Quasistatic Modeling of Inelastic Deformation in the Sill Inflation and Caldera Floor Uplift of Sierra Negra, Galápagos Islands
William Donnelly pictured with black framed rectangular glasses and a green collared shirt

William Donnelly
MS Candidate

Advisor: Dr Shuo Ma
Wednesday, June 30, 2021
9 am

We model the sill inflation and caldera floor uplift at Sierra Negra volcano of Gal├ípagos Islands by incorporating inelastic deformation. Geodetic observations indicate that the caldera floor of Sierra Negra experienced up to 6.5 m uplift before the 2018 eruption. The uplift is modeled here by a quasistatic finite-element code incorporating a Drucker-Prager yield criterion within the caldera. We show that for a shallow magma source (a sill at 2.2 km depth) the low confining stress within the caldera can lead to extensive inelastic failure, largely due to near-surface dilation caused by sill inflation. Widespread inelastic deformation produces significantly larger caldera floor uplift than a purely elastic model for the same overpressure at the sill. Purely elastic deformation models thus can overestimate the volume of magma during the sill inflation phase. We also show that inelastic deformation significantly affects the stress field within the caldera and causes more horizontal compression on the inward-dipping intra-caldera ring fault, which may play an important role in the dynamics of ring-fault ruptures leading to volcanic eruption. The inelastic deformation and ring-fault rupture may explain anomalous tsunami generation of several CLVD volcanic earthquakes in a submarine setting.