Slope tectonics: a short introduction

Abstract

Geomorphology, structural geology and engineering geology allow description of the main characteristics of a slope in distinct ways that can be combined to provide a complementary view of the operative slope processes. The subjects presented in this Special Publication include: slope morphology and evolution; mechanical behaviour of the material; modes of failure and collapse; influence of lithology and structural features; and the role played by controlling factors. This Slope Tectonics volume comprises a series of very different contributions that attempt to underline a multidisciplinary approach that should form the framework of slope instability studies.Slope Tectonics is adopted in this volume to mean deformation that is induced or fully controlled by the slope morphology and that generates features that can be compared to tectonic features. The stress field in a slope is the result of gravity, topography and the geological setting created by an ensemble of geodynamic processes. Active tectonics (also called neotectonics) generates a stress field that can control slope processes; a strong feedback existing between geological history, tectonics, lithology, geomorphological evolution and topography.As a consequence, a list of factors and their relative influence can be presented.

Rock slope instability and erosion: toward improved process understanding

“…Thus, fracture generation has been investigated as the result of the environmental stress history in geology and geomorphology, partly modulated by incision and topographic stress evolution (Leith et al, 2014a;Shrestha and Broch, 2008). Resultant fracture patterns control the degree of discontinuity heterogeneity, anisotropy, and nonlinear mechanical behaviour over millions of years (Jaboyedoff et al, 2011). In technical terms, the geosciences can help to parameterize rock (DIANE) materials and their dynamic temporal and spatial evolution in a way the engineering community cannot.…”

“…Memory effects record information on prior stress fields over many million years. Resulting parameters such as fracture density and orientation are among the best correlated factors for rock slope erosion (Sass, 2005;Moore et al, 2009;Jaboyedoff et al, 2011). Thus, the tectonic, ambient stress, and incision history may often be more relevant for the rates of rock slope erosion than more readily available factors such as lithology or aspect.…”

“…(Bottino et al, 2002;Geertsema et al, 2006;Haeberli et al, 2004;Huggel et al, 2008;Lipovsky et al, 2008;Sosio et al, 2008). Accordingly, enhanced activity of cliff falls (10 4 -10 6 m 3 ), block falls (10 2 -10 4 m 3 ), boulder falls Mechanical and hydraulic parameters typically differ by less than one order of magnitude in different orientations (Jaboyedoff et al, 2011;Jaeger et al, 2007;Rong et al, 2013) Directional dependence Orientation of slope relative to fracture patterns (i.e. daylighting) is often more important than material strength…”

“…friction angle) (Augustinus, 1992;Moore et al, 2009;Selby, 1980;Selby, 1989;Shrestha and Broch, 2008 (Bowman et al, 2012;Erismann and Abele, 2001;Hewitt et al, 2008;Krautblatter et al, 2012b) Size effects critically influence the mobility of rock avalanches Topography and trajectory effects Topography and physical properties of the trajectory critically affect the mobility of rock avalanche runout Due to the lower speed and energy of soil slope failures topography and trajectory effects are less important (Dufresne, 2012;Evans et al, 1989;Hewitt et al, 2008) Temporal nonlinear controls Persistence of slopes Time scale typically 0.1-10 Ma Time scale typically 0.01-10 ka (Ballantyne, 2002;Ballantyne and Stone, 2013;Hall et al, 2012;McEwen and Matthews, 2013) Memory effects, i.e. stored in discontinuity patterns Time scale typically 1-1000 Ma Time scale typically 0.1 to 10 ka (Hall et al, 2012;Jaboyedoff et al, 2011;Jaeger, 1979)…”

Improvements in 3-D digital mapping for geomorphological and Quaternary geological cartography

“…Deep-seated gravitational slope deformations (Sackung) and rockslides affect both valley flanks and may play an important role in the development of these morphostructures, which are probably the visible expression of slope tectonics processes (e.g. Jaboyedoff et al, 2011). Three-dimensional digital stereoscopic photogrammetry, together with quantitative geomorphological analysis, will make it possible to assess the genesis of these morphostructures.…”