Characterisation of juvenile pyroclasts from the Kos Plateau Tuff (Aegean Arc): insights into the eruptive dynamics of a rhyolitic caldera-forming eruption

C. Bouvet (1) , Olivier Bachmann (2) , Alain Burgisser (3)

1 University of Geneva, Dept. of Mineralogy
2 Department of Earth and Space Sciences [Seattle]
3 Alaska Volcano Observatory

AB: Silicic pumices formed during explosive volcanic eruptions are faithful recorders of the state of the magma in the conduit, close to the fragmentation level, as viscosity is generally high enough to limit their post-fragmentation deformation to a minimum. Pumice textures are therefore of great interest to shed light into bubble nucleation, growth and coalescence in silicic magmas ascending in a volcanic conduit, which ultimately controls the style of eruption. In this study, we have characterised the pumices produced by the rhyolitic 161 ka Kos Plateau Tuff (KPT) eruption, Aegean Arc, Greece. Four types of pumices were distinguished macroscopically in the non-welded deposits, and have been characterized using thin section observation, SEM imagery, porosimetry, and permeametry. We show that the types of pumices defined are confirmed by distinct petrophysical characteristics, and the measured differences in porosity and permeability are the result of either conduit processes, differences in crystallinity or magma mixing. We also show that permeability does not depend solely on porosity, as implied by the percolation theory. Size of pore aperture, tortuosity and pathway wall rugosity also play a fundamental role in the flow of gas through the permeable magmatic foam.

Domains: Volcanology

C. Bouvet, Olivier Bachmann, Alain Burgisser. Characterisation of juvenile pyroclasts from the Kos Plateau Tuff (Aegean Arc): insights into the eruptive dynamics of a rhyolitic caldera-forming eruption. AGU Meeting San Francisco, Dec 2007, San Francisco, United States. 1 p. ⟨insu-00212239⟩