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Francisco Delgado Department of Earth and Atmospheric Sciences

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.

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Francisco Delgado Department of Earth and Atmospheric Sciences

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  1. 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

  2. Volcanoes Deformation < 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.

  3. How do we study deformation in active volcanoes? InSAR

  4. Topics 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.

  5. Benchmark with Analytical Solution Z=10 km, R=2 km, ΔP = 18 MPa, G=32 GPa, n=0.25

  6. Surface unloading: changes in hoop stress Unloading = 2 MPa

  7. Surface unloading: changes in hoop stress Ts = 20 MPa

  8. Formation of eruptive vents in calderas

  9. Contact elements: Augmented Lagrangian formulation Simo 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.

  10. Contact elements: Newton Raphson

  11. Caldera Mesh E = 10 GPa, 1km, frictional contact E = 80 GPa

  12. Caldera Boundary Conditions ΔP = 126 Mpa (simulates an eruption)

  13. Does the fault slip or open?

  14. Are the displacements measurable? Ulos = 0.93Uz -0.37Ur

  15. Conclusions • 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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