Thermomechanics of shallow magma chamber pressurization: Implications for the assessment of ground deformation data at active volcanoes

•We develop a dynamic model for calculating magma chamber pressurization.•An adaptive boundary allows reservoir expansion in response to overpressure.•Overpressures are 60-70% less than calculated with a fixed boundary condition.•Large overpressures are not generated in magma chambers ⩾100 km3.•Application to Santorini suggests modest overpressures during the recent inflation.

In this study, we utilize thermomechanical models to investigate how magma chambers overpressurize as the result of either magmatic recharge or volatile exsolution. By implementing an adaptive reservoir boundary condition we are able to track how overpressure dissipates as the magma chamber expands to accommodate internal volume changes. We find that the size of the reservoir greatly impacts the resultant magma chamber overpressure. In particular, overpressure estimates for small to moderate-sized reservoirs (1-10 km3) are up to 70% lower than previous analytical predictions. We apply our models to Santorini volcano in Greece where recent seismic activity and ground deformation observations suggested the potential for eruption. The incorporation of an adaptive boundary condition reproduces Mogi flux estimates and suggests that the magma reservoir present at Santorini may be quite large. Furthermore, model results suggest that if the magma chamber is >100 km3, overpressures generated due to the high magma flux may not exceed the strength of the host rock, thus requiring an additional triggering mechanism for eruption. Although the adaptive boundary condition approach does not calculate the internal evolution of the magma reservoir, it represents a fundamental step forward from elastic Mogi models and fixed boundary solutions on which future investigations of the evolution of the magma can be built.