Distal Pyroclastic Current Deposits of the 79 AD Vesuvius Eruption on the Mountains Adjacent to the Campanian Plain

Literature data show that the two most widespread Vesuvius 79 AD pyroclastic density currents (PDCs) have been traced over a large area around the volcano throughout the Campanian plain. Here, we present stratigraphic and volcanological evidence for 79ADPDC deposits on higher elevated areas bordering the Campanian plain. More specifically, a sequence of ash deposits, with erosive basal contacts, interstratified with lithic-rich lapilli fall layers (D, G1, G3, I, and X2), has been observed above a thick pumice blanket that has been associated with the Plinian phase on the Lattari mountains between 50 and 300 m asl. We use fall layers as guide levels that allow the correlation of the distal ash deposits with the proximal/medial stratigraphic sequences. The ash PDC sequence ranges in thickness from 22 cm (where local debris flows partially erode it) to 150 cm (where it thickens against anthropic structures). This study demonstrates that most PDC units recognized in medial areas, including the final phreatomagmatic events, are traceable on mountain slopes about 20 km from the vent. The discovery of PDC units at altitudes as high as 300 m asl adjacent to the Campanian plain suggests an inflated and turbulent nature of the parental pyroclastic currents and a limited shielding effect of the mountains to the spread of the PDCs.