Abstract

We present a quantitative treatment of the macroscopic behaviour of a sheared magma using Biot's theory and a shear-dilatancy sensitive material model that captures the simultaneous change in pressure in the both the matrix and interstitial pore (melt) fluid. The calculations are relevant to a magma in the solidosity range 0.55-0.7 and applicable over a large range of melt compositions. The resulting excess pore pressure distribution is a function of the position and the time. A scaling emerges that enables the results to be presented in non-dimensional form. A sensitivity study of the parameters describing the rheology of the solid matrix (including permeability features) will be presented. The model enables the estimate of pressure and flow rates as a function of strain rate, thus opening a way of understanding the features in the crystal mush (grain size sorting, alignment and layering) that are caused by upflowing magma. At high strain rates ($>$10$^{-14}$s$^{-1}$) flow rates due to shear far exceed melt movement due to buoyancy effects.