Paraglacial sedimentation in the Piave Valley (Eastern Alps, Italy): an example of fluvial processes conditioned by glaciation

Abstract

The effects of the last glaciation (Würm) on fluvial processes in an alpine basin (Piave Basin, Eastern Alps) are discussed in this paper. The Piave Basin was completely glaciated during the last glaciation which reached the maximum expansion in the Alps 18,000-20,000 years BP. On the basis of radiometric datings and archaeological data, it can be argued that the deglaciation phase, which began 15,000-16,000 years BP, was relatively rapid. During and after deglaciation a long sedimentation phase (mainly fluvial, but also lacustrine) took place in the Piave valley; this phase ended 8,000-9,000 years BP and was followed by an incision phase with formation of terraces. Sedimentation processes characterised stream channels for a long period of time (about 5,000-6,000 years) after deglaciation. During this period (Late Glacial-Early Holocene), the rate of sediments delivered to streams was much higher than during «normal» conditions (like the present ones), whereas stream flows were likely not so different. It is therefore recognised that the influence of a glaciation on a fluvial system is not restricted to deglaciation period, but it regards a longer period during which a disequilibrium exists between sediment supply to river channels and stream power. It is proposed that the term «paraglacial» could be used in this area and, eventually, in other alpine areas. This term is more suitable than the term «kataglacial» to describe those processes which characterised the transition from a glacial to a non glacial period.