How multiple foliations may control large gravitational phenomena: A case study from the Cismon Valley, Eastern Alps, Italy Luca Zorzi ⁎, Matteo Massironi, Nicola Surian, Rinaldo Genevois, Mario Floris Department of Geosciences, University of Padua, Via Gradenigo 6, 35131 Padova, Italy abstract article info Article history: Received 4 July 2012 Received in revised form 15 October 2013 Accepted 3 November 2013 Available online 12 November 2013 Keywords: Foliated rock masses Structural geology LiDAR data Last Glacial Maximum The right slope of the High Cismon Valley (Trento Province, Italy), carved into the poly-deformed phyllites of the South Alpine Basement, shows evidence of differential Quaternary slope evolution which highly depends on how the slope intersects the inherited structures. In the study area, the regional schistosity outlines a kilometer-scale NNW–SSE trending fold, with close flanks and an axial plane dipping to the NE. The structure obliquely intersects the NNE–SSW trending slope so that the northern part of the slope follows the upper limb of the fold and the southern sector coincides with the lower limb and the hinge. The secondary axial-plane foliation is typically incipient at the fold flanks, and much more pervasive and fan-shaped near the hinge zone. This foliation, as well as the asymmetric polyharmonic secondary folds, has significant consequences on rock mass mechanical properties and on mechanisms and timing of the gravitational phenomena developed along the slope. In particular the Joint Compressive Strength (JCS) and the Geological Strength Index (GSI), obtained on stable outcrops outside the deforming area, display a decrease from north to south. This points to a progressive deteri- oration of the rock mass strength which directly reflects the influence of the pre-existing fabric. The results obtained by the analysis of LiDAR-derived digital elevation model show evidence of two different gravitational movements, located in the northern and southern sectors of the slope respectively. The northern side is charac- terized by an ongoing deep-seated gravitational slope deformation (DSGSD) likely triggered by post-glacial unloading, derived from the retreat of the ice tongue that filled the Cismon Valley during the Last Glacial Maxi- mum (LGM). Conversely, the southern part of the slope is the expression of a fully evolved pre-LGM gravitational collapse. This heterogeneous behavior of the slope is most likely controlled by the secondary foliation and asym- metric polyharmonic folds, the former being of paramount importance for the release of the mobilized mass at the crown area, and the latter easing or impeding the downslope movement. Although it is widely accepted that the regional foliation is the dominant controlling factor of DSGSDs on poly-deformed and highly foliated metamorphic basement, our work suggests that the secondary foliation, as well as parasitic folds, may also have remarkable effects on slope evolution if favorably oriented and sufficiently pervasive. © 2013 Elsevier B.V. All rights reserved. 1. Introduction Deep-seated gravitational slope deformations (DSGSDs) are very common in the Alps, and in the last decades several phenomena have been investigated in detail (Dramis, 1984; Mortara and Sorzana, 1987; Crescenti et al., 1994; Dramis and Sorriso-Valvo, 1994; Crosta, 1996; Agliardi et al., 2001; Bistacchi and Massironi, 2001; Crosta and Agliardi, 2003; Massironi et al., 2003; Ambrosi and Crosta, 2006; Soldati et al., 2006; Agliardi et al., 2009; Massironi et al., 2010; Ghirotti et al., 2011; Agliardi et al., 2012). DSGSDs have been defined as a type of mass- movement whose depth is a relevant fraction of the slope size, and whose displacement is small in comparison with the depth of the displaced mass (Crescenti et al., 1994). The deformation mechanism re- lated to these phenomena is commonly referred to as creep (Radbruch- Hall, 1978; Hutchinson, 1988), and is characterized by low to extremely low deformation rates (Cruden and Varnes, 1996). These phenomena are strongly conditioned by time-dependent creep deformation which generates specific landforms such as double ridges, scarps and counterscarps (Agliardi et al., 2001). Their initiation is thought to have taken place after the retreat of the Pleistocene glaciers that left behind unstable over-steepened slopes (Nemcok and Pasek, 1969; Dramis, 1984; Augustinus, 1995; Dikau et al., 1996; Kellerer-Pirklbauer et al., 2010; Ambrosi and Crosta, 2011). In addition, high relief, active tecton- ics and seismicity can be considered as genetic factors of deep-seated gravitational movements. It is widely accepted that the evolution of DSGSDs is strongly con- trolled by the structural setting of the bedrock. In particular, a close re- lationship between gravitational morphostructures and brittle tectonic features has been demonstrated (Zischinsky, 1966, 1969; Nemcok, 1972; Radbruch-Hall, 1978; Savage and Varnes, 1987; Chigira, 1992; Crosta, 1996; Agliardi et al., 2001). Few studies, however, have taken into account how, at the slope scale, the inherited ductile framework (i.e. regional foliations and folds) in foliated metamorphic rocks Geomorphology 207 (2014) 149–160 ⁎ Corresponding author. Tel.: +39 0458279119; fax: +39 0498279134. E-mail address: lucazorzi84@gmail.com (L. Zorzi). 0169-555X/$ – see front matter © 2013 Elsevier B.V. All rights reserved. http://dx.doi.org/10.1016/j.geomorph.2013.11.001 Contents lists available at ScienceDirect Geomorphology journal homepage: www.elsevier.com/locate/geomorph