debris flow; high-gradient channel; dendrogeomorphology; granulometric analysis; Moravskoslezské Beskydy Mts.

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.