MODIFICATION OF GRAVEL DURING LONGSHORE TRANSPORT (BIANCO-BEACH, CALABRIA, SOUTHERN ITALY)

The 8 km Bianco Beach Is a wave-dominated high-energy beach composed o f sand and gravel, The fluvial gravel output of the Laverde River feed ing the Bianco Beach is well defined in terms of petrographic composit ion, sphericity, and roundness, During the high-energy (storm) stage t he entire beach gravel population is transported 200 m offshore perpen dicular to the coast, Strong attrition occurs and the amount of less r esistant gneiss decreases, The net longshore transport is northward; r oundness 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 signif icant, Instead, redistribution and redeposition according to grain siz e and shape dominates the cross shore gravel movement with a decrease of sphericity from the offshore to the backshore, Net longshore transp ort is still northward, sphericity again remaining almost unchanged, D uring the geologically ineffective low-energy (fair-weather) stage the re is some sediment movement along the foreshore, but without ally sig nificant gravel exchange between individual beach zones normal to the beach, Such extended fair-weather conditions conserve the sedimentolog ical changes that occurred during higher-energy events, As a result, t he proportion of gneiss decreases from 56% to 31% in the net transport direction, whereas the sphericity decreases only from 0.68 to 0.64, P erpendicular 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 distributi on of both river / beach and beach start / beach end are almost identi cal, By retaining its provenance signal, sphericity fails as a meaning ful tool for the recognition of geological environments along the Cala brian 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, Conti nuous and effective rounding along the foreshore during low energy sta ges should create much better rounding in this zone than in neighborin g zones, which are active only during high-energy stages, The stable c ross-shore roundness reflects the ''event character'' of sediment modi fication, Only high-energy events move the entire gravel population to yield homogeneous rounding, The results of this study therefore sugge st that the Bianco Beach is almost exclusively the product of such hig h-energy events.