The water supply system of Ancient Pompeii (Southern Italy): From resource to Geohazard.

Pompeii, a famous ancient city in the southern Italy, was finally demised by the Plinian eruption in the 79 AD, but, long before it was hit by two alluvial mass flows that damaged the city. These pre-79 AD volcaniclastic deposits had been emplaced by avalanches, slumps, and associated debris flows (secondary lahars) during volcanically quiescent phases of the Somma-Vesuvius volcano. These deposits were transported and channelized along stream beds. Some of these extended to the immediate proximity of Capua Gate, at the northern side of Pompeii, where an artificial canal was built to supply water to the city. The canal path continues toward Vesuvius Gate and then, toward Villa of Mysteries. The flood deposits were released from hyperconcentrated slumps and debris flows. The first flood event, not transported through the artificial canal, took place before the foundation of the city (764 BC) and has affected a wide area of the Sarno Plain. The second one, occurred during the fourth century BC, was caused by the canal’s limited width and produced severe damage in the archaic city. Instead, the third flood event occurred in 170 BC and caused severe damage in the northern part of the city. The geological data prove that the water, as resource, in some cases can turn into a geohazard.