Up and Down: Lake Bolsena Water-Level Variation in the Bronze Age and Iron Age

Lake Bolsena is located in the Bolsena caldera, part of the Vulsini Mountains complex which consists of multiple volcanoes and craters. The lake is now located 305 m above sea level, covers an area of about 114.5 km2 and has a maximum depth of 151 m. It is most likely in equilibrium with an aquifer in the pyroclastic permeable rocks that make up the basin and has a natural outlet - the river Marta – that is active all year and drains to the Tyrrhenian Sea. A range of evidence clearly indicates that in ancient times the lake level was much lower. Starting from the Middle Bronze Age, a series of settlements, including the Gran Carro, were in fact located along the 297m isobath. It is still unclear whether their abandonment was driven directly by rising waters and the associated shift in the lake shoreline or by earlier socioeconomic factors. To address this issue, several studies were performed on the evolution of the lake shore over the centuries, using the available archaeological data, historical sources and geological information. In this study we analyze a sediment core (Bolsena-1) taken in the lake near the Gran Carro settlement, using mineralogical and geochemical analytical techniques. Our aim is to better understand the lake level fluctuations during the life of the settlement. Statistical analysis (PCA) of the analytical data and archaeobotanical data obtained for the Bolsena-1 core allowed the recognition of four phases of Lake Bolsena water level fluctuation within an overall rising trend: two cycles of raising and submersion, alternating with lowering and relatively dry habitat. The temporal pattern and magnitude of these cycles are compared to earlier published results for the period concerned.