The Structural Control of a Landslide Development and Functioning of a Lake Geoecosystem in the Catchment Area of the Hucianka Stream (The Outer Carpathians, Beskid Niski)

The landslide in Huta Polańska (Beskid Niski/Lower Beskids) is an example of a particular lake geoecosystem. The largest inter-colluvial depression forms a lake basin constantly filled with water, with a natural outflow in the form of a watercourse. Three drainless sink-holes constituting places of periodical accumulation of water and organic-mineral sediments were localized within the landslide. The direction of the landslide movement and its wedge-like shape are determined primarily by the fault surface located in its south-western part. It also forces the linear course of the streams and the cascade location of depressions between colluvial ramparts, seasonally or permanently filled with water. The inventory of minor tectonic structures and the morphotectonic analysis indicate tectonic conditions of this landslide lake geoecosystem. The structures located within the fault surfaces are indicative of shear stresses and their orientation determines the direction of rock movement (Zuchiewicz, 1997a; Szczęsny, 2003). The morphological analysis and correlation of landslide forms indicate the combined rotational-translational motion. It was ended by mud and debris flow which divided the valley longitudinal axis and damming the waters of the Hucianka stream. The result is a landslide dam lake, whose effects are visible within the floodplain above the former landslide dam. In order to formulate the final conclusions regarding the morphotectonic analysis and the slope transformation phases, laser scanning photos were also used.