The influence of regional stresses on the mechanical stability of volcanoes: Stromboli (Italy)

An elastic model was developed to study the mechanical stability of a volcanic system that includes a volcanic edifice and a magmatic feeding system with axial symmetry around a vertical axis. Stability depends critically on the horizontal regional stress which comes into the problem as a boundary condition imposed at large horizontal distance. Three types of boundary condition were considered (1) zero horizontal displacement (NHD); (2) lithostatic regional stress (LITH); (3) non-axisymmetrical regional stress corresponding to a strike-slip regime (NAS). The model is applied to Stromboli volcano, which is characterized by a steep volcanic edifice and open conduits filled with magma. It is found that the deep reservoir has no influence on the stability of the edifice. Both NHD and LITH conditions imply that the regional horizontal stress is isotropic which is not appropriate for the Southern Tyrrhenian Sea. With the NAS boundary condition, the stability of the plumbing system of Stromboli volcano places an upper limit on the maximum shear stress Δ0=(|σh|max-|σh|min)/2. For Δ0=10 MPa, the magmatic feeding system is at the limit of mechanical instability.