Geomorphological and archaeological evidence of the ground movements (bradyseisms) in the Phlegraean Fields (Naples, Italy)

Abstract At present the Phlegraean coast is an area of volcanic activity, whose most striking features are the vertical movements of the ground (bradyseisms), intense smoking (Solfatara), hydrothermalism and microseismic activity. The re-examination and reinterpretation of historical events, geomorphological data and the sedimentary series that characterize the numerous archaeological sites along the Phlegraean coast, have allowed us to reconstruct more accurately the history of the vertical movements of the earth (bradyseisms) and the geomorphological evolution of the coast during the last two thousand years. In some archaeological contexts examined, sea and/or beach sediments have been encountered, containing the relative traces of erosion, giving evidence of various episodes of submersion of the Phlegraean coast, dating back at least to the 4th century A.D. This fact is due to the progressive bradyseismic sinking of the ground, which with the passing of time and up to the late Roman period consigned vast continental areas to the sea. Sea sediments alternate in places with subaerial deposits often associated with anthropic layers and archaeological ruins. These data seem to be connected to the persistence of long or short pauses in the general bradyseismic sinking or can result from clear episodes of rising (inversion of movement) probably at the approach of a volcanic paroxysm which in at least one case coincided with an eruption. The analysis of all information demonstrates that the Phlegraean coast has, over the last 2000 years, been subject to a progressive bradyseismic sinking interrupted in places by brief and violent episodes of rising. The submersion of the coast in the post-Roman age came about in three distinct moments: between the 4th and 5th century, between the 7th and 8th century and between the 14th and 15th century. The whole entity involved in the sinking was at least 17 m, of which only a part (6-7 m) has been regained to the above-water environment by the inversion of the movement. From the study it has emerged that archaeological remains often give evidence of the history of geomorphological events of localities; for this reason it has been possible to integrate all the information both published and unpublished of geoarchaeological importance in a homogeneous framework.