Precursors to the Plinian eruptions of Thera (Late bronze age) and Vesuvius (AD 79): Data from archaeological areas

Volcanological studies in the Bronze Age settlement of Akrotiri (Santorini, Greece) and in the Roman towns of Pompeii and Herculaneum (Vesuvius, Italy) provided information about the precursory phenomena preceding the Minoan and AD 79 plinian eruptions. Both the eruptions were characterised by seismic precursors with very different magnitudes and effects. The Minoan eruption was preceded by strong earthquake(s) that destroyed the Akrotiri settlement and forced an early evacuation of the island before the onset of the eruption. Instead, only some low magnitude shakings occurred before the AD 79 eruption of Vesuvius, which caught Roman towns and their inhabitants in the middle of their every-day life. Clear evidences of real volcanic precursors (both magmatic and phreatic) are not recorded in the deposits of the two eruptions. The onset of volcanic activity in both cases was represented by phreatomagmatic pulses of low energy shortly followed by the main eruption.