Criteria for a preliminary assessment of landslide dams evolution

Landslide dams are common phenomena world-wide and, in this paper, the results of the main inventories from bibliographic review have been examined in order to better define those variables that control their evolution. Not all landslides are capable of blocking a river channel, but only those ones that can carry a great amount of material characterized by velocities ranging between high (>5 m/s) to moderate (>13 m/month). Of course geotechnical properties of the material forming landslide dams exert a control on their stability. In this paper results obtained by a classification of dam debris depending on parent rocks in which landslide developed, are presented. The last part of the paper shows improvements to the theory, proposed by previous authors, that landslide dam evolution can be forecasted by defining geomorphic indexes that result from the combination of variables identifying both dam and dammed river. In particular the dimensionless blockage index (Ib’), expressed as Ib’=Log(Vd/A×Hd), based on an analysis that took into account 83 episodes, resulted a useful tool to make accurate predictions.