Morphodynamics of steep mountain channels

Steep mountain channels are intrinsically transitional systems, in that they connect water, sediment, and wood fluxes from hillslopes, chiefly dominated by colluvial processes, to highorder streams, in which fluvial transport prevails. Owing to the variety of colluvial–alluvial interactions, the transient forcing of tectonic activity and Pleistocene glaciations, in conjunction with ongoing atmospheric temperature rise and increasing anthropogenic impacts, mountain channels exhibit complex, largely unknown hydro-geomorphic dynamics. An improved understanding of these systems is needed for addressing fundamental scientific issues such as hillslope-channel coupling mechanisms and landscape evolution, as much as for solving more practical problems, including sediment management and the prevention/mitigation of flood- and debris flowinduced disasters. This special issue encompasses a number of studies addressing the morphodynamics of steep mountain channels while focusing on different geomorphic processes and spatial/temporal scales, and across a variety of physiographic settings, all testifying to the dynamic and diverse nature of such channel typologies. The wide range of techniques presented here, exemplifies how direct and surrogate bedload measurements, flume experiments, sedimentology and dendrochronology can all help shed some new light on the hydrogeomorphic functioning of steep channels.