Reconstruction of landslide movements using Digital Elevation Model and Electrical Resistivity Tomography analysis in the Polish Outer Carpathians

Landslides are a major threat to the environment, infrastructure and human activities, especially in mountainous and hilly areas. It is therefore important to accurately identify the mass movements triggering these mechanisms. This paper presents the impacts of lithotectonic conditions on the formation of mass movements on the example of the landslide that is located in the northern part of the Polish Outer Carpathians. In the area of the research, the ratio of the total area of landslides to the surface of the area reaches even 20%. The interpretation of a high resolution Digital Elevation Model (DEM), Electrical Resistivity Tomography (ERT) and fieldwork results allowed for the reconstruction of the landslide movements and dividing them into two areas; the western one, dominated by rotational movement, and the eastern one, featuring rotational and translational movement. It was found that the eastern part is more active now as it probably was also in the past, which might have resulted from the lithotectonic conditioned or from the impact of the flowing waters of the Dunajec River. Moreover, in the eastern part of the landslides, a small-sized ridge (55 m x 25 m) was identified, which shows greater stability in comparison with the colluvium that surrounds it. In order to explain the lower rate of movement of this landform, a morphometric analysis and research using ERT were performed. The geophysical measurements showed that the ridge comprised rock formations of greater resistivity than its surroundings. It is most likely that the only preserved sandstone packet, constituting the original secondary escarpment, became separated from the bedrock due to rotational movement. The presented studies indicate that the landslide was created due to geological and atmospheric conditions. A clear revival of landslide movements took place after significant precipitation events that last occurred in the years 2010 and 2015. The bedrock substrate due to its lithology and tectonics, facilitates these movements. It was found that the landslide studied is a complex entity, characteristic of the Polish Outer Carpathians, that has undergone multiple stages of development. The landslide is active or periodically active and, therefore, must be excluded from the planned development as well as from other forms of human activity.