Anna Bucała

Abstract Heavy downpours and flash floods accelerate the denudation of slopes, as well as erosion, and hence accumulation in the bottoms of valleys (Słupik, 1981; Starkel, 1996; Gil, 1998). However, the geomorphological impact depends less on the amount and duration of falls of rain, and more on intensity and spatial extent. The intensity of mass movements and floods also depends on relief, the type and thickness of soil, the lithology and tectonic history of rocks, which together determine infiltration rates and runoff. An important role in triggering mass movements is also played by human activity (land use, terracing and the undercutting of slopes). This paper presents the role of short-duration downpours occurring in the July of 1997 and 2008 where the shaping of the Jaszcze and Jamne valleys in the Gorce Mountains is concerned. The narrow valley of the Jaszcze has very steep slopes and is covered by dense patches of forest. In contrast, the Jamne Valley with its predominantly gentle slopes has been largely deforested. At higher elevations, the Jaszcze catchment has a prevalence of meadows and pastures that contrasts with the dominant arable land lower down. The Jamne catchment in turn has meadows and pastures of its own, plus arable fields reaching altitudes of 1100 m a.s.l. (Obrębska-Starklowa, 1970). Following the rainfall of July 1997, it proved possible to register 85 new superficial landslides on air photos (55 in the Jaszcze Valley and 30 in the Jamne Valley), these covering a total area of c. 29,700 m2. Among dominant forms were slumps and mudflows of loamy-sandy regolith, created mainly on steep, grass-covered slopes (≥20°), on the edges of field terraces and on the colluvium of old landslides. A flood of 23 July 2008 was also connected with a heavy downpour, daily rainfall that day reaching 76.3 mm at the river outlet. The highest level in the Jaszcze and Jamne was noted at about 17.00. The most marked changes characterised the Jamne channel, this reflecting its more limited forest cover and the higher density of the river network. Lateral erosion prevailed over downcutting, causing the reactivation of old undercuts and the development of new ones, the height reaching 3.5 m. Boulders up to 25 cm in size were transported, and the deposition of debris followed. Older gravel bars were cut and new ones built up. Only a few small earth slumps appeared on the slopes, and these were never in forest. A map showing the potential susceptibility of the Jaszcze and Jamne catchments was prepared on the basis of field data and a statistical analysis, using the landslide index method (Van Westen, 1994). While the greatest geomorphological effects of rainfall are to be noted in stream channels, the transformation of slopes by mass movements is less remarkable. However superficial landslides are characteristic of deforested slopes covered by a thin loamy regolith over flysch sandstones and shales. GIS analysis and field observations make it clear that the geological structure deeper down does not play an important role in triggering of superficial landslides.

Keywords: opady nawalne, ruchy osuwiskowe, procesy korytowe, Gorce

Anna Bucała [abucala@zg.pan.krakow.pl], Institute of Geography and Spatial Organization Polish Academy of Sciences, Św. Jana 22, 31-018 Kraków, Poland

Citation

APA: Bucała, A. (2009). Rola opadów nawalnych w kształtowaniu stoków i koryt w Gorcach na przykładzie zlewni potoków Jaszcze i Jamne. Przegląd Geograficzny, 81(3), 399-418. https://doi.org/10.7163/PrzG.2009.3.5
MLA: Bucała, Anna. "Rola opadów nawalnych w kształtowaniu stoków i koryt w Gorcach na przykładzie zlewni potoków Jaszcze i Jamne". Przegląd Geograficzny, vol. 81, no. 3, 2009, pp. 399-418. https://doi.org/10.7163/PrzG.2009.3.5
Chicago: Bucała, Anna. "Rola opadów nawalnych w kształtowaniu stoków i koryt w Gorcach na przykładzie zlewni potoków Jaszcze i Jamne". Przegląd Geograficzny 81, no. 3 (2009): 399-418. https://doi.org/10.7163/PrzG.2009.3.5
Harvard: Bucała, A. 2009. "Rola opadów nawalnych w kształtowaniu stoków i koryt w Gorcach na przykładzie zlewni potoków Jaszcze i Jamne". Przegląd Geograficzny, vol. 81, no. 3, pp. 399-418. https://doi.org/10.7163/PrzG.2009.3.5