ACTIVOS BIOLOGICOS

The results are described in detail in Chapter 4 and in Publications I-V. The most important findings and conclusions of this thesis are summarised in this section and organised according to the research questions stated in the first chapter.

1. What are the primary factors that contribute to slope instabilities?

• The influencing factors depend on the volume of a slope instability. Large slope failures evolve over longer time periods and are therefore primarily affected by long-term changes, whereas small detachments often react to sporadic extreme events such as the extraordinary warm summer of 2003.

• No specific single primary factor was found based on our analyses, but a number of fac- tor combinations that contribute significantly to slope stability emerged. However, the two factors slope angle and a pronounced discontinuity system are included in such fac- tor combinations at all failure magnitudes.

• The change in a factor and the time scale of change are more important than the indi- vidual factors. Fast changes in a factor do not allow adequate stress redistribution within a flank and therefore, the critical shear strength may be exceeded. Glaciers, mainly changing the topography, and permafrost, mainly changing the groundwater regime and geotechnical characteristics of discontinuities, are currently the factors with the fastest changes.

• Slope gradient has a dominant influence on slope stability. The analyses have shown that gradients above 40° are prone to slope failures with a culmination of susceptibility between 45 and 60°.

• The lithological setting influences the magnitude rather than the frequency of slope fail- ures. However, lithological transition zones and the presence of a fault zone enhance the probability of a slope failure.

• Groundwater is found to be a very important factor – both for causing of instabilities due to cyclic loading and possible freeze/thaw processes and for the eventual triggering. However, hydrologic data is very difficult to acquire and even more difficult to extrapo- late spatially and at depth.

2. What are the appropriate techniques for data acquisition and measurement?

• This study makes clear that data acquisition in steep periglacial terrain is difficult and complex. A combination of remote sensing and in situ approaches was found to be most appropriate.

• Appropriate techniques for data acquisition and measurement depend strongly on the investigation scale. In situ approaches are based primarily on punctual measurements with a high level of detail, whereas remote-sensing-based approaches allow comprehen-

Conclusions and Perspecitves  • Remote sensing based approaches, including topographic as well as optical data, are

very useful for dealing with the problem of difficult access and for providing spatial data. Strong improvements in high-resolution topographic data acquisition were achieved by the combination of digital photogrammetry and airborne LiDAR. In addi- tion, time lapse DTMs provide a powerful basis for the assessment of topographic changes.

• Imagery analyses are important at all scales for the visual or automatic detection of sur- face characteristics. Repeat data sets are enormously important as they enable the analy- ses of temporal as well as spatial changes. Terrestrial photographs are useful for qualita- tive change analysis of surface characteristics, as they are, for the most part, available at higher frequency than any other base data.

• In situ field investigations are still very important for geotechnical and geomechanical investigations, as no detailed information about rock mass and discontinuity characteris- tics can be obtained from remote sensing data.

3. What are feasible approaches for the assessment of slope instabilities?

• The feasibility of an approach always depends on the available base data.

• All applied approaches are feasible. GIS-based factor analyses allow investigations to be conducted over large areas, but only factors with spatial information can be included. Numerical slope stability modelling, on the other hand, also includes point information and contributes to improved process understanding for a specific slope failure.

• Analyses of time-lapse high-resolution DTMs allow detailed topographic analyses to be made, and proved to be essential for slope stability analyses.

• Kinematic analyses are a powerful tool for the assessment of the failure potential, as the structural geology is one of the most important factors for slope instabilities.

• Numerical slope stability modelling is useful for re-analyses of a slope failure and sensi- tivity analyses of factors to improve process understanding. However, its use is often limited in high-mountain terrain because of a lack of information.

4. What is the scale-dependence of the different factors and analysis methods?

• The factors groundwater and structural geology could be investigated only on a local scale, and spatial extrapolation is difficult if not impossible.

• It is possible to investigate the factors geology, topography and glaciology on a large scale, however, their settings on a small scale, such as geological transition zones, are also important for slope stability analyses.

• The smaller the volume of a slope failure, the more limited the influencing area and fac- tors, and hence, the higher the resolution of the base data sets should be.

Chapter 6 

• Numerical slope stability modelling is restricted to small areas, no area-wide investiga- tions can be performed.

• GIS-based statistical analyses can be performed on a local and a regional scale, depend- ing on the basis data. However, these analyses enable factor analyses to be made, at ex- clusion of process modelling.

• Kinematic stability analysis can partially bridge the gap between detailed small area process analyses and simple area-wide factor analysis.

In conclusion, this study has shown that advanced and combined technology applied at differ- ent scales can effectively contribute to improved assessments of slope instabilities, which is par- ticularly important in view of ongoing glacial and periglacial changes. This is one of the first studies that includes the factors permafrost and glacier in GIS-based statistical analysis as well as finite element stability modelling. A better understanding of predisposing factors has been gained at different levels of detail and these findings provide a fundamental basis for prospec- tive slope instability susceptibility analyses on a regional scale.