HR: 10:50h
AN: V22A-03 INVITED    [Abstracts]
TI: Texture and Composition of Pumice and Scoria Provide New Insights into the Dynamics of Explosive Eruptions at Campi Flegrei (Italy)
AU: * Polacci, M
EM: polacci@ct.ingv.it
AF: INGV-Sezione di Catania, Piazza Roma 2, Catania, 95125, Italy
AU: Piochi, M
EM: monky5@ov.ingv.it
AF: INGV-Osservatorio Vesuviano, via Diocleziano 328, Napoli, 80124, Italy
AU: De Astis, G
EM: gianfi@ov.ingv.it
AF: INGV-Osservatorio Vesuviano, via Diocleziano 328, Napoli, 80124, Italy
AU: Zanetti, A
EM: zanetti@crystal.unipv.it
AF: IGG-CNR-Pavia, via Ferrata 1, Pavia, 27100, Italy
AU: Mangiacapra, A
EM: annarita@ov.ingv.it
AF: INGV-Osservatorio Vesuviano, via Diocleziano 328, Napoli, 80124, Italy
AU: Vannucci, R
EM: vannucci@crystal.unipv.it
AF: IGG-CNR-Pavia, via Ferrata 1, Pavia, 27100, Italy
AU: Giordano, D
EM: dgiordan@uniroma3.it
AF: Dipartimento di Scienze Geologiche, Università di Roma Tre, Largo San Leonardo Murialdo 1, Roma, 00154, Italy
AB: Campi Flegrei (CF), a nested caldera located west of the densely-inhabited city of Naples, has been the site of volcanic activity for the past 60 ka BP. The last eruption occurred in AD 1538, but geochemical and geophysical signals have been monitored for the last tens of years clearly indicating that the magmatic system is still active. Volcanic risk mitigation in this area is therefore a primary goal of the scientific community. Here we combine new and literature data on the texture and composition of pumice and scoria clasts of selected CF eruptions with the goal to investigate their relationship to, and implications for, the eruption dynamics. We focus on three events with decreasing eruption intensity and magnitude: the Campanian Ignimbrite (39 ka), Agnano Monte Spina (4.1 ka) and Monte Nuovo (AD 1538) eruptions. Previous studies indicate that phenocryst and major element bulk compositions, as well as the original volatile content, are comparable in samples from the investigated eruptions. From these observations we derive that similar pre-eruptive physico-chemical conditions governed magma storage in the shallow crust before the occurrence of the above eruptions. Our investigation displays however a significant heterogeneity among the studied samples in terms of crystal and vesicle texture and abundance, composition of microlites and glassy groundmass, residual groundmass water content, and, finally, rheological properties of the related magmas. We ascribe such textural, compositional and rheological variability to different mechanisms of volatile exsolution, separation from the melt and outgassing accompanying magma ascent along the conduit and generated primarily by changes in the magma ascent rate. Low ascent rates allow open-system degassing, groundmass crystallization in response to water exsolution and the development of permeable flow pathways through which volatiles escape non-explosively to the surface potentially decreasing the overall eruption explosivity, as in the case of Monte Nuovo. Faster ascent rates instead inhibit crystal nucleation and growth and promote syn-eruptive vesiculation under closed-system conditions, which, in turn, translates into eruptions of higher explosivity (i.e. Campanian Ignimbrite or Agnano Monte Spina). Because our study indicates that magma ascent rate was the key-parameter in driving the diversity of eruptive intensity and style of activity observed at CF, we conclude that future research should be aimed at quantifying factors generating changes in such parameter and at integrating geochemical and geophysical models for a comprehensive understanding of the eruption dynamics in this hazardous volcanic area.
DE: 8414 Eruption mechanisms and flow emplacement
DE: 8428 Explosive volcanism
DE: 8434 Magma migration and fragmentation
DE: 8439 Physics and chemistry of magma bodies
DE: 8488 Volcanic hazards and risks
SC: Volcanology, Geochemistry, Petrology [V]
MN: 2007 Fall Meeting