Mannu tower (Central-western Sardinia, Italy): from petrographic, geomorphological investigations and digital survey to intervention proposal

The Capo Mannu tower rests on a cliff edge in the central-western coast of Sardinia (Italy). It is placed on a 50-60 metres-thick aeolian sequence of Plio-Pleistocene age (Capo Mannu Fm.), that lies above Miocene to Lower Pliocene marine sediments (mainly limestones, sandstones, marly clays). Archival documents attested the decay state of the tower since 1620: “...les torres de Orfano Puddo, Scala Sal y Cabo Maño del Campidano de la ciutat de Oristany ha necessitat deser reparadas en moltes parts...”. Repair interventions were carried out in 1784-1786, and in 1822 by the Towers Administration; the tower was garrisoned until 1846 and then abandoned. The decay of the building materials and of the tower structure is mainly due to the weathering and to the continuous gravitational collapses, triggered by the wave erosion that also produces the cliff retreat. The aim of research is to define: i) petrographic features and chemical-physical degradation of geomaterials; ii) building decay and geomorphological processes through the elaboration of a digital model of the tower and cliff. It will help to better understand the factors that affect the structure decay, and to refer the building materials to the original shape of the ruined tower. The digital survey will be mainly based on drone/UAV photogrammetry, with integration in 3D laser-scanner survey. In its final stage will try to propose possible interventions of consolidation and conservation in such a complex condition.