The earliest known eruptive products are dated 47,000 years before present (BP). The Campi Flegrei caldera formed following two large explosive eruptions, the massive Campanian ignimbrite about 36,000 years BP, and the >40 cu km Neapolitan Yellow Tuff (NYT) about 15,000 years BP. Following eruption of the NYT a large number of eruptions have taken place from widely scattered subaerial and submarine vents. Most activity occurred during three intervals: 15,000-9500, 8600-8200, and 4800-3800 years BP. Two eruptions have occurred in historical time, one in 1158 at Solfatara and the other in 1538 that formed the Monte Nuovo cinder cone.
Episodes of dramatic uplift and subsidence within the caldera have occurred since Roman times. Evidence of this can be seen at many places, e.g. at the submerged ruins of a Roman city offshore the small town of Baia. The most recent episodes of uplift ones took place from 1969-72 and 1982-84, when the inhabitants of the area, Pozzuoli in particular, were witness to and victims of a phenomenon where the earth's surface rose; within a few months it had risen by a total of 3.5 m. This phenomenon is called bradisism (literally a slow movement of the earth's surface, as opposed to fast movement due to an earthquake).
The place which, more than any other, can be considered the evidence over the centuries of Phlegraean bradisism is the macellum (a market of the Roman period, better known as the Temple of Serapide) situated close to the port of Pozzuoli. The remains of this building (which dates back to the end of the first century A.D.) have been very useful in reconstructing the development of bradisism thanks to the holes made by lithodomes (sea molluscs which live in coastal areas on the shore line between high and low tide) on the columns which provide evidence of the variations in ground level as compare to sea level, from the IV century A.D. onwards.
Sources: adapted from GVP, Smithsonian Institution and the website of the Vesuvius Observatory
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