Experimental constraints on the outgassing dynamics of basaltic magmas

L. Pioli*, C. Bonadonna, B. J. Azzopardi, J. C. Phillips, M. Ripepe

*Corresponding author for this work

Research output: Contribution to journalArticle (Academic Journal)

32 Citations (Scopus)

Abstract

The dynamics of separated two-phase flow of basaltic magmas in cylindrical conduits has been explored combining large-scale experiments and theoretical studies. Experiments consisted of the continuous injection of air into water or glucose syrup in a 0.24 m diameter, 6.5 m long bubble column. The model calculates vesicularity and pressure gradient for a range of gas superficial velocities (volume flow rates/pipe area, 10(-2)-10(2) m/s), conduit diameters (10(0-2) m), and magma viscosities (3-300 Pa s). The model is calibrated with the experimental results to extrapolate key flow parameters such as C-o (distribution parameter) and Froude number, which control the maximum vesicularity of the magma in the column, and the gas rise speed of gas slugs. It predicts that magma vesicularity increases with increasing gas volume flow rate and decreases with increasing conduit diameter, until a threshold value (45 vol.%), which characterizes churn and annular flow regimes. Transition to annular flow regimes is expected to occur at minimum gas volume flow rates of 10(3)-10(4) m(3)/s. The vertical pressure gradient decreases with increasing gas flow rates and is controlled by magma vesicularity (in bubbly flows) or the length and spacing of gas slugs. This study also shows that until conditions for separated flow are met, increases in magma viscosity favor stability of slug flow over bubbly flow but suggests coexistence between gas slugs and small bubbles, which contribute to a small fraction of the total gas outflux. Gas flow promotes effective convection of the liquid, favoring magma homogeneity and stable conditions. Citation: Pioli, L., C. Bonadonna, B. J. Azzopardi, J. C. Phillips, and M. Ripepe (2012), Experimental constraints on the outgassing dynamics of basaltic magmas, J. Geophys. Res., 117, B03204, doi: 10.1029/2011JB008392.

Original languageEnglish
Article number03204
Number of pages17
JournalJournal of Geophysical Research: Earth Surface
Volume117
DOIs
Publication statusPublished - 8 Mar 2012

Keywords

  • VISCOUS-LIQUIDS
  • GAS-LIQUID FLOW
  • SLUG FLOW
  • CHURN FLOW
  • REGIME TRANSITION
  • MOUNT-ETNA
  • BREAK-UP
  • VERTICAL 2-PHASE FLOW
  • BUBBLE-SIZE DISTRIBUTIONS
  • STROMBOLI VOLCANO

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