Tree ring based estimation of landslide block displacement: Evaluation of a new experimental approach

The mechanisms and velocities of landslide movements are important information for assessing hazards associated with landslides. This contribution introduces a new approach in reconstructing the past rate of landslide displacement using dendrogeomorphic methods. The principle of this method is based on the analysis of exposed roots in tension cracks or scarps of active landslides. The identification and dating of anatomical changes in root ring series in various root segments, induced by gradual root exposure due to crack spreading, enable the estimation of the rate of root exposure and the calculation of the displacement rate of landslide blocks. We analysed anatomical reactions of 87 root cross sections in tension cracks of an active landslide the Moravskoslezske Beskydy Mts. in the Outer Western Carpathians. Microscopical analysis of microcuts from cross sections showed the reduction in the earlywood vessel sizes, indicating the year of root exposure. We identified 17 years of exposure between 1997 and 2015. We calculated the individual displacement rates of the landslide expressed as the segment rate between the two adjacent samples of tension crack spreading and the mean spreading rate for all roots crossing one tension crack. The average total spreading rate for each tension crack was 3.2 cm year−1, with a maximum of 4.3 cm year−1 and a minimum of 1.7 cm year−1. Although this new approach has some uncertainties and limitations, it remains a low-cost technique that allows us to reconstruct the minimal past rate of landslide displacement without the need of long-term monitoring.