Formation, characterization, and modeling of the Val Pola rock-avalanche dam (Italy)

Landslide dams can be originated by very different phenomena, each characterized by specific types of movement, which control the final characteristics of the material. We present the case study of the Val Pola landslide dam (Central Italian Alps, Lombardy), formed in 1987 by al large rock avalanche. We describe the main landslide features as well as those of its accumulation. Data from laboratory and in situ tests performed on the landslide deposits are reported and discussed. The collected data are used to describe the internal structure of the accumulation, the behaviour of the landslide dam during the lake infilling and the overtopping phase. These data are fundamental to interpret the mechanisms of put in place of the accumulation and the theories proposed to explain long runout of rock avalanches. We compare the grain size distributions of the deposits and the physical-mechanical properties from different landslide sectors. We stress the relevance of a detailed characterization of the internal structure of landslide dams to perform correct seepage modelling and to perform reliable predictions of landslide dam stability and breaching (geometry, water and sediment discharge, duration). Point-like characterization, often controlled by local conditions and presence of small outcrops, can be misleading both in terms of the evaluation of the stability of the dam and in the understanding of the processes. We used several published relationships and approaches for the assessment of the peak discharge, breaching time and geometry. We confirm the large variability of the results and the difficulties in using collected data for reliable predictions.