Thermomechanical controls on magma supply and volcanic deformation: application to Aira caldera, Japan

ArticleGround deformation often precedes volcanic eruptions, and results from complex interactions between source processes and the thermomechanical behaviour of surrounding rocks. Previous models aiming to constrain source processes were unable to include realistic mechanical and thermal rock properties, and the role of thermomechanical heterogeneity in magma accumulation was unclear. Here we show how spatio-temporal deformation and magma reservoir evolution are fundamentally controlled by three-dimensional thermomechanical heterogeneity. Using the example of continued inflation at Aira caldera, Japan, we demonstrate that magma is accumulating faster than it can be erupted, and the current uplift is approaching the level inferred prior to the violent 1914 Plinian eruption. Magma storage conditions coincide with estimates for the caldera-forming reservoir ~29,000 years ago, and the inferred magma supply rate indicates a ~130-year timeframe to amass enough magma to feed a future 1914-sized eruption. These new inferences are important for eruption forecasting and risk mitigation, and have significant implications for the interpretations of volcanic deformation worldwide.This work was supported by the European Commission, Framework Program 7 (grant 282759, “VUELCO”, and grant 308665, “MEDSUV”), the Natural Environmental Research Council (NE/G01843X/1, “STREVA”, and “COMET”), the Royal Society (UF090006), the University of Bristol International Strategic Fund, and the MEXT project (Ministry of Education, Culture, Sports, Science and Technology). We thank Paul Alanis for the seismic tomography data, Keigo Yamamoto for the levelling data, and Takeshi Tameguri for the VT data. We thank Jon Blundy and Kathy Cashman for feedback on an early version of the manuscript

The transcrustal magma reservoir beneath Soufrière Hills Volcano, Montserrat: insights from 3‐D geodetic inversions

This is the final version. Available on open access from Wiley via the DOI in this recordWe invert intraeruptive ground displacements recorded between 2003 and 2005 on Montserrat to shed light on the magmatic plumbing system of Soufrière Hills Volcano. Incorporating 3‐dimensional crustal mechanical and topographic data in a finite‐element model, we show that the recorded displacements are best explained by a southeastward dipping (plunge angle of 9.3°) vertically extended triaxial ellipsoidal pressure source with semiaxes lengths of 1.9 and 2.0 km horizontally, and 5.0 km vertically. The source is centered at 9.35 km depth below main sea level and embedded in independently imaged anomalously weak crustal rocks. The source orientation appears to be controlled by the local stress field at the intersection of two major WNW‐ESE and NW‐SE striking tectonic lineaments. We derive an average volumetric strain rate of 8.4 × 10−12 s−1 by transcrustal pressurization which may have contributed to flank instability and mass wasting events in the southern and eastern sectors of the island.Natural Environment Research Council (NERC)European Union FP

The Influence of Viscoelastic Crustal Rheologies on Volcanic Ground Deformation: Insights from Models of Pressure and Volume Change

This is the final version. Avaialble on open access from Wiley via the DOI in this recordInelastic rheological behaviour, such as viscoelasticity, is increasingly utilised in the modelling of volcanic ground deformation, as elevated thermal regimes induced by magmatic systems may necessitate the use of a mechanical model containing a component of time-dependent viscous behaviour. For the modelling of a given amplitude and footprint of ground deformation, incorporating a viscoelastic regime has been shown to reduce the magma reservoir overpressure requirements suggested by elastic models. This phenomenon, however, is restricted to pressure-based analyses and the associated creep behaviour. Viscoelastic materials exhibit additional constitutive time-dependent behaviours, determined by the stress and strain states, that are yet to be analysed in the context of volcanic ground deformation. By utilising a mechanically homogeneous model-space and distinct reservoir evolutions, we provide a comparison of three viscoelastic rheological models, including the commonly implemented Maxwell and Standard Linear Solid configurations, and their time-dependent behaviours from a fundamental perspective. We also investigate the differences between deformation timeseries resulting from a pressurisation or volume change; two contrasting approaches that are assumed to be equivalent through elastic modelling. Our results illustrate that the perceived influence of viscoelasticity is dependent on the mode of deformation, with stress-based pressurisation models imparting enhanced deformation relative to the elastic models, thus reducing pressure requirements. Strain-based volumetric models, however, exhibit reduced levels of deformation and may produce episodes of apparent ground subsidence induced by source inflation or vice versa, due to the relaxation of crustal stresses, dependent on whether the reservoir is modelled to be expanding or contracting, respectively.Natural Environment Research Council (NERC