Timescales and magma dynamics of the plumbing system feeding a Plinian eruption: the 79 CE eruption of Somma-Vesuvius, Italy

Plinian eruptions are the most common high impact explosive events, causing severe local impacts and influencing human settlement or migration and global climate. Understanding their pre-eruptive processes and timescales is crucial for forecasting eruptions and mitigating hazards. The iconic 79 CE Somma-Vesuvius eruption (Italy) is considered the archetype of Plinian eruptions. However, knowledge of its plumbing system architecture and pre-eruptive magmatic processes remains incomplete. Chemical and isotopic data, clinopyroxene zoning analysis, and numerical modelling reveal a vertically extended plumbing system with deep mafic magma batches refilling a tephri-phonolitic reservoir multiple times before the eruption. Diffusion modelling constrains recharge events in timescales from decades to less than a year, which align with historically well-documented seismicity (“non desiit enim assidue tremere Campania”, Seneca; “Praecesserat per multos dies tremor terrae”, Pliny the Younger) preceding the eruption. These findings enhance our understanding of volcanic behaviour, aiding in hazard assessment and risk mitigation for future similar eruptions.