Sediment texture in rock avalanche deposits. Insights from field and experimental observations

Sedimentary structures within rock avalanche deposits have gained increasing attention in recent years, since they may provide useful information about the dynamics of such energetic events. This work then is aimed at better defining the physical processes arising during the propagation, paying particular attention to the kinetic sieving mechanism, and strengthening the assumption (widely diffused in the literature) that such a process does not occur for similar events. Specifically, after the examination of two rock avalanche deposits in Central Italy, where cuts through the fragmented deposits are accessible and illustrative of the sediment texture, a series of laboratory flume tests have been performed in order to investigate in detail the flowing process. A simplified physical model for granular agitation has been then introduced to explain how and why kinetic sieving may occur at the laboratory scale and, in the case of natural granular flows of reduced size, also at the field scale.