Complex dendrogeomorphic analysis of mass movements in the steep slopes of the Cretaceous canyon

Abstract The steep slopes of incised river canyons may represent a local hot-spot of geomorphic activity in an environment that may not be morphometrically or geologically predisposed to produce significant natural hazards. At the same time, there is often a spatial clustering of different types of hazardous geomorphic processes for whose potential prediction or determination of hazard rates data on their spatio-temporal occurrence in the past is essential. For these purposes, tree-ring-based approaches were used in this study to analyze the behavior of debris flows, landsliding, and rockfall on a Cretaceous canyon slope of the Tichá Orlice river (Czech Republic). Using data from 454 tree-ring series of different coniferous and deciduous tree species, their spatio-temporal behaviour, as well as magnitude-frequency relationships including estimation of potential hydrometeorological triggers, was constructed. In addition, through anatomical analysis of roots stretched over open tension cracks, displacement rate values of the partial slide blocks were calculated. The results highlight the specific character of all the processes studied compared to their nature in the environment typical of their formation (often high mountain ranges). Studied debris flows with a short but very steep path through vertical steps often cause the formation of deep notches in their fans. Slide movements tend to have the character of loosening the slope along vertical fissures, which is reflected in the character of the induced growth disturbances in the trees, but also in the character of the potential triggers. Tree-ring-based research, however, also through the calculation of displacement rates and the construction of magnitude-frequency relationships, has clearly pointed out the potential risk of hazardous reactivations of the studied processes in the Cretaceous canyon environment, and in the future this approach can be used to select optimal positions for the establishment of long-term monitoring.