Campi Flegrei
The Campi Flegrei caldera, on the other side of the Bay of Naples to Vesuvius, is a nested structure generated by two large and explosive eruptions: the Campanian Ignimbrite (37,000 years BP) and the Neapolitan Yellow Tuff (12,000 years BP). During the past 12,000 years volcanic activity has been very intense, accompanied by deformation of the caldera floor. The system is still active, as testified by the most recent eruption of 1538 AD, recent unrest episodes (1969-1972 and 1982-1984) and intense fumarolic and hot spring activity. The caldera and its surroundings are inhabited by more than 1.5 million people. Therefore, the level of volcanic risk is extreme.
The Campi Flegrei system is the "large" end member of our spectrum of focus volcanic systems, with the added importance that eruptions of the size known to have occurred here have not been observed or recorded, so conditions of magma storage and processing are intractable via real time geophysical methods and must be approached via the only record available, namely the rocks produced during eruptions.