The ﬂuid-dynamics and compositional space-time evolution in subsurface environments of magmas with different bulk composition, water and carbon dioxide content, is computed using the GALES ﬁnite element code (Longo et al., 2006, doi: 10.1029/2006GL027760), which employs a multicomponent non-ideal volatile saturation model (Papale et al., 2006, doi: 10.1016/j.chemgeo.2006.01.013). Stability and robustness of the numerical algorithm are achieved through Galerkin least squares and discontinuity capturing terms. Two volcanic system conﬁgurations are considered: a vertical dike ﬁlled with compositionally stratiﬁed basaltic magma, and a closed phonolitic magma chamber connected to a reﬁlling dyke hosting trachite. Both vertical density distributions are gravitationally unstable, resulting in the ascent of light volatile rich magma and onset of convection and mixing. Parametric studies are carried out on the volatile content, system geometry, and reﬁlling conditions. Numerical results show the main role of the gravitational force in triggering convection, and highlight the critical role of carbon dioxide in enhancing convection and mixing efﬁciency. Complex patterns of ﬂow variables are found to characterize the convection dynamics, with transients in pressure distributions and development of multiple vortexes previously never described. Depending on the speciﬁc simulation conditions, the convection and mixing dynamics can result in compositional distributions where one of the two original compositions dominates or disappears from the system as a separate, well-identiﬁed compositional term.
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