Specifics of slope movements on slopes with contrasting structural conditions: Evidence from tree-ring records

Abstract

The geological structure of a slope is one of the key factors that drives the development of landslide types. Various landslide types, although occurring in the same locality, can result in different spatio-temporal dynamics of their movements. Moreover, the presence of shallow creep movements on such slopes can modify the effect of slide movements and possibly cause the false impression of landslide activity. The nonstandard combination of detailed tree-ring-based (dendrogeomorphic) approaches involving the careful assessment of growth disturbance properties (the duration, intensity, mutual ratio of different disturbances), the statistical testing of the spatial pattern of disturbed trees, the analysis of possible extreme precipitation triggers, and geophysical sounding was used in this study in an attempt to distinguish creep and slide movements and assess the general slope movement activity on slopes with contrasting geological structures. Data from 1032 tree-ring series of 516 disturbed individuals of common spruce (Picea abies (L.) Karst.) enabled the reconstruction of 13 slope movements on all three studied sites (3, 7, and 3) for the last approximately 70 years. Although some indices correspond with the general assumption of a specific landslide type to the structure of induced growth disturbances (e.g., an increased ratio of reaction wood on rotational landslides), the advanced dendrogeomorphic approach used suggests that not all dated events are of slide origin and that creep movements significantly modify the effect of original slide movement on tree growth. Some dated events are probably the result of only creep movements themselves. Thus, the present study critically assesses results of the dendrogeomorphic dating of various landslides, presents contrasting behavior of slope movements on slopes with contrasting geological structures, and recommends the use of more advanced tree-ring-based approaches for more effective dendrogeomorphic research of landslides.