Publication details for Dr Ed LlewellinLlewellin, E.W. & Manga, M. (2005). Bubble suspension rheology and implications for conduit flow. Journal of Volcanology and Geothermal Research 143(1-3): 205-217.
- Publication type: Journal papers: academic
- ISSN/ISBN: 0377-0273
- DOI: 10.1016/j.jvolgeores.2004.09.018
- Keywords: magma rheology; bubble suspension; conduit-flow model; eruption model; capillary number
- View online: Online version
- Durham research online: DRO record
Author(s) from Durham
Bubbles are ubiquitous in magma during eruption and influence the rheology of the suspension. Despite this, bubble-suspension rheology is routinely ignored in conduit-flow and eruption models, potentially impairing accuracy and resulting in the loss of important phenomenological richness. The omission is due, in part, to a historical confusion in the literature concerning the effect of bubbles on the rheology of a liquid. This confusion has now been largely resolved and recently published studies have identified two viscous regimes: in regime 1, the viscosity of the two-phase (magma–gas) suspension increases as gas volume fraction phi increases; in regime 2, the viscosity of the suspension decreases as phi increases. The viscous regime for a deforming bubble suspension can be determined by calculating two dimensionless numbers, the capillary number Ca and the dynamic capillary number Cd. We provide a didactic explanation of how to include the effect of bubble-suspension rheology in continuum, conduit-flow models. Bubble-suspension rheology is reviewed and a practical rheological model is presented, followed by an algorithmic, step-by-step guide to including the rheological model in conduit-flow models. Preliminary results from conduit-flow models which have implemented the model presented are discussed and it is concluded that the effect of bubbles on magma rheology may be important in nature and results in a decrease of at least 800 m in calculated fragmentation-depth and an increase of between 40% and 250% in calculated eruption-rate compared with the assumption of Newtonian rheology.