Exploring the role of fluid-solid interactions for modelling volcano deformation

Investigating the temporal development of magma reservoir pressure and associated surface displacements can reveal fundamental aspects of subsurface magmatic processes and aid in eruption forecasting. The limitation with existing volcano deformation models is that they typically ignore magma intrusion dynamics and focus on the response of surrounding rocks to source boundary pressure. Magma fluid dynamics should be incorporated into magmatic modelling to track the temporal development of a system, instead of the widely used kinematic techniques. Here, we compare analytical and numerical solutions for magma intrusion into a shallow reservoir, using two schemes of intrusion boundary condition, inlet pressure and inlet mass flow. Model sensitivity tests are conducted to explore key factors controlling the two-way coupling between solid and fluid components, assuming an incompressible magma for a first-order approach. For intrusions of viscous magma (?10(8) Pa s) or a narrow feeder conduit (5-20 m), applying an inlet pressure causes the resultant pressure and surface deformation to develop at a very slow rate; lower viscosity magmas produce faster deformation rates. The mass flow boundary condition reduces the number of model parameters as it is independent of poorly constrained parameters such as conduit and magma characteristics. For both boundary conditions, reservoir pressurization, and hence spatio-temporal surface deformation, are strongly influenced by reservoir geometry due to geometric compressibility. Our results provide fundamental knowledge to advance to more complex coupled fluid-solid mechanics models in volcano geodesy.