Regional, tree-ring based chronology of landslides in the Outer Western Carpathians

Landslides are a type of mass wasting and denote any downslope movement of soil and rock under the influence of gravity; as such they can represent a dangerous natural hazard process, especially in case that they affect inhabited areas or transport infrastructure. Because the occurrence of landslides is typically favoured by terrain and lithological conditions, the process is frequently concentrated in relatively small, isolated regions exhibiting suitable initial conditions of terrain instability. Extensive regional assessments of landslide activity have been used in the past to uncover common triggers and process patterns, mostly in the aftermath of large, regional disasters. By contrast, however, regional reconstructions of past landslide activity have not been realized with dendrogeomorphic techniques, and with the aim to date past landslide histories over extended time periods and with annual dating precision. This study therefore aims at disentangling landslide dynamics at the regional scale (covering ca. 600 km(2)) by using growth-ring records of trees that grow on active landslides. The studied area of the HostSinsko-vsetinska hornatina Mts. (Central Europe) is well known for its high landslide activity, but has so far been lacking a detailed chronology of past events. To this end, we dated past activity on 26 landslide bodies using tree-ring series from 1322 disturbed trees to reconstruct 327 landslide reactivations during the last century. The reconstructed landslide database allowed correlations between landslide types and their frequencies or occurrence, as well as inferences between selected morphometric parameters with landslide frequency and magnitude. We also observe periods of increased landslide activity (1940s, 1960s, 1980s, and 1990s) and events of regional importance (e.g., 1961, 1985, and 1997), as well as a significant decrease in landsliding during the last two decades. (C) 2018 Elsevier B.V. All rights reserved.