Activity of flow-like landslides on the escarpment cuesta (tree-ring–based study on the eastern margin of the Bohemian Cretaceous Basin).

The escarpments of sub-horizontally deposited rocks represent regional centres of geomorphological activity whose evolution is controlled by the occurrence of different types of slope processes. Surprisingly, historical landslide activity on escarpments of Cretaceous rocks has not yet been studied in detail at the regional level using precise absolute dating methods. In this study, dendrogeomorphic methods including sparse dating with seasonal accuracy were used to determine the activity of flow-like landslides that model the eastern margin of the Bohemian Cretaceous Basin. Geophysical ERT (electrical resistivity tomography) measurements and grain size analysis of the landslide material revealed high saturation of the landslide body with groundwater and a high content of fine-grained fraction, which potentially slows down the infiltration of water into the landslide body, thus moving mainly in its near-surface part. Dendrogeomorphic dating (of 177 Picea abies (L.) Karst. individuals) revealed 7 years of landslide activity in the five landslides studied. The dated movements appear to have a low-magnitude character as indicated by the structure, intensity and duration of the dated growth disturbances. In addition, the dated movements have the character of secondary post-failure movements within up to three generations of older landslide bodies. Dating with seasonal accuracy specified their occurrence to the period July to August. This study represents the first use of dendrogeomorphic methods to characterise landslide movements in a Cretaceous escarpment setting, providing a new perspective on this globally widespread phenomenon. [ABSTRACT FROM AUTHOR]