ABSTRACT

The 8 km Bianco Beach is a wave-dominated high-energy beach composed of sand and gravel. The fluvial gravel output of the Laverde River feeding the Bianco Beach is well defined in terms of petrographic composition, sphericity, and roundness. During the high-energy (storm) stage the entire beach gravel population is transported 200 m offshore perpendicular to the coast. Strong attrition occurs and the amount of less resistant gneiss decreases. The net longshore transport is northward; roundness increases but sphericity remains almost unchanged. During the medium-energy (post-storm) stage, when fair-weather conditions begin to rebuild the beach berm, attrition and rounding are no longer significant. Instead, redistribution and redeposition according to grain size and shape dominates the cross-shore gravel movement with a decrease of sphericity from the offshore to the backshore. Net longshore transport is still northward, sphericity again remaining almost unchanged. During the geologically ineffective low-energy (fair-weather) stage there is some sediment movement along the foreshore, but without any significant gravel exchange between individual beach zones normal to the beach. Such extended fair-weather conditions conserve the sedimentological changes that occurred during higher-energy events. As a result, the proportion of gneiss decreases from 56% to 31% in the net transport direction, whereas the sphericity decreases only from 0.68 to 0.64. Perpendicular to shore the proportion of gneiss decreases seawards from 50% to 37% and the sphericity decreases landward from 0.70 (offshore) to 0.60 (backshore). In contrast, the sphericity frequency distribution of both river / beach and beach start / beach end are almost identical. By retaining its provenance signal, sphericity fails as a meaningful tool for the recognition of geological environments along the Calabrian coast. This inherited sphericity signature of the fluvial output is conserved along the beach and is differentiated only in the cross-shore direction. The overall roundness R increases alongshore by 0.14 (from 0.55 to 0.69) but does not show any trend normal to shore. Continuous and effective rounding along the foreshore during low-energy stages should create much better rounding in this zone than in neighboring zones, which are active only during high-energy stages. The stable cross-shore roundness reflects the "event character" of sediment modification. Only high-energy events move the entire gravel population to yield homogeneous rounding. The results of this study therefore suggest that the Bianco Beach is almost exclusively the product of such high-energy events.