The influence of mylonitic and cataclastic rocks in evaluation of the potential for debris and hyper concentrated flows

摘要

In this study we want to evaluate the large amount of debris by analyzing a typical alpine setting and focusing on the role of mylonitic and cataclastic zones as a potential supply area for debris and hyper concentrated flows. The crystal basement of the Southern Alps, and in particular of the Valtellina area, is dominated by metamorphic rocks, faulted by important regional fault-systems. These fault-systems and the related mylonitic and cataclastic rocks may produce erosion-prone weak rock outcrops responsible for a large amount of debris production and, consequently, localized erosion and sediment contribution to the drainage network. We focus on Val Tartano, which is characterized by the presence of extended mylonitic and cataclastic areas and we analyze these geological structures as potential high-productivity sources contributing to the increase of river solid transport. Characterization of streambed sediment from a grain size and grain shape viewpoint is described, and their dependence upon the eroded geological parent materials is discussed.