Deep-Seated Gravitational Slope Deformations (DSGSD) often involve complex kinematic behaviors that may vary spatially and temporally. The Alpine area counts several DSGSDs involving volumes of millions of cubic meters. In this paper we present the case study of Spriana landslide, a common example of DSGSD located in the North of Italy. Geological, geophysical and topographic investigations have been combined to develop an accurate physical model of the slope. However, some issues still need to be tackled and the definition of a reliable triggering threshold is yet a challenge. Our work focuses on the importance of the shear surface geometric features for threshold definition. We performed several 3D numerical simulations addressing the definition of groundwater table critical level. We believe our findings may improve the early warning system of Spriana landslide and we think that our approach should be used to address other complex deep seated gravitational slope deformations.
Deep-seated gravitational slope deformations, also known as DSGSD, are common structures that affect mountains chains mainly as a consequence of glacial retirement after the last ice age.The scientific community has widely studied DSGSDs (Bruckl & Parotidis 2005, Guglielmi & Cappa 2010, Gutierrez-Santolalla 2005) focusing on predisposing causes of DSGSDs and on future evolution (Chemenda et al. 2009, Discenza et al. 2011). The Alpine area counts several DSGSDs that threat directly important infrastructures or villages. In Lombardy region there are a number of monitored DSGSDs i.e.: Bindo landslide, Mount Cortafò, Mount Legnoncino, Mount Piazzo, Mount Letè, Mount Ruinon and Spriana landslide. Even if DSGSDs are common in Alps and pose a serious threat to human settlements, evaluating the possibility of a reactivation is still a challenge. It is necessary to better understand predisposing and triggering causes of DSGSDs to improve accuracy in landslide prediction. The starting point for the analysis of these events deals with the definition of an equivalent physical model of the DSGSD. As a matter of fact, the model plays a key role in thresholds assessment useful for an Early Warning System. An effective monitoring system is the unique reliable way to manage landslides of this extension and volume (several millions of cubic meters). Our work focuses on a DSGSD located in the North of Italy. The authors present the case study of Spriana landslide aiming to assess alarm and prealarm thresholds; the process will be shown in each of its steps, focusing on the role of complex shear surfaces.