The submarine volcano Axial Seamount has exhibited an inflation predictable eruption cycle, which allowed for the successful forecast of its 2015 eruption. However, the exact triggering mechanism of its eruptions remains ambiguous. The inflation predictable eruption pattern suggests a magma reservoir pressure threshold at which eruptions occur, and as such, an overpressure eruption triggering mechanism. However, recent models of volcano unrest suggest that eruptions are triggered when conditions of critical stress are achieved in the host rock surrounding a magma reservoir. We test hypotheses of eruption triggering using 3-dimensional finite element models which track stress evolution and mechanical failure in the host rock surrounding the Axial magma reservoir. In addition, we provide an assessment of model sensitivity to various temperature and non-temperature-dependent rheologies and external tectonic stresses. In this way, we assess the contribution of these conditions to volcanic deformation, crustal stress evolution, and eruption forecasts. We conclude that model rheology significantly impacts the predicted timing of through-going failure and eruption. Models consistently predict eruption at a reservoir pressure threshold of 12–14 MPa regardless of assumed model rheology, lending support to the interpretation that eruptions at Axial Seamount are triggered by reservoir overpressurization.

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.

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