A porous flow model of magma migration within Mt. Etna: The influence of extended sources and permeability anisotropy

The isotropic point-source model of porous flow proposed by Bonafede and Boschi is employed to model magma flow within the edifice of Mt. Etna in probabilistic terms. The flow pattern is found to be nearly horizontal, suggesting magma propagation through lateral dykes departing radially from the central conduits. The point source model is able to provide a detailed description of eruption site distribution for a few sections of Mt. Etna, but it fails to explain simultaneously the eruption distribution along the mutually orthogonal N–S and E–W sections. The solution is then generalized to deal with extended sources and with anisotropic media, employed, respectively, to simulate a hypothetical N–S-trending fracture system at the base of the volcano or the influence of the regional stress field on the directional probability of dyke opening. The results show that both models are able to explain the presence on Mt. Etna of the N–S-trending rift. In particular, the anisotropic model provides the best fits to the north, south, west and east topographic sections. Several features of the eruption distribution on Mt. Etna remain unexplained, however, by a porous flow model and apparently require the intervention of specific structural effects. For instance, a detailed reproduction of the three-lobe distribution of eruptive sites (observed in recent historic times) seems to require permeability heterogeneities, the effect of local topographic loading or the presence of a local axial stress field related to the inflation of Mt. Etna.