Geomorphological and geo-environmental features of the Graveglia Valley (Ligurian apennines, Italy)

This paper presents a review of geomorphological and geo-environmental studies conducted in the Graveglia Valley, where Bracco-Val Graveglia Unit and Mt. Gottero Unit formations outcrops appear. The Bracco-Val Graveglia Unit consists of serpentinites and peridotites, gabbros, ophiolitic breccias, basalts, cherts, limestones and clayey shales. The Mt. Gottero Unit is made up of clayey-arenaceous schists, slates, shales with marly-clayey layers, sandstones and clayey shales. The geomorphological layout is conditioned by the geological and structural characteristics of the valley. The principal tectonic trends, which consist of two orthogonal systems, one trending N-S to NW-SE and the other NE-SW, have determined the drainage pattern and are responsible for the formation of some deep-seated gravitational slope deformation. Investigations carried out on the gravitational processes affecting the slopes have led to the mapping of landslides involving monolithological deposits and mixed lithologies, both deposited by rockfalls and sliding. For the most part, these deposits are present in the upper part of the valley. Along Graveglia Valley, which is marked by frequent meanders, terraced alluvial deposits prevail from the outlet to as far as Frisolino. The upper part is instead characterized by rock erosion. Level surface areas attributable to fluvial terraces (sometimes with ancient alluvial deposits) are present at higher altitudes on the slopes, while alluvial cones are observable at the confluence of the tributaries flowing into Graveglia stream. As concerns underground water, numerous springs exist throughout the entire basin. They constitute an important water resource. Karstic modelling has developed in the extensive outcrops of limestones present in the upper valley. Microforms of corrosion and dolines represent some of the epigenic forms, among which the Pian di Oneto landform of tectonic-karstic origin is the most imposing of all. As for hypogenic forms, there are about thirty caves, both active and fossil. Landforms attributable to anthropic activity are numerous and mainly distributed in areas with rocks of oceanic sequence. The most important ones are present in mining sites worked for manganese, iron and copper sulfides. Numerous stone quarries are found one after another in the limestones between Frisolino and Arzeno. The blocks extracted in these quarries are used for breakwaters and the crushed rock is used for construction purposes. In the past, quarries had also been opened in the serpentinites and in the basalts. Lastly, environmental and geotourism points of interest have been indicated on a geomorphological map presented here. These points are related to the geomineral aspects of the areas, as represented above all by the Mining Museum of Gambatesa, as well as to geological-geomorphological aspects, such as the quarry fronts, the gorges and meanders, the agricultural terraces and dry stone structures.