Spatio-temporal analysis of a complex landslide in the Northern Apennines (Italy) by means of dendrochronology

Dendrochronology is used to determine the spatial and temporal development of movements in a complex landslide located in the Northern Apennines. The analysis of trees growing on the landslide body enabled us to date their colonisation pattern, which starts from the 1920s and increases mainly after 1950. Since then, sampled trees recorded with growth anomalies the movements involving the landslide body in 1956, 1957, 1982, 1983, 1990, 1995 and 1998. These movements are reactivations of the main landslide that probably occurred in the last decades of the 19th century. In 1980, trees on the upper landslide body were involved in a rock fall due to the expansion of the main scarp. Microsections, cut out from selected tree-ring sequences, allowed seasonal dating of the highlighted movements which mostly occurred in early spring. Meteorological and seismic time series were analyzed in order to relate them with reactivations and to search for correlations and triggering events. The seismic activity, although characterized by low magnitudes, could be able either to trigger the movements (1990) or to destabilize the ground, where rainfalls could have been playing the first role in triggering the reactivation (probably in 1982, 1983 and 1995). The other reactivations seem to be linked either to long-lasting rainfalls or to monthly rainfall peaks mostly following dry periods.