Modificazioni morfologiche oloceniche nelle piane alluvionali marchigiane: alcuni esempi nei fiumi Misa, Cesano e Musone

Holocene geomorphological variations in the marchean alluvial plains: some examples in the Misa, Cesanoso and Musone Rivers

Abstract

The Holocene evolution of the middle part of the Misa and Cesano valleys is characterized by the formation of various minor terraces which could be grouped in at least 5 main phases A meander course was evolving in the first two phases, between Early Holocene and Roman times. A third phase reveals a progressive transition from a meander to a braided river which took place between the Roman times and the end of the l9th century. At the end of the 1940′s or 50′s the penultimate terraces ceased to be modelled, and the progressive incision of the thalweg, which is still going on (phase 5), started. In the upper Mesone river the post glacial down cutting has always been connected to a meander course up to the plain located few meters above the present thalweg. The important post-roman aggradational phase does not seem to be derived from the degradation of the mountain slopes but mainly from that of the periadriatic basin pedemontan and hilly slopes. A first phase of aggradation is documented at the mouth of the Misa river in pre-roman times to which is related the formation of a sandy-gravelly shoreline parallel to the coastal cliff. Landward, coastal swamps, abandoned channels, and small islands were created at the top of which Senigallia was founded in the third century B.C. The aggradation was considerably accelerated after the l5th century. The variation from a meander to a braided river and the associated general aggradation of the Marches rivers is attributed to slope erosion following the deforestation for the development of agricoltural and grazing activities, first during the Bronze-Iron age and later, and to a greater extent, at the Renaissance. To this process the progressive change of the coastal morphology is connected, characterized by active cliffs alternating with small intravalley bays in pre-Roman times. Progressively the coastal beach which at present almost everywhere borders the Marches coasts was to develop.