Tree ring evidence of slope movements preceding catastrophic landslides

Abstract

Catastrophic landslides represent one of the most dangerous natural hazards. Detailed knowledge about the pre-landslide behaviour of the affected slope is crucial for effective modelling of the landslide origin in the future or even for creating an early warning system. As precise retrospective reconstruction of slope movements in the pre-landslide period is very limited, dendrogeomorphic methods can be effective tools for these purposes due to the high sensitivity of trees to slope movements and the spatial aspects of data provided by the position of affected trees. This study presents the results of tree ring-based analysis of slope movements preceding three selected catastrophic landslides of different types in the Outer Western Carpathians (Girova 2010—translational rockslide; Brodska 1997—earthflow; Hluboce 2006—rotational rockslide). Three aspects of pre-landslide slope movements were analysed in detail (frequency, intensity, spatial distribution). In total, 300 tree ring series from 150 trees disturbed by pre-landslide movements were used for these purposes. The Girova landslide was preceded by an increasing frequency and intensity of movements but without any spatial pattern. The Brodska landslide was preceded by a low frequency of low-intensity movements without any temporal trends but with significant clustering several years before the landslide. The Hluboce landslide was preceded by a decreasing frequency of movements with increasing intensity and concentration in the source zone. The character of pre-landslide movements is probably influenced by the presence of old landslide structures on the affected slope and by the mechanism of the movements themselves.