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Effects of regional stress state and pore fluid pressure on the onset and style of caldera collapse

Matías A. Villarroel a, b, Martin P.J. Schöpferc, John Browninga,d, Eoghan P. Holohanb, Claire E. Harnettb, Carlos J. Marquardta,d, Pamela P. Jarae

  • Affiliations: a Departamento de Ingeniería Estructural y Geotécnica, Pontificia Universidad Católica de Chile, Santiago, Chile b UCD School of Earth Sciences, University College Dublin, Dublin, Ireland

  • Presentation type: Poster

  • Presentation time: Thursday 16:30 - 18:30, Room Poster Hall

  • Poster Board Number: 54

  • Programme No: 3.11.14

  • Theme 3 > Session 11

Abstract

c Department of Geology, University of Vienna, Vienna, Austria d Departamento de Ingeniería de Minería, Pontificia Universidad Católica de Chile, Santiago, Chile *e Departamento de Ingeniería en Minas, Facultad de Ingeniería, Universidad de Santiago, Chile * Collapse calderas form when the roof of a magma chamber subsides during large-volume eruptions. Although calderas can develop in diverse tectonic settings, the role of regional ('far-field') stresses influencing the nucleation and architecture of caldera faults remains poorly understood. Additionally, while pore fluid pressure is known to reduce effective stress, it has often been overlooked in previous caldera collapse models. In this study, we use two-dimensional Distinct Element Method (DEM) models to investigate how regional stress regimes and pore fluid pressure affect the stress, strain, and faulting processes during caldera subsidence. A shallow magma chamber is modeled as an inviscid inclusion within a homogeneous crust, and magma withdrawal is simulated by reducing the chamber's pressure. Calderas forming under regional extension require only around half the amount of underpressure to trigger the onset of collapse compared to the isotropic scenario due to reduced fault friction. If the crust is also fluid-saturated, the required underpressure reduces to around 1/3. We observed three deformation stages: elastic surface subsidence, the onset of collapse, and complete roof failure. The style of faulting varies with the tectonic setting---extensional regimes favor inward-dipping normal faults, whereas compressional regimes promote outward-dipping reverse faults. These findings underscore the importance of incorporating regional stress and crustal properties into volcanic hazard assessments, particularly for caldera systems influenced by complex hydrothermal or tectonic processes. Comparisons with recent caldera collapse events (e.g., Bárdarbunga) demonstrate the utility of DEM modelling for understanding crustal responses to magma withdrawal.