STRUCTURAL CONTEXT OF LANDSLIDE DEVELOPMENT IN POLISH OUTER CARPATHIANS. CASE STUDY FROM UPPER VISTULA AND OCHOTNICA VALLEYS

The aim of the presented research is to analyse the relation between the development of landslides and the geological structure in the Polish part of the Outer Carpathians fold and thrust belt. Two groups of factors, i.e. passive and active, influenced the evolution of landslides. The active factors are the external and internal elements connected with the climate, physical processes and human activities. They had a direct effect on the occurrence and distribution of landslides. The passive factors include geological and morphological conditions such as the lithology, bedding, folds, faults and fractures, slope dip and aspects. The passive factors, which are the focus of our work, have determined places where the active factors are likely to appear resulting in a high possibility of landslide occurrence. The Polish Outer Carpathian fold and thrust belt is a region built of sandstone-shale flysch deposits of turbidite origin. Our research was conducted in two regions – the Upper Vistula and the Ochotnica valleys. Landslides were mapped as part of preparation of the Landslide Counteracting System. The geological research included field observations and measurements focused on the lithology and structural elements as well as analysis of digital elevation model based on LIDAR data and aerial radar photography. In order to compare the landslide distribution with the geological factors, we used two techniques: (1) statistical analyses based on stereographic projection using Schmidt net and (2) building a 3D geological model in order to calculate the distribution of consequence ratio, geological formations and density of faults. Both methods showed and confirmed that the mechanical characteristics of flysch rocks, especially thickness of shale and sandstone beds, relation between bedding and slope direction, density and orientation of the joint network as well as the complex tectonic structure had a huge impact on the development of mass movements.