Marek Křížek

Periglacial Landforms of the Hrubý Jeseník Mountains

This chapter deals with the occurrence, morphology and activity of periglacial landforms in the Hrubý Jesenik Mts. Redistribution of snow during the Last Glacial period , cold climate and the presence of extensive planation surfaces at high elevations have created favourable conditions for the formation and evolution of periglacial landforms, some of which are preserved to this day. Most of these landforms are relict (tors , frost-riven cliffs , cryoplanation terraces , blockfields , sorted polygons and nets, and large solifluction steps ), and only a small part of climatically less demanding periglacial landforms are active (ploughing blocks , earth hummocks , small sorted circles , nivation hollows and small solifluction lobes ). Special attention is paid to patterned ground , which provides information about current and past freeze-thaw effectiveness. Earth hummocks, found at wind-swept sites, on frost-susceptible, fine-grained regoliths, are the most interesting type of patterned ground. Evidence of present-day activity of earth hummocks are distorted soil horizons, vertical and horizontal displacement of clasts, cryoexpulsion features and cracks on crests of earth hummocks, frequent freeze-thaw cycles and long-term freezing. The origin of earth hummocks has been identified as being at the break of the Subboreal /Subatlanti c. The occurrence and activity of earth hummocks, sorted circles and ploughing blocks at several sites above the alpine timberline of the Hrubý Jesenik Mts. allows us to regard these areas as parts of the mountain periglacial zone .

Variability of the Morphometric Characteristics of Valley Networks Caused by Variations in a Scale..

According to their shape, the valley networks are divided into six basic types (Howard 1967; Fairbridge 1968; Demek 1987; Babar 2005; Hugget 2007). Relevance to the given shape tends to be determined only based on the visual similarity to the pattern of the given network shape. The valley networks have a fractal character (Turcotte 1997, 2007a, 2007b; Baas 2002; Mandelbrot 2003) and their analysis is influenced by the scale selection (sensu Bendix 1994). This article indicates the quantitative tools, with assistance of which it is possible to characterize the morphology (shape) of the valley network and determine their variability caused by the scale change. The monitored morphometric characteristics (quantitative tools) are: 1) “number of various order valleys” according to the Gravelius order system; 2) “valley networks’ density”; 3) “bifurcation ratio of various order valleys”; 4) “total lengths of various order valleys”; 5) “total length-order ratio of various order valleys”; 6) “average lengths of various order valleys”; 7) “average length-order ratio of various order valleys”; 8) “fractal dimension of various order valleys”; 9) “relative fractal dimension of various order valleys”; 10) “valley junction angles”; 11) “homogeneity of various order valleys”. These characteristics have been applied to the paradigmatic examples of the schematic valley networks and have been analyzed in three scales. In order to analyze the valley networks, the most suitable are “valley junction angles” and “homogeneity of various order valleys”, i.e. morphometric characteristics resistant to any increase in the scale, “number of various order valleys” and “total lengths of various order valleys”, where the relevant values dropped while increasing the scale, but the normal (Gauss) distribution of values was preserved.

Debris flows in the Hrubý Jeseník Mountains, Bohemian Massif, Czech Republic

ABSTRACT Debris flows in mountainous areas have a deep geomorphic impact on slope dynamics. Their activity corresponds with heavy rainfall events. The estimation of these events depends not only on meteorological prediction but also on the knowledge of their spatial occurrence. As debris flows usually occur in the same paths with different frequencies during the Quaternary period, spatial data are needed to obtain more detailed information about debris flow phenomena. This was the reason for the creation of the presented map of debris flow features in the Hrubý Jeseník Mts. A total of 95 debris flow paths and 47 debris flow accumulations (including lobes or levees) have been mapped in the field. A comprehensive spatial database of debris flow features is shown in the map, which could be helpful for future research of Quaternary geomorphic evolution of the landscape and for forest management and state administrative authorities in future planning.