Seasonal determination of mass movement occurrence by means of dendrochronology and wood anatomy: examples from Italian case studies

Abstract

Dendrochronology has often been used to determine the spatio-temporal evolution of mass movements, allowing the annual dating of events. In this study we present the possibility of defining the seasonal occurrence of events by using dendroanatomical techniques. For these techniques we need to determine the trees radial growth period. This was done by cutting and analysing thin sections from selected tree ring sequences. The anatomical structure of normally growing tree-rings was compared with the structure of tree-rings showing growth anomalies. This allowed a setting of the occurrence of growth anomalies within the growing season. The mass movements analysed are located both in the Alps and in the Apennines. Reactivations characterized the Apenninic landslides mostly during the dormant season, rarely during spring or summer. On the contrary, debris flows, analysed in the Italian Maritime Alps, occurred mostly in the late spring-early summer period. The determination of mass movement occurrence with a seasonal definition enabled us to restrict the time span in order to analyse correlation between the events and their triggering causes.