Rheological effects in volcano deformation modelling

The build-up of magma beneath a volcano can be revealed by ground surface deformation, and the recorded surface displacement can be modelled to infer details of the magma system dynamics. Constraints on magmatic processes can then be used to aid hazard assessment and eruption forecasting. However, inferring the processes occurring in the magma plumbing system during volcano deformation episodes is inherently dependent on the modelling approach used to interpret the recorded deformation data, and in particular the choices of rheology used to represent the solid and fluid parts of the magmatic and host rock system. Here, we explore the elastic, viscoelastic, and poroelastic rheologies typically implemented in volcano deformation analyses, and assess how their choices impact the interpretation of recorded volcano deformation data. Different viscoelastic rheologies can produce drastically different predicted surface deformation patterns, but all viscoelastic rheologies will typically lead to different source pressurisation estimates compared to a linear elastic rheology. Poroelastic source implementations can produce surface deformation even after supply to a reservoir has stopped, due to diffusive redistribution of pore pressures. Both viscous and poroelastic processes add a time-dependent component to the stress-strain evolution, which changes model predictions of temporal volcano deformation. Consequently, when applied to interpret recorded deformation, viscous and poroelastic rheologies can suggest non-linear magma system dynamics that are not captured by a simpler purely elastic model rheology. Issues persist with reliably parameterising different rheological approaches but their importance in modifying surface deformation predictions cannot be overlooked.