Orvieto: a Case of an Unstable Town.

Orvieto, one of the major historic-artistic towns of Central Italy, lies in the province of Terni, about 100 km north of Rome, at the boundary between the Regions of Umbria and Latium. The town was built by the Etruscans in the IX-VIII century B.C., over a small tuffaceous cliff (about 1.3 km^2 in area). The town suffers from instability conditions, due to the particular geological and geomorphological features that are the main cause of the landslides affecting the cliff’s perimeter. The mass movements have produced, over time, a slow but inexorable degradation of the historic town, by progressively reducing its size. The aim of this excursion day is that of illustrating the geological-geomorphologic features of Orvieto’s Cliff, explaining the causes of the town’s instability, and describing the works (the majority of which were realized recently) aimed at the conservation and consolidation of the cliff and the historic center of town.