Simulations of magma withdrawal from compositionally zoned bodies

A model based on numerical solution of the governing conservation equations has been devised in order to investigate the dynamics and systematics of central vent and ring fracture eruptions from flat-roofed and sloped-roof magma bodies strongly zoned in density and viscosity. Scale analysis of the conservation equations together with about 150 numerical experiments enables development of quantitative correlations for the mass discharge, M, and the duration of mixed magma eruption, Δt, with the effective driving pressure, σ. Natural eruptions span the entire range of dynamic regimes from viscous through inertial. Several scenarios for producing variable discharge during a single eruptive phase were also studied. It is demonstrated quantitatively that compositional gaps and episodes of mixed-magma eruption can originate due to the withdrawal process itself and are not necessarily related to pre-eruptive gradients within the magma body. -from Authors