oa Numerical Simulation of Hour-Scale Magma Migration Using Pre-Eruptive Ground Deformation

Analysis of ground deformation around a volcano can provide magma accumulating process of plumbing system and infer invisible magma migration in the system. We developed a coupling scheme of modeling of magma plumbing system and magma flow simulation to quantitatively understand pre-eruptive magma migration in hour scale from observation of ground deformation. Our scheme was applied to ground deformation before an explosive eruption at the Showa Crater of Sakurajima volcano on April 9, 2009. The ground deformation shows that a periodic inflation and deflation event had lasted 30 hours before the eruption. Our model composed of shallower gas and deeper magma reservoirs connected by a volcanic conduit that had been suggested by the past geophysical observations. A pressure difference between the two reservoirs forces the magma to move from the deeper up to the shallower reservoir. We assumed a constant rate of magma supply to the deeper reservoir as an input to the magma plumbing system and a viscous magma flow in a cylindrical volcanic conduit. As a result of parametric inversion to reproduce the observed volumetric behavior, it is estimated that relatively high permeable magma ascends to the shallower in a volcanic conduit with 125 m radius. The result also shows that the gas in magma mainly ascends to the shallower and that the supply rate to the deeper reservoir on April 9 is ca. 16 m3/s. Finally, we found that our numerical scheme can provide the pre-eruptive magma migration in hour scale as well as constrain some unknown parameters.