Assessment of Landslide Activity and Hazard Recorded in Tree Rings—Examples from the High-Risk Vernazza Catchment (Liguria, Italy)

In the Vernazza catchment located in Italian Liguria, we studied the activity and hazard of two deep-seated landslides using tree rings. Knowledge of the deep-seated landslide movements in terms of their temporal activation is still scarce in the Vernazza catchment, as well as in similar catchments. To determine the hazard of the studied landslides, we compared the landslide activity for landslides under study with landslides from Poland that activated in 2010. Within the two studied Italian landslides, increased landslide activity occurred at similar times, but the dominant episodes occurred in different years. It means that the information on landslide activity and hazard should be generalised with caution, even within a single catchment. The studied deep-seated landslide activity was significantly higher after the landslide catastrophe in 2011, when many shallow landslides were activated in the studied catchment. The increase in landslide activity in 2011 was accompanied by a substantial transformation of the catchment's relief. These changes may have resulted in a loss of stability of deep-seated landslides. The landslide activity recorded by trees did not show an increase, unlike what was reported for the Polish landslides. This indicates that there is no high risk of sudden triggering of the studied landslides.