The Role of Tectonic Stress in Triggering Large Silicic Caldera Eruptions

Abstract

We utilize 3-D temperature-dependent viscoelastic finite element models to investigate the mechanical response of the host rock supporting large caldera-size magma reservoirs (volumes >10 2 km 3 ) to local tectonic stresses. The mechanical stability of the host rock is used to determine the maximum predicted repose intervals and magma flux rates that systems may experience before successive eruption is triggered. Numerical results indicate that regional extension decreases the stability of the roof rock overlying a magma reservoir, thereby promoting early-onset caldera collapse. Alternatively, moderate amounts of compression (≤10 mm/year) on relatively short timescales (<10 4 years) increases roof rock stability. In addition to quantifying the affect of tectonic stresses on reservoir stability, our models indicate that the process of rejuvenation and mechanical failure is likely to take place over short time periods of hundreds to thousands of years. These findings support the short preeruption melt accumulation timescales indicated by U series disequilibrium studies.Plain Language Summary Catastrophic caldera-forming volcanoes, often referred to as "supervolcanoes," are one of the greatest natural hazards on Earth. Understanding how these explosive eruptions are triggered is critical for forecasting volcanic activity at the world's largest volcanoes and mitigating their hazards. Using sophisticated numerical models, the affect of plate tectonic stress is investigated to determine its role in triggering large caldera-forming eruptions. The numerical experiments indicate that calderas located in extensional tectonic settings erupt more readily than calderas located in compressional settings or in tectonically neutral settings. Additionally, calderas in extensional settings fail on shorter timescales than calderas located in compressional or tectonically neutral settings. The most important outcome of this work is that our numerical models show for the first time that the rock surrounding a large magma reservoir is only stable on timescales of centuries to thousands of years when new magma is actively being injected into the magma reservoir. This finding provides important constraints on the amount of time necessary to recharge and erupt a large, supervolcano size reservoir from the first indication of magmatic activity.

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

“…This can be carried out with models specific to volcanic systems containing heterogeneous crustal properties, provided by seismic tomography, spatially variable rheological effects through the use of viscoelastic shells within an elastic medium (e.g., Currenti, ; Currenti & Williams, ; Delgado et al, ; Newman et al, ; Segall, ), or a temperature‐dependent viscosity distribution that accounts for crustal geotherms and the perturbation owing to a modeled magmatic source (Del Negro et al, ; Gottsmann et al, ; Gottsmann & Odbert, ; Gregg et al, ; Hickey et al, ). Further to this, an important consideration is the influence of regional stresses and strain fields (Costa et al, ; Currenti & Williams, ), such as active extension within the Taupo Volcanic Zone (e.g., Cabaniss et al, ), on the observed viscoelastic behaviors and the resultant deformation time series.…”

Triggering of eruptions at Axial Seamount, Juan de Fuca Ridge

“…We utilize this twenty-two-year record of deformation to constrain 3D finite element models which hindcast the 2011 and 2015 eruptions of Axial Seamount. In particular, we expand upon the approach of Cabaniss et al 18 and use the COMSOL Multiphysics 5.4 modeling software to calculate stress and strain in the modeled host rock surrounding the expanding Axial magma reservoir, which is modeled as a pressurized void filled with an idealized fluid. The geometry of the simulated reservoir is approximated from a previously identified region of high melt fraction within the body of the main magma reservoir (MMR) at Axial Seamount 28,29 .…”

“…www.nature.com/scientificreports www.nature.com/scientificreports/ void space from which volumetric change and flux rate required to reproduce the observed deformation at the seafloor are estimated. As in Cabaniss et al 18 , Mohr-Coulomb and tensile failure are calculated throughout the model space along with Andersonian stress orientations 30 to determine fault type and orientation in regions where failure is calculated. For this study, eruption is defined as the first occurrence of tensile failure at the magma reservoir boundary coincident with through-going Mohr-Coulomb failure (effectively linking the reservoir to the surface).…”

“…Furthermore, the ductile nature of rock surrounding a hot magma reservoir is likely to buffer the system from mechanical failure. Some numerical findings suggest that eruptions are triggered when conditions www.nature.com/scientificreports www.nature.com/scientificreports/ of critical stress, induced by external phenomena such as tectonic stresses or large earthquakes, occur in the host rock supporting a magma reservoir 18,19 .…”

How Accurately Can We Model Magma Reservoir Failure With Uncertainties in Host Rock Rheology?

“…First, the relationship between failure and eruptions is unclear. Throughgoing failure which connects the magma chamber to the surface has been indicated as a potential catalyst of caldera formation eruptions (e.g., Cabaniss et al, ; Gregg et al, , ). However, large caldera eruption cycles may be much longer than thousands of years, far outside of the time scales in this investigation.…”