Radek TICHAVSKݹ, Karel ŠILHÁN¹ & Radim TOLASZ^2
1University of Ostrava, Department of Physical Geography and Geoecology, Chittussiho 10, Ostrava – Slezská Ostrava, Czech Republic, e-mail: radek.tichavsky@osu.cz (dendroman.cz)
²Czech Hydrometeorological Institute, Na Šabatce 17, Praha 4 – Komořany

ORIGIN, TRIGGERS AND SPATIO-TEMPORAL VARIABILITY OF DEBRIS FLOWS IN HIGH-GRADIENT CHANNELS (A CASE STUDY FROM THE CULMINATION PART OF THE MORAVSKOSLEZSKÉ BESKYDY MTS.; CZECH REPUBLIC)

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High-gradient channels are integral parts of fluvial system in medium-high mountains and concentrate large amount of energy to origin of mass-wasting processes, such as debris flows. This study from the Moravskoslezské Beskydy Mts. tries to give a comprehensive view on debris flow initiation, spatio-temporal variability and potential triggers of these rapid channel processes. Main approach was dendrogeomorphic dating of affected trees supported by granulometric analysis of sedimentary fill and basin morphometric analysis. Geomorphological mapping revealed the most active zones of debris flow occurrence. Accurate tree-ring series dating of 55 samples (both deciduous and coniferous species) with growth disturbances showed 9 different debris flow events during the last 75 years with the highest peak in 1997. Meteorological conditions (extreme daily precipitation or spring melting of snow) allowed origin of debris flows despite the fact that recent sediment source areas occur sporadically. This leads to argument that reactivation of older deposits is the main process of recent debris flows origin. On the other hand, between 1950s and 1980s, when both basins were less covered by trees, there was possibility of higher slope and channel coupling and supplying sediments so debris flows should initiated even in less extreme meteorological conditions.