Geomorphological features of the Bratica Valley (Northern Apennines, Italy)

Abstract

The geomorphological survey of the valley of the River Bratica, the main affluent of the River Parma, has been carried out with the aim of improving the knowledge of the geomorphological development of the eastern part of the high Apennines of Parma section. During the survey all the processes responsible for the geomorphic evolution of the valley have been considered, with particular attention to mthose due to the glacial, periglacial and slope processes. The high part of the valley is shaped mainly from the glacial and periglacial processes, active during Middle and Upper Pleistocene. The study has highlighted the landforms due to two distinct glacial phases. Evidence of the most ancient one, called Mt. Navert Phase (Middle Pleistocene), is to be found in glacial deposits containing clasts of Macigno located at Mt. Navert-Pian del Freddo, whilst for the second one, called Parma Valley Phase, corresponding to the Last Glacial Maximum (LGM) of the Alps, in the glacial deposits and moraine ridges surrounding the Mt. Navert-Mt. Quadro area. Equally important is the morphogenesis due to frost action and nivation. Remains of gelifluction deposits (e.g. Lago di Corniglio) and nivation hollows filled by deposits made of different sized clasts (Groppo Fosco-Mt. Quadro) are signalled. The chronology for these landforms and deposits is analogous to that of the glacial phases. The medium and lower part of the valley has been shaped mostly by slope processes with evidence of large complex landslides, sometimes involving entire slopes. Some landslides are active and many others are dormant; the morphologic characteristics of latter suggest that their evolution is very ancient: it began in the periods of climatic deterioration of the Upper Pleistocene and started again during those of the Holocene. In fact the processes active during these periods led to the physicalmechanical weathering of the rocks, thus the instability of the slopes. Today many dormant landslides have become active again, above all during intense and prolonged autumnal rainfall events.