Late Pleistocene and Holocene fluvial–coastal evolution of an uplifting area: The Tronto River (Central Eastern Italy)

The piedmont area of the River Tronto (Italy) is characterised by Pleistocene and Holocene terraces at progressive elevations a.s.l. After the formation of wide unpaired meander terraces during the Early Holocene, the river created a 20-m-deep gorge into bedrock in its inner part. In mid-valley, the thalweg progressively enlarges and the Late Pleistocene and Holocene terraces converge downstream. A wide alluvial plain was formed during braid-plain aggradation from ca. 4.3 BP, to the end of the 19th century, associated with slope erosion activated by human activities. Since the end of the 20th century, two series of artificial levees were created in order to prevent floods. Due to the reduced dimensions of the artificial river bed, floods still affect large parts of the plain after extreme events. In the coastal sector, during the Early Holocene, a large bay extended approximately 3km inland from the present-day coastline. A barrier beach evolved during the Bronze–Iron Age and, until the Middle Ages, the river mouth entered a large lagoon. Progradation occurred from then until the beginning of the 20th century, when a delta extended up to 500m seaward. During the 20th century, following the creation of the artificial levees and quarrying the beach underwent coastal erosion, and had to be protected by breakwater reefs. The anthropogenic modifications and their effects are among the main factors in the Holocene evolution of the landscape.