Abstract
Abstract. Rock avalanches are extremely destructive and uncontrollable events that involve a great volume of material (> 106 m3) and several complex processes, and they are difficult to witness. For this reason the study of these phenomena using analog modeling and the accurate analysis of deposit structures and features of laboratory data and historic events become of great importance in the understanding of their behavior.The main objective of this research is to analyze rock avalanche dynamics and deformation process by means of a detailed structural analysis of the deposits coming from data of 3-D measurements of mass movements of different magnitudes, from decimeter level scale laboratory experiments to well-studied rock avalanches of several square kilometers' magnitude.Laboratory experiments were performed on a tilting plane on which a certain amount of a well-defined granular material is released, propagates and finally stops on a horizontal surface. The 3-D geometrical model of the deposit is then obtained using either a scan made with a 3-D digitizer (Konica Minolta VIVID 9i) or a photogrammetric method called structure from motion (SfM), which requires taking several pictures from different point of view of the object to be modeled.In order to emphasize and better detect the fault structures present in the deposits, we applied a median filter with different moving window sizes (from 3 × 3 to 9 × 9 nearest neighbors) to the 3-D datasets and a gradient operator along the direction of propagation.The application of these filters on the datasets results in (1) a precise mapping of the longitudinal and transversal displacement features observed at the surface of the deposits and (2) a more accurate interpretation of the relative movements along the deposit (i.e., normal, strike-slip, inverse faults) by using cross sections. Results show how the use of filtering techniques reveals disguised features in the original point cloud and that similar displacement patterns are observable both in the laboratory simulation and in the real-scale avalanche, regardless the size of the avalanche. Furthermore, we observed how different structural features, including transversal fractures and folding patterns, tend to show a constant wavelength proportional to the size of the avalanche event.
Highlights
Rock avalanches, or sturzstroms (Heim, 1932), are defined as an extremely rapid, massive, flow-like motion of fragmented rocks derived from a bedrock failure (Hungr et al, 2001)
The second one is made of strikeslip faults parallel to the flow direction and present at the lateral margins of the deposit
The main features observed in the digital elevation model (DEM) are recognizable on the gradient map, but a series of structures that are masked on the DEM image can be identified in the gradient image
Summary
Sturzstroms (Heim, 1932), are defined as an extremely rapid, massive, flow-like motion of fragmented rocks derived from a bedrock failure (Hungr et al, 2001). A great volume of material (> 106 m3) is involved, and the flowing mass can reach velocities on the order of tens of meters per second They can travel long distances, on the order of kilometers, and cover an area over 0.1 km (Hsü, 1975). Authors have proposed different possible causes, which could explain the high mobility of these phenomena, such as the influence of the large destabilized volume (Heim, 1932; Hsü, 1975; Scheidegger, 1973; Nicoletti and Sorriso-Valvo, 1991), the momentum transfer within the rear and the front of the flowing mass (Van Gassen and Cruden, 1989; Manzella and Labiouse, 2009), or the fragmentation of the spreading mass (Heim, 1932; Davies, 1982; Davies and McSaveney, 1999; Locat et al, 2006). One of the most used is the Fahrböschung concept, which was introduced by Heim (1932) to estimate the maximum runout of rock avalanches or landslides (Scheidegger, 1973; Hsü, 1975; Davies, 1982) and which is defined as the angle of the straight line connecting the head of the scar to the end of the deposit
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