Francisco Delgado Department of Earth and Atmospheric Sciences

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Eruptive vents formation and surface unloading in active volcanoes: insights from axis-symmetric 2D finite element models. Francisco Delgado Department of Earth and Atmospheric Sciences. Volcanoes.
Eruptive vents formation and surface unloading in active volcanoes: insights from axis-symmetric 2D finite element modelsFrancisco DelgadoDepartment of Earth and Atmospheric SciencesVolcanoesDeformation < 0.5 m over scales of ˜10-20 km: infinitesimal strain is valid. If deformation is not time dependent and source is above brittle ductile transition (˜10-15 km), linear elasticity is used → stress.How do we study deformation in active volcanoes? InSARTopics to be Addressed
  • Benchmark FEM with linear elasticity analytical solution (Mogi model).
  • Changes in hoop stress in deep chambers related to unloading.
  • Generation of eruptive vents in pre existing discontinuities.
  • Benchmark with Analytical SolutionZ=10 km, R=2 km, ΔP = 18 MPa, G=32 GPa, n=0.25Surface unloading: changes in hoop stressUnloading = 2 MPaSurface unloading: changes in hoop stressTs = 20 MPaFormation of eruptive vents in calderasContact elements: Augmented Lagrangian formulationSimo and Laursen, 1992.In the Augmented Lagrangian method the Lagrange multiplier is a fixed current estimate of the correct multiplier and is updated with each iteration of the method until g(x)<= tolerance, εN is as large as possible. Contact elements: Newton RaphsonCaldera MeshE = 10 GPa, 1km, frictional contactE = 80 GPaCaldera Boundary ConditionsΔP = 126 Mpa (simulates an eruption)Does the fault slip or open?Are the displacements measurable?Ulos = 0.93Uz -0.37UrConclusions
  • ANSYS can properly model linear elastic analytic solutions widely used in volcanology.
  • Hoop stress changes produced by unloading are very small in deep chambers: require other mechanisms to trigger eruptions.
  • Co eruptive inflation can open caldera ring faults by several centimeters. However, near field measurements are required to detect them.
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