Battista Matasci

Stability Assessment, Potential Collapses and Future Evolution of the West Face of the Drus (3,754 m a.s.l., Mont Blanc Massif)

A structural analysis was performed in the field and using Terrestrial Laser Scanning point clouds. The failure mechanisms and volumes of the collapses in the last decades have been studied and calculated to be able to assess the future evolution of the stability of the west face of the Drus.

Geological mapping and fold modeling using Terrestrial Laser Scanning point clouds: application to the Dents-du-Midi limestone massif (Switzerland)

Abstract Geological mapping in vertical rock faces is extremely challenging because of access difficulties and limited possibilities of recognition, localization and measurement of features at large distance with traditional tools. Moreover, vertical areas can be of primary interest since they often display good quality outcrops and relevant geological information. This study focuses on the detailed remote identification of rock types and fold structures using intensity values acquired by Terrestrial Laser Scanning. A correction of the intensity is proposed proportional to the square of the range and to the cosine of the incidence angle. Furthermore, two methods of remote lithological mapping in 3D have been developed using a manual and a semi-automatic approach. Both delivered good results that are consistent with the spatial distribution of rock-types and allowed us to generate an accurate 3D lithological map of Dents-du-Midi massif (Valais, Swiss Alps). The bedding orientation near the hinge of a Km scale fold was measured on LiDAR data in order to define the fold axis. Then, the result was used to build a model of the hinge in 3D.

Assessing rockfall susceptibility in steep and overhanging slopes using three-dimensional analysis of failure mechanisms

Rockfalls strongly influence the evolution of steep rocky landscapes and represent a significant hazard in mountainous areas. Defining the most probable future rockfall source areas is of primary importance for both geomorphological investigations and hazard assessment. Thus, a need exists to understand which areas of a steep cliff are more likely to be affected by a rockfall. An important analytical gap exists between regional rockfall susceptibility studies and block-specific geomechanical calculations. Here we present methods for quantifying rockfall susceptibility at the cliff scale, which is suitable for sub-regional hazard assessment (hundreds to thousands of square meters). Our methods use three-dimensional point clouds acquired by terrestrial laser scanning to quantify the fracture patterns and compute failure mechanisms for planar, wedge, and toppling failures on vertical and overhanging rock walls. As a part of this work, we developed a rockfall susceptibility index for each type of failure mechanism according to the interaction between the discontinuities and the local cliff orientation. The susceptibility for slope parallel exfoliation-type failures, which are generally hard to identify, is partly captured by planar and toppling susceptibility indexes. We tested the methods for detecting the most susceptible rockfall source areas on two famously steep landscapes, Yosemite Valley (California, USA) and the Drus in the Mont-Blanc massif (France). Our rockfall susceptibility models show good correspondence with active rockfall sources. The methods offer new tools for investigating rockfall hazard and improving our understanding of rockfall processes.

Rockfall susceptibility assessment of carbonatic coastal cliffs, Palinuro (Southern Italy)

This short note presents an approach to assess rockfall susceptibility based on terrestrial laser scanner (TLS) point cloud data at the cliff scale. The test area is coastal cliff situated in the southern part of the Campania Region (Centola Municipality, SW Italy), in which a natural arch was formed. Since this coastal area constitutes an important tourist attraction, a large number of people rest on a daily basis beneath the cliffs, increasing considerably the risk associated to rockfalls. The Terrestrial Laser Scanner (TLS) survey of the cliff was realized in june 2015. A structural analysis of the cliff was performed on the point cloud using Coltop 3D software. The different characteristics defining the discontinuity sets were extracted, including orientation, spacing and persistence. The kinematically unstable areas were mapped using a script that computes an index of susceptibility to rockfalls based on the spatial distribution of failure mechanisms. Results show that the kinematically feasible failures are not equally distributed along the cliff. The most important discontinuity set in terms of potential planar failure is K10 (71/097), for the toppling is K1 (60/218). The combination of K10 and K1 has the highest value of susceptibility for wedge failure.