The dating of bedrock landslide reactivations using dendrogeomorphic techniques: The Mazák landslide, Outer Western Carpathians (Czech Republic)

Landslides predisposed by the anisotropy of flysch bedrock are typical features of mass movements affecting the Outer Western Carpathians. A dendrogeomorphic investigation involving an extensive dendrometric (n = 1680) survey and tree-ring analysis of 176 Norway spruce trees (Picea abies (L.) Karst.) was used to reconstruct the spatial and temporal activity of the Mazák landslide, situated in the highest part of the Czech Outer Western Carpathians. As revealed by geomorphic analysis and electrical resistivity tomography, the landslide is a translational medium-depth (< 30 m) bedrock feature originating at the intersection of inclined bedding planes with diagonal (NW–NNW striking) and longitudinal (NE striking) sets of joints and faults. Dendrometric data supported by correlogram analysis suggest the coincidence of landslide reactivations with the presence of diagonal pervasive bedrock fractures. A tree-ring analysis shows nine major landslide years (1929, 1940, 1949, 1960, 1972, 1980, 1985, 1997, and 2000) accompanied by six additional years with minor reactivations (1933, 1945, 1955, 1958, 1977, and 1996) during the past hundred years (1912–2011). Major growth reactions to landslide movements in the study site were demonstrated by the occurrence of reaction (compression) wood and by the abrupt suppression of growth. An analysis of climatological data shows that the most likely meteorological triggers of the landslide reactivations are summer precipitation (especially heavy rainfall events in July and August with total rainfall of > 200–300 mm per 10 days).

► We present landslide in the culmination part of the Moravskoslezské Beskydy Mts.
► Analysis of landslide activity was based on dendrogeomorphic and dendrometric methods.
► Active landslide zones correspond with position of fault systems.
► Landslide events occur mainly in years with summer heavy rainfalls.