In this work we describe the role of landslide processes in shaping river channels and the development of valley floors in 3 rd and 4 th order catchments in the Polish Flysch Carpathians. The main focus of the study was on the contact zone between the landslide system and the river channel, where it has been shown that 30.2% of the length of the river network are affected by landslides. Research shows that 93% of landslides have some form of contact with the river system. Research further shows that the most common contact types in the study are point and area types according to the Korup classification. The most common impacts of landslides on the river channel are riparian and partial occlusion types. Landslides very often cause complete or partial displacement of the river channel, which frequently leads to the blockage of flow, which in turn creates landslide lakes, followed by accumulation zones. The effect of such events is the transformation of the longitudinal profile of the river and the intensification of erosive processes in the contact zone and downstream. Increased activity of erosive processes can lead to the activation of landslide processes, including on the opposite slope.

<p>The research is focused on the development of landslide slopes in areas with mixed agricultural and built-up land use in the middle mountain region. The multi-stage studies of the development of landslide slopes were carried out in the 20-year period after na extreme 1997 hydrometeorological event in Beskid Wyspowy Mountains, Polish Flysch Carpathians.</p><p>Landslides occupy 30-70% of slopes in the Flysch Carpathians. Meanwhile, this region has high population density (approx. 130 people per km<sup>2</sup>), which combined with medium inclination of slopes encourages people for settlement and agricultural land-use on landslide slopes. Development of slopes in the Flysch Carpathians occurs most often during extreme hydrometeorological events. One of the most significant events took place in 1997 and it was unique one in terms of both the rainfall total and its intensity. After this event approximately 20,000 landslides were created or reactivated in the Polish Carpathians.</p><p>Six areas in the immediate vicinity of the Łososina River and its tributaries were selected for the study. All areas were transformed by landslides during the 1997 event. The degree of activation of landslides was determined on the basis of field studies carried out after the extreme event in 1997 and the analysis of DTM and orthophotos (1997-2019). A number of relief parameters of activated landslides were analyzed in detail, including: slope, density of drainage network, shape (W/D), type of landslide.</p><p>In five studied areas older landslides were present, covering up to 65% of the area. In one of the studied slope no landslides older than 1997 were detected. Most of landslides that occurred in 1997 occurred within the older landslide forms. As a result, the total area of the slopes affected by "new" landslides increased by only 1.0-1.7% of the studied slopes’ area. The rejuvenated landslides covered 8 to 26% of the area of landslides existing before 1997. Principal landslide activity was the formation of numerous secondary scarps, fissures and a fresh accumulation zones of colluvia. Subsequent development of the landslide slopes during the 1997-2017 period was investigated. Extreme precipitation events occurring during that period, especially in 1998, 2001, 2010, 2014, were analyzed in terms of their efficiency in transformation of the studied landslides.</p><p>The changes in land use in activated parts of landslides were also analyzed. It was found that there was a significant increase in forest area of 13-52% in activated parts of the landslides in 2017 compared to 1997. As a result a complex land use mosaic developed in the study area with forest patches and different agricultural areas (pastures, orchards, arable lands and abandoned fields).</p>

<div> <p>The study is focused on a multi-staged development of slopes affected by landslides in Beskid Wyspowy Mountains, Polish Flysch Carpathians. The role of extreme 1997 hydro-meteorological event as well as successive events in years 1998-2017 in landslide triggering was particularly taken into account.   </p> </div><div> <p>The flysch Carpathians are characterized by large percentage of an area affected by landslides. Landslides occupy 30-70% of slopes in this area. Meanwhile, this region has high population density (approx. 130 people per km2), which combined with low inclination of slopes encourages people for settlement and agricultural land-use on slopes, including landslide slopes.  </p> </div><div> <p>Development of slopes in flysch Carpathians is currently progressing mainly during extreme hydro-meteorological events. One of the most significant events took place in 1997 and it was unique one in terms of both the rainfall total and its intensity. After this event approximately 20,000 landslides were created or reactivated in the Polish Carpathians.  </p> </div><div> <p>Six slope sections ranging from the foot to the top of the ridge were selected for the research. All these sections were transformed by landslides during the 1997 event. They are all located in the Beskid Wyspowy Mts., which is one of the regions most affected by landslides in Polish Flysch Carpathians in 1997.  </p> </div><div> <p>The degree of activation of landslide slopes in 1997 and thereafter was defined based on field research and the analysis of DTM and orthophotomaps. A number of parameters of the relief of activated landslides were analyzed in detail, including: their slope, network of drainage. Later these parameters were compared to the relief parameters in inactivated parts of landslides. </p> </div><div> <p>In one of the studied slope sections no landslides older than 1997 were detected. In other studied slope sections older landslides were present, covering up to 65% of the section’s area. The rejuvenation of landslides covered from 8 to 26% of the area of landslides existing before 1997. Main landslide activity was the formation of numerous secondary scarps, fissures and a fresh accumulation zones of colluvia. Most of landslides that occurred in 1997 occurred within the older landslide forms. As a result, the total area of the slopes affected by landslides increased by only 1.0-1.7% of the studied slopes’ area.  </p> </div><div> <p>The further development of the landslide slopes in the period 1997-2017 was investigated. Precipitation events occurring during that period, especially in 1998, 2001, 2010 2014, were analyzed in terms of their efficiency in transformation of the studied landslides. The changes in land use in activated parts of landslides were also analyzed. It was found that there was a significant increase in forest cover of 13-52% in activated parts of the landslides in 2017 compared to 1997. An increase in the diversity of the relief of landslide slopes and a greater mosaic of land use, especially a decrease in agricultural land for the benefit of the forest were found.</p> </div>