Geomorphological hazard in the Tharros archaeological area (Western Sardinia, Italy)

The Special Project "Safeguard of Cultural Heritage" of the Italian National Research Council is the main Italian scientific project dealing with the conservation and protection of cultural wealth and it is carried out in close co-operation with the Public Administration. The Earth Sciences Department Of the University of Florence is responsible for the assessment of geomorphological hazard which affect archaeological sites and in this paper the results from the main case studies arc presented: the Phoenician-Punic town of Tharros in Sardinia. Since the 50's several archaeological campaigns in the western Sardinia have brought to light the ruins of Tharros in the Capo Son Marco peninsula. According to the archaeological evidence the peninsula was sporadically occupied in the Nuragic period (9(th) century, BC), but the first stable harbour can be referred to the period of Phoenician colonisation (730 -770 BC). In the 6(th) century BC Tharros was subjected to Carthaginian rule and acquired a certain importance as strategic centre for the control of the trade routes in the Mediterranean. The scarce know,ledge available on the long period of Phoenician-Punic administration shows that Tharros was a vital centre in the coastal fortification system set up in the Mediterranean. The town, conquered by the Romans shortly after the First Punic War (238 BC), had alternating fortunes under colonial rule within the Roman Empire. The decline of the Empire was followed by, Vandalic and Byzantine rule until the town was definitively abandoned in the 9(th) century AD, probably because of its exposure to Saracen forays. The visible remains of these sixteen centuries of history, are various and complex because of the inevitable super-imposition and interference of the various conceptions of urban design. The elements of major interest are: the urban nucleus with its temples, civil buildings, thermal baths, the Roman road network; the Phoenician sacrifice area of Tofet; the two necropolises of Capo San Marco and San Giovanni, located respectively North and South of the town; the Phoenician-Punic temple located at the southern end of Capo San Marco. The promontory consists of pelitic and calcareous sediments of Messinian-Pliocene age overlain by Plio-Pleistocene basalts which, by selective erosion, form the hilltop plateau. A sequence of Pleistocene deposits, both marine and continental, testifying to several eustatic fluctuations, is closed by, a thick deposit of aeolic sandstones, related to the Wurm glaciation. Large sectors of the peninsula are buried by, recent dune and beach deposits. The geological structure of the promontory exerted a tight control on the geomorphologic features: three hilltop plateaux mark the main areas of basalt outcrop, bounded by steep scarps subject to rock fall and toppling processes. Slope instability processes are also present on the Mio-Pliocene pelitic outcrops where slides, both rotational and translational, develop and where the pelitic sequence is overlain by layers of hard rock, complex slope movements are present. Cliff retreat and landslide reactivation are controlled by, sea erosion on the western side of the peninsula which is exposed to the prevailing winds. In four cases archaeological sites are threatened by hydrogeological hazard: part of the urban area, the two necropolises of San Giovanni and San Marco and the ruins of a small temple, dating back to the Phoenician-Punic period, located on the southern end of Capo San Marco. All these sites are affected by different instability processes, related to particular geological and geomorphologic features. In this paper the four cases are analysed in detail to reach a complete geomorphologic characterisation; this is the starting point for the planning of remedial measures.