Pavel Mentlik

Abstract:

Abstract: A detailed geomorphological map of the surroundings of Prasilske Lake, Bohemian Forest, Czech Republic is presented. A layer of elementary forms (segments of relief nearing constant values of fundamental morphometric variables) holistically covering the whole mapped area was used as a base for mapping. Elementary forms were delineated by: i) analysis of contour lines and a DEM; ii) verification on orthophotomaps and iii) field mapping, where boundaries of each form were verified (195 elementary forms were mapped). Elementary forms were grouped according to their genesis to form geomorphologically homogenous landforms. The geomorphological map covering a 955 ha previously glaciated area is focused on morphogenesis and morphochronology. Additional maps at 1:20,000 provide information about geological characteristics and their interrelations with the main relief features. A map of the scientific reliability of landform origins presents the degrees of uncertainty in geomorphological knowledge. The mapping of elementary forms and the map of scientific reliability provide a holistic view of the mapped area (fundamental for comprehensive analysis of relief), a base for systematization of the relief and a platform for the evaluation and planning of research.

Abstract: Although the Bohemian Forest is generally considered to be geomorphologically a rather stable region, there are localities which bear proof of a surprisingly high intensity of recent and even present day processes. A multidisciplinary methodology based on the analysis of slope systems was used for researching the present and past dynamics of two hillslopes. Using the results of direct dilatometric monitoring (the slow creep of rock blocks reached a maximum of 1 mm year-1), GPS field mapping, sedimentology, geodetic measurements and DEM analyses, several common rules have been observed for the behaviour of two model localities and a likely polycyclic development established, with recurrence of mass-wasting cycles related to material supply thresholds. Radiometric dating of debris flow activity showed that the cycles span approximately 4000 years. In this area of rather stable bedrock conditions, at least two factors that decrease slope stability need to act together to activate slope processes: i.e. a favourable structural predisposition (dip of major joint or bedding planes) and an increase in relief through either glaciation or river incision. Copyright © 2010 John Wiley & Sons, Ltd.

Abstract: Comprehensive geomorphological and sedimentological analyses confirmed three phases of Würm glaciation in the surroundings of Prášilské Lake and Stará Jímka, in the Bohemian Forest (Šumava Mountains). Glaciations were affected by a steep east-facing slope, by plateaus on the adjacent ridges and by local geological conditions. A small valley glacier (about 2 km long and 50 m thick) occurred during the first phase. In the second phase, a glacier-rock glacier developed, probably based on remnants of the valley glacier. During the last phase glacial activity was divided into Stará Jímka and the stepped cirque of Prášilské Lake. A further shallow ( 3 m deep) lake in Stará Jímka was dammed by slope movements after deglaciation ( 14 cal. ka BP) and survived until 4 cal. ka BP. The Late Pleistocene chronology of the Bohemian Forest seems to be related more closely to the Alps than to northern Europe. In the mid-mountains of central Europe, Pleistocene glaciation decrease significantly eastward, because of increasing continentality. The presence of plateaus (deflation areas), around 1300 m altitude, across the approach of westerly winds was important for the development of glaciers in the Bohemian Forest. The termination of glaciation before the Younger Dryas is specific to the Bohemian Forest in comparison with the Vosges and Krkonoše Mountains.