LANDSLIDES: A NEGLECTED ENVIRONMENTAL PROXY ARCHIVE?

To answer the questions concerning how and why climate has varied on different time-scales over the Quaternary, the key is to improve the documentation and understanding of natural variability for periods extending back beyond the instrumental record. Knowledge of past climate changes has to be gained from well-calibrated proxy data derived from natural archives. In an ideal situation such archives provide accurate records of climate history, can be dated with annual precision on a calendar year time-scale and can be correlated through time. Actually, no single archive encompasses such properties and information from different sources are to be merged in paleoclimatic reconstructions. Among these sources, however, landslides and in particular the temporal concentrations of instability events have been by now neglected, though they could improve significantly the insight of the environmental context as a whole. It should not be omitted that, even when the geomorphological evolution of a slope can be described by way of surveys, radiometric dating, cross-sections etc., its entire history may not be feasible and there can still be lacks in space and time due to the inherent mechanisms of landslide processes and to their episodic behaviour. Nevertheless, if landslides are regarded as proxy, these constraints can be overcome starting from the assessment of a site susceptibility to instability and the evaluation of the paleoclimatic significance of the landslides considered. Actually, the variation of stability conditions through time depends on the slope response to different potential causes, both external, such as climatic and seismic ones, and internal, such as geological, structural, hydrogeological etc. When climate is considered to be the main cause of instability, concentrations of events become significant in a paleoclimatic perspective, if a sufficient number of landslides have been recorded. Therefore, though the records of landslide activity are not likely to be considered as comprehensive proxy archives sensu stricto, still they can give a significant contribution to the establishment of a paleoclimatic multi-proxy database when the environmental context is analysed with a multidisciplinary approach.