Skip to content

A constitutive equation for the viscosity of bubbly magmas

Gaetano Ferrante 1, Helge Gonnermann1, Céline Fliedner1,2, Thomas Giachetti3, Amy G. Ryan1

  • Affiliations: 1Department of Earth, Environmental and Planetary Sciences, Rice University, 6100 Main St, Houston, 77005, TX, USA; 2TotalEnergies S.E., Avenue Larribau, Pau, 64018, France; 3Department of Earth Sciences, University of Oregon, 1585 E 13th Ave, Eugene, 97403, OR, USA

  • Presentation type: Poster

  • Presentation time: Monday 16:30 - 18:30, Room Poster Hall

  • Poster Board Number: 220

  • Programme No: 3.6.24

  • Theme 3 > Session 6

Abstract

The eruptive dynamics of a volcano are largely determined by the rheology of its magmas. Bubbles in magma have been shown to either increase or decrease its viscosity, primarily depending on the balance between the viscous stresses that deform the bubbles and surface tension which acts to restore their sphericity, encapsulated by the Capillary number. Despite the growing number of experimental studies investigating the rheology of bubbly fluids, a definitive constitutive relation between the viscosity η of a magma and its bubble volume fraction φ is still lacking. Here, we show results of new viscosity measurements on rhyolitic magma at high Capillary numbers, with bubble volume fractions between 0.15 and 0.80. We deformed pumice samples from Medicine Lake Volcano, California in combined torsion-compression experiments at a temperature of 975 °C and shear strains up to ∼3. Based on our experimental results, we define a new constitutive relation for the