The 512 AD eruption of Vesuvius: complex dynamics of a small scale subplinian event |
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Authors: | R Cioni A Bertagnini D Andronico P D Cole F Mundula |
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Institution: | 1.Dip.to di Scienze della Terra,Università di Cagliari,Cagliari,Italy;2.Istituto Nazionale di Geofisica e Vulcanologia, sezione di Pisa,Pisa,Italy;3.Istituto Nazionale di Geofisica e Vulcanologia, sezione di Catania,Catania,Italy;4.Montserrat Volcano Observatory,Flemmings,West Indies;5.Seismic Research Centre,Trinidad and Tobago,West Indies |
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Abstract: | We describe the products of the hitherto poorly known 512 AD eruption at Vesuvius, Italy. The deposit records a complex sequence
of eruptive events, and it has been subdivided into eight main units, composed of stratified scoria lapilli or thin subordinate
ash-rich layers. All the units formed by deposition from tephra fallout, pyroclastic density currents of limited extent being
restricted to the initial stages of the eruption (U2). The main part of the deposit (U3 and U5) is characterized by a striking
grain size alternation of fine to coarse lapilli, similar to that often described for mid-intensity, explosive eruptions.
The erupted products have a phonotephritic composition, with progressively less evolved composition from the base to the top
of the stratigraphic sequence. Based on different dispersal, sedimentological and textural features of the products, we identify
five phases related to different eruptive styles: opening phase (U1, U2), subplinian phase (U3 to U5), pulsatory phreatomagmatic
phase (U6), violent strombolian phase (U7) and final ash-dominated phase (U8). A DRE volume of 0.025 km3 has been calculated for the total fallout deposit. Most of the magma was erupted during the subplinian phase; lithic dispersal
data indicate peak column heights of between 10 and 15 km, which correspond to a mass discharge rate (MDR) of 5 × 106 kg s−1. The lower intensity, violent strombolian phase coincided with the eruption of the least evolved magma; a peak column height
of 6–9 km, corresponding to an MDR of 1 ×10 6 kg s −1, is estimated from field data. Phreatomagmatic activity played a minor role in the eruption, only contributing to the ash-rich
deposits of U1, U4, U6 and U8. |
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