Geology

Signals of global climate change are increasingly evident in the Alps where, in recent years, a growing number of landslides occurred in glacial and periglacial areas. In order to document such a case, a landslide is described and analysed, which affected the SE side of a rocky ridge and the Trajo Glacier below in the Gran Paradiso Massif (NW Italy) during the warm summer of 2017. It was a multiple rockfall of about ½ million m 2 , with vertical drop of %300 m, a runout distance of %900 m, and 17°of travel angle. Prompt field surveys, interpretation of Sentinel-2 satellite images, and an analysis of data from several weather stations, are used to reconstruct the phenomenon and its causes. This study highlights the geological structure of the area (which reflects the morphology and geo-mechanical characteristics of the slope) and the meteorological conditions during the months before the main failure. Moreover it reveals that the landslide was not a single event but developed over time through at least five failures. According to available information, several predisposing factors seem to have played an important such as the degradation of permafrost (probably affecting rock masses at depth), the alternation of freeze-thaw cycles, and the availability of a considerable amount of water from rainfall and snowmelt, infiltrating the rock mass.

Debris flows, and landslides in general, are worldwide catastrophic phenomena. As world population and urbanization grow in magnitude and geographic coverage, the need exists to extend focus, research, and modeling to a continental and global scale. Although debris flow behavior and parameters are local phenomena, sound generalizations can be applied to debris flow susceptibility analyses at larger geographic extents based on these criteria. The focus of this research is to develop a global debris flow susceptibility map by modeling at both a continental scale for all continents and by a single global model and determine whether a global model adequately represents each continent. Probability Density, Conditional Probability, Certainty Factor, Frequency Ratio, and Maximum Entropy statistical models were developed and evaluated for best model performance using fourteen environmental factors generally accepted as the most appropriate debris flow predisposing factors. Global models and...

In a study of debris flow susceptibility on the European continent, an analysis of the impact between known location and a location accuracy offset for 99 debris flows, demonstrates the impact of uncertainty in defining appropriate predisposing factors, and consequent analysis for areas of susceptibility. The dominant predisposing environmental factors, as determined through Maximum Entropy modeling, are presented, and analyzed with respect to the values found at debris flow event points versus a buffered distance of locational uncertainty around each point. Five Maximum Entropy susceptibility models are developed utilizing the original debris flow inventory of points, randomly generated points, and two models utilizing a subset of points with an uncertainty of 5 km, 1 km, and a model utilizing only points with a known location of "exact". The AUCs are 0.891, 0.893, 0.896, 0.921, and 0.93, respectively. The "exact" model, with the highest AUC, is ignored in final analyses due to the small number of points, and localized distribution, and hence susceptibility results likely non-representational of the continent. Each model is analyzed with respect to the AUC, highest contributing factors, factor classes, susceptibility impact, and comparisons of the susceptibility distributions and susceptibility value differences. Based on model comparisons, geographic extent and context of this study, the models utilizing points with a location uncertainty of less than or equal to 5 km best represent debris flow susceptibility of the continent of Europe. A novel representation of the uncertainty is expressed, and included in a final susceptibility map, as an overlay of standard deviation and mean of susceptibility values for the two best models, providing additional insight for subsequent action.

In a study of debris flow susceptibility on the European continent, an analysis of the impact between known location and a location accuracy offset for 99 debris flows demonstrates the impact of uncertainty in defining appropriate predisposing factors and consequent analysis for areas of susceptibility. The dominant predisposing environmental factors, as determined through Maximum Entropy modeling, are presented and analyzed with respect to the values found at debris flow event points versus a buffered distance of locational uncertainty around each point. Maximum Entropy susceptibility models are developed utilizing the original debris flow inventory of points, randomly generated points, and two models utilizing a subset of points with an uncertainty of 5 km, 1 km, and a model utilizing only points with a known location of “exact”. The AUCs are 0.891, 0.893, 0.896, 0.921, and 0.93, respectively. The “exact” model, with the highest AUC, is ignored in final analyses due to the small n...

This paper presents a multidisciplinary approach using modern technologies for the analysis and modelling of the debris flow that occurred at Torrent Rochefort (Aosta Valley—Italy) September 2015. A detailed on-site geological and geomorphological study was performed to highlight the main characteristics of the basin, useful for validating and calibrating dynamic simulations. The total mobilized volume was estimated by comparing a pre-event DTM and a post-event DTM generated from an unmanned aerial vehicle. A digital terrain model comparative analysis provided a quantitative estimation of erodible depths in different sectors of the Rochefort basin. Numerical modelling of the event was performed using the continuum mechanics-based code RASH3D that enabled a simulation of the dynamic debris motion on complex topography. The results demonstrate the importance of a detailed geomorphological study for the validation and calibration of numerical results. Finally, some considerations were ...

Landslides are the most common natural hazard in the Piemonte region (northwestern Italy). This study is focused on shallow landslides caused by the sliding of the surficial detrital-colluvial cover caused by rainfall and characterized by a sudden and fast evolution. This study investigates shallow landslide events compared with variables considered as main predisposing qualitative factors (lithology, pedology and land use) to obtain a zonation of shallow landslide susceptibility in a GIS environment. Additionally, wildfire occurrence is also evaluated as a further predisposing factor for shallow landslide initiation. The resulting susceptibility map shows a strong correlation between the first three variables and shallow landslide occurrence, while it shows a negligible, or very localized, relationship with wildfire occurrence. Through the intersection of the predisposing factors with the landslide data points, a map of homogeneous zones is obtained; each identified zone is charact...

Signals of global climate change are increasingly evident in the Alps where, in recent years, a growing number of landslides occurred in glacial and periglacial areas. In order to document such a case, a landslide is described and analysed, which affected the SE side of a rocky ridge and the Trajo Glacier below in the Gran Paradiso Massif (NW Italy) during the warm summer of 2017. It was a multiple rockfall of about ½ million m 2 , with vertical drop of %300 m, a runout distance of %900 m, and 17°of travel angle. Prompt field surveys, interpretation of Sentinel-2 satellite images, and an analysis of data from several weather stations, are used to reconstruct the phenomenon and its causes. This study highlights the geological structure of the area (which reflects the morphology and geo-mechanical characteristics of the slope) and the meteorological conditions during the months before the main failure. Moreover it reveals that the landslide was not a single event but developed over time through at least five failures. According to available information, several predisposing factors seem to have played an important such as the degradation of permafrost (probably affecting rock masses at depth), the alternation of freeze-thaw cycles, and the availability of a considerable amount of water from rainfall and snowmelt, infiltrating the rock mass.