfavourable in relation to the exposition of the mining face. After several rockfalls, 65 000 m3 were blasted away in 1909 to remove unstable rock slopes. The residual rock face was destabilized and rockfall activities culminated in an event with a total volume of approximately 15 000 m3. Remedial measures for both locations are essential to maintain transport infrastructure. Sufficiently stable conditions can only be achieved by extensive reshaping of the mining faces, which involves adapting slope geometries to naturally stable joint faces. [ABSTRACT FROM AUTHOR]

Sass, O., Haas, F., Schimmer, C., Heel, M., Bremer, M., Stöger, F. and Wetzel, K.-F. 2012. Impact of forest fires on geomorphic processes in the Tyrolean Limestone Alps. Geografiska Annaler: Series A, Physical Geography, 94, 117-133. doi:10.1111/j.1468-0459.2012.00452.x ABSTRACT We investigated geomorphic processes on two slopes (Arnspitze and Bettelwurf) burned by wildfire in the region north of Innsbruck. Both burned in 1946 and both are still characterized by severe vegetation destruction. Sparsely grass-covered rock and debris slopes have developed replacing the former dwarf pine ( Pinus mugo) shrub stands. Our aim was to establish disturbed and undisturbed erosion rates and to decide whether recent debris flows can be assigned to these historical wildfires or not. We measured fluvial erosion by means of collectors, estimated the amount of post-fire erosion from stratigraphic exposures in the adjacent talus, modelled bedload discharge with a statistical model developed in a nearby study area and quantified recent debris flow activity by combining airborne and terrestrial laser scans. We measured erosion rates of 3-30 g m−2 a−1, which is roughly ten times higher than the undisturbed sediment yields. Slopewash was higher than linear fluvial transport in the four years of our investigation. Surplus material was removed from the channels by avalanches and debris flows; both being more important for the sediment budget than fluvial action. The modelling approach allowed measured sediment yields to be transferred to larger slope parts and to calculate scenarios of pre-fire conditions. The concordance of measured and modelled yields was reasonably good; deviations may be explained by differing amounts of precipitation. Our results support the impression that current debris flow activity at the Bettelwurf was enhanced by the aftermath of the 1946 wildfire. [ABSTRACT FROM AUTHOR]

Rates of rockwall retreat and rockfall supply are fundamental components of sediment budgets in steep environments. However, the standard procedure of referencing rockwall retreat rates using only lithology is inconsistent with research findings and results in a variability that exceeds three orders of magnitude. The concept proposed in this paper argues that the complexity inherent in rockfall studies can be reduced if the stages of (i) backweathering, (ii) filling and depletion of intermediate storage on the rock face and (iii) final rockfall supply onto the talus slopes are separated as these have different response functions and controlling factors. Backweathering responds to preweathering and weathering conditions whereas the filling and depletion of intermediate storage in the rock face is mainly a function of internal and external triggers. The noise apparent in backweathering rates and rockfall supply can be reduced by integrating the relevant controlling factors in the response functions. Simple conceptual models for the three stages are developed and are linked by a time-dependent ‘rockfall delivery rate’, which is defined as the difference between backweathering and rockfall supply, thus reflecting the specific importance of intermediate storage in the rock face. Existing studies can be characterized according to their ‘rockfall delivery ratio’, a concept similar to the ‘sediment delivery ratio’ used in fluvial geomorphology. Their outputs can be qualified as trigger-dependent rockfall supply rates or backweathering rates dependent on (pre-)weathering conditions. It is shown that the existing quantitative backweathering and rockfall supply models implicitly follow the proposed conceptual models and can be accommodated into the uniform model. Suggestions are made for how best to incorporate non-linearities, phase transitions, path dependencies and different timescales into rockfall response functions. [ABSTRACT FROM AUTHOR]

Eight relict rock-slope failures (RSFs) on Skiddaw Group terrain in the Lake District, northwest England, are described. Five of the failures are rockslides, one is a product of slope deformation, and two are compound features with evidence for sliding and deformation in different sectors. As none appears to have been overrun and modified by glacier ice it is concluded that they all post-date the Last Glacial Maximum (LGM; c.21±3 cal. ka BP). Slope stress readjustments resulting from glacial and deglacial influences are considered to have weakened the slopes, and application of the term paraglacial is appropriate. Permafrost aggradation and degradation, seismic activity and fluvial erosion are among processes that may have contributed to failure at certain sites. The failures are significant as potential debris sources during future ice advances, contributing to valley widening and cirque enlargement and, possibly, for acting as sites of cirque initiation. Previously, Skiddaw Group rocks have been regarded as homogeneous and of limited resistance to the weathering and erosion associated with Quaternary glacial, periglacial and fluvial processes. These characteristics and processes have been used to explain the steep smooth slopes and rounded hills that dominate Skiddaw Group terrain. Rock-slope failure has also helped shape this terrain and should be incorporated in future interpretations of landscape development. [ABSTRACT FROM AUTHOR]

Mountain landscapes show rapid evolution, especially at high altitudes, in response to current climate changes. In addition, the greater number of routes and trails made available and the increase in tourism have caused some impacts on mountain areas. Gradual soil erosion has been observed along some hiking trails, with the latter tending to deepen, and with stronger erosion where the trail cuts the slope. Where trails cross forested areas, trees can suffer root damage from foot trampling as roots become exposed. A dendrogeomorphological study was conducted on trees along two hiking trails in upper Valtellina (Italian Alps). On the first trail, in Valle dei Forni, European larches and stone pines, mostly with exposed roots, were sampled. A mean erosion rate of 2.7 mm/a, related to deepening of the footpath, was obtained, and various degrees of root growth disturbance along the trail were observed. In particular, the growth of many sampled roots shows an increase in ring width corresponding with the moment when root exposure occurred, followed, after 3-5 years, by rapid growth suppression. The exposure of many roots has taken place since the 1980s. No significant variations in stem growth were observed, even when there were exposed and damaged roots. Along the second trail, in Valle Alpisella, exposed roots of mountain pines were analysed. A mean erosion rate of 3.2-3.7 mm/a, related to the escarpments bordering the footpath, was obtained, while no significant changes were detected in root growth. [ABSTRACT FROM AUTHOR]