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Outgassing behaviour during highly explosive basaltic eruptions

Emily C. Bamber1\, Giuseppe La Spina2, Fabio Arzilli3, Margherita Polacci4, Lucia Mancini5, Mattia de' Michieli Vitturi6, Daniele Andronico2, Rosa Anna Corsaro2 and Mike R. Burton4

  • Affiliations: 1 Institute of Science, Technology and Sustainability for Ceramics (ISSMC), National Research Council (CNR), Faenza, Italy 2 Istituto Nazionale di Geofisica e Vulcanologia - Osservatorio Etneo, Sezione di Catania, Catania, Italy 3 School of Science and Technology, Geology Division, University of Camerino, Italy 4 Department of Earth and Environmental Sciences, The University of Manchester, Manchester, UK 5 Department of Materials, Slovenian National Building and Civil Engineering Institute (ZAG), Ljubljana, Slovenia 6 Istituto Nazionale di Geofisica e Vulcanologia, Sezione di Pisa, Pisa, Italy

  • Presentation type: Talk

  • Presentation time: Monday 16:00 - 16:15, Room S160

  • Programme No: 3.16.2

  • Theme 3 > Session 16

Abstract

The low viscosity of crystal-poor basaltic magma typically prevents brittle magma fragmentation. However, highly explosive basaltic Plinian eruptions do occur, presenting a considerable hazard. The explosivity of a volcanic eruption relates to the efficiency in which the gas and melt phases are able to separate during magma ascent. If outgassing is facilitated, an effusive eruption is likely. Instead, if the gas and melt phases remain coupled during magma ascent, a highly explosive eruption may result. Outgassing efficiency is controlled by magma permeability and the development and maintenance of permeable networks within the magma. Yet, estimates of magma permeability from pyroclasts of basaltic eruptions of varying explosivity overlap, indicating a possible complex relationship between permeability, outgassing and eruptive style.  We present 3D measurements of vesicle textures, including porosity, connectivity, tortuosity and the throat-pore size ratio for pyroclasts of 3 basaltic Plinian eruptions of the Las Sierras-Masaya and Etna volcanic systems, acquired using phase-contrast synchrotron-based X-ray computed microtomography. We compare our results from Plinian pyroclasts with those from lava fountain activity. We use these data in a 1D steady-state magma ascent model to investigate how controls on magma permeability influence eruptive style, finding that the bubble number density and gas-melt friction largely influence explosivity. However, for fast ascending magmas, gas-melt coupling is maintained independent of magma permeability. In this case, pre-eruptive conditions such as the initial temperature and crystal content have an important role in controlling the transition between a Plinian eruption and lava fountain activity at basaltic volcanoes.