Skip to content

Effect of bubbles on the rheology of crystal-rich magma

Weiwei Ma , Pranabendu Moitra

Abstract

Understanding the flow behavior of the multi-phase magma is essential for constraining magma storage and ascent dynamics, eruption styles, and therefore, volcanic hazard assessment. While magma rheology provides a fundamental control on magma flow dynamics, the combined effects of bubbles and crystals with variable shapes on the rheology of three-phase magma have remained poorly constrained. Using dynamically similar analog experiments with glass spheres and high aspect ratio wollastonite particles (as crystal analogs), gas bubbles, and Newtonian silicone oil (as silicate melt analog), we characterize the rheology of three-phase magma under shear deformation. Rheometric data were collected using an MCR 702e MultiDrive rheometer, equipped with parallel plate and concentric cylinder geometries. Preliminary results suggest that a small bubble volume fraction slightly increases the viscosity of the particle-free suspending liquid, whereas it reduces the overall viscosity of a dense particulate suspension. We systematically explore the effects of particle volume fraction, particle shape, and bubble volume fraction on the rheological properties of our analog suspensions. The experimental stress-strain rate data were fitted to the Herschel-Bulkley model to obtain the rheological parameters: yield stress, consistency, and flow index. The implications of our findings for the dynamics of three-phase magma in crustal reservoirs and during effusive-explosive volcanic eruptions are discussed.