The overview presented in the scientific background chapter reveals that the field of research on high-alpine bedrock slope instabilities is still limited, in terms of both the process-oriented and the technological part. Current process-oriented research is focused mainly on individual phenomena, such as geology, permafrost or glaciers and few multi-disciplinary approaches have been used. None of the GIS-based statistical methods or numerical slope stability modelling studies ever included the two key factors glacier and permafrost, but focused instead on topog- raphic and geological factors. However, considering the fact that these two factors are currently prone to rapid changes, they must be included in a multi-disciplinary approach for analyses of slope stability in periglacial terrain. In the field of technology and methodology, highly promis- ing advances were achieved during recent years, e.g. in LiDAR techniques, GIS-based methods or numerical slope stability analyses. A wide variety of conventional and novel data acquisition and modelling techniques have been used and tested in different projects, but only a few of these projects are actually situated in high-alpine terrain. Therefore, for most of the techniques introduced in the previous chapter, the applicability and potential at steep high-mountain faces is rarely known.
This work is based on a multi-scale approach and comprises different conventional as well as novel methodological approaches for data acquisition and the investigation of slope instabili- ties to test their applicability on high-mountain rock walls. The characteristics of the detach- ment zones of recent periglacial rockfall and rock avalanche events are considered as possible proxy information for the evaluation of essential predisposing factors and processes. The multi- scale approach consists of a regional-scale study covering the Swiss Alps and adjacent zones, considering a larger number of recent rock avalanche events and two local-scale studies concen- trating each on specific rock walls with recent slope instabilities. Existing base data covering the entire investigation area include a digital elevation model with 25 m grid spacing (DHM25 Level 2; Swisstopo, 2004), a digital lithological map (based on the Swiss Geotechnical Map, 1:200,000), digital glacier inventories of the Swiss Alps for the years 1850, 1973 and 1998 (Paul, 2004), a recent permafrost map (FOEN, 2006), orthophotos and topographic maps. Additional data was acquired within this project, especially for the two local-scale study sites based on in
situ field investigations, applying optical remote sensing techniques and by the use of digital photogrammetry and aerial LiDAR. The base data sets can be distinguished as point data and spatial data. In situ data acquisition methods mainly produce point data which provide a difficult basis for spatial exploration. For the acquisition of spatial data, a remote-sensing-based ap- proach is more suitable.
Chapter 3
As a brief summary, the different approaches concentrate on 1) a GIS-based statistical multi- factor analysis based on a rock avalanche inventory over the entire Swiss Alps, 2) a GIS-based multi-factor analysis and detailed remote-sensing-based topographic modelling of the Monte Rosa east face, and 3) geomechanical analysis and distinct element slope stability modelling of the Tschierva rock avalanche at the Piz Morteratsch.
3.2 Study sites
The different study sites are introduced here, as they represent the basis of the entire project and of the summary of research papers which follows.
3.2.1 Regional‐scale approach
During recent decades, a considerable number of rock avalanche events originating from high- mountain regions have been described and investigated in scientific studies (cf. Chapter 2.1.2). The basis for the regional-scale approach is a rock avalanche inventory containing 57 rock ava- lanche events that occurred between 1900 and 2007 in the Swiss and adjacent Alps. The de- tachment zones of the considered events are located above 2000 m a.s.l and the volumes are es- timated to be around or larger than 1000 m3. The locations of the inventoried events are indi- cated by red dots in Figure 3.1.
3.2.2 Local‐scale approaches
The east face of Monte Rosa, Italian Alps, is located at the Swiss-Italian border (Figure 3.2, A), and is among the highest and most impressive mountain faces in the European Alps (2200– 4600 m a.s.l.). During recent decades, the ice cover of the Monte Rosa east face has experienced an accelerated and drastic loss in extent. New slope instabilities and detachment zones of rapid mass movements have developed in bedrock and ice. Increased rock and ice avalanche as well as debris flow activity have been observed. Besides frequent small-volume rock and ice ava- lanche events since around 1990, an ice avalanche with a volume of more than 1·106 m3 oc- curred in August 2005, and a rock avalanche of about 0.3·106 m3 detached in April 2007 from the upper part of the flank.
The 1988 Tschierva rock avalanche detached from the western flank of Piz Morteratsch in the eastern Swiss Alps (Figure 3.2, B). The Piz Morteratsch is located within the Bernina mas- sive, Engadine, between Val Roseg and Val Morteratsch, and reaches an elevation of 3751 m a.s.l. The rock avalanche occurred on October 29, 1988, with a volume of 250,000 to 300,000 m3.
Conceptual Framework
Figure 3.1: Overview of the spatial distribution of slope failure events.
Figure 3.2: Location of the Monte Rosa east face (A) and the 1988 Tschierva