The AD 79 Vesuvius eruption revisited

The fall and pyroclastic density current deposits stratigraphy of the AD 79 eruption of Vesuvius is comprehensively reappraised, yielding a more accurate picture of how the 31 hr duration eruption evolved with time and space. The Plinian fall deposit was one of the earliest to be treated with a modern volcanological approach. Twelve lithostratigraphic units within the pumice fall sequence (7 in the ‘White Pumice Deposit’; 5 in the ‘Grey Pumice Deposit’) are distinguished by variations in grain size and the ratio of lithic to juvenile clasts (based on 459 samples) and show that the Plinian plume fluctuated between 14 and 34 km in height, depositing 6.4 km3 of tephra in 17 h. Five post-Plinian lithic-rich fall layers are recognized, each recording a subPlinian event that persisted for several tens of minutes. Seventeen pyroclastic density currents (PDCs) formed before, during, and after the Plinian phase, and are recorded by 27 defined and mapped lithostratigraphic units 15 of which show significant lateral and vertical variations in lithofacies (417 samples analysed). The minimum total volume of PDC deposits is 1.25 km3. The post-Plinian phase spanned 14 h. Proximal lithic breccias 30 m thick may record subsidence at source. The most powerful PDC (p-PDC 13) had the greatest runout. As it waxed its footprint gradually increased radially, reaching a distance of 25 km from source and surmounting hills >800 m above sea-level. The eruption ended at 8.05 pm on the second day, leaving behind a widespread trail of devastation.