The dark nature of Somma-Vesuvius volcano: Evidence from the 3.5 Avellino Eruption

The interpretation of high-resolution seismic profiles and core data collected in the western Somma-Vesuvius volcano documents a stratigraphic unit consisting of a voluminous debris avalanche that was covered by pyroclastic gravity current deposits after entering the sea. Based on the stratigraphic position together with the ages of the dated Somma-Vesuvius Plinian eruptions, this unit was linked to the similar to 3.5 ka-old Avellino Plinian eruption and correlated and mapped in offshore and onshore areas. The deposition of the thick Avellino unit had a strong impact on the physical environment of the volcano's western sector, producing hundreds of metres of prograding coastline and the formation of a morphological barrier in the alluvial plain. The striking erosional and depositional features that characterise the top of the Avellino unit along the coast suggest that the entrance of the debris avalanche into the sea triggered a tsunami that struck the Naples Bay coast. The hazardous geologic events include both the sea-facing flank failure of the volcano (producing the debris avalanche and tsunami) and the Avellino Plinian eruption (producing pumice fall and surge clouds) that profoundly affected several human settlements located within a 20 km radius of the volcano, causing the decline of the Bronze Age communities.