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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.

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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
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.

topics to be addressed
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.
benchmark with analytical solution
Benchmark with Analytical Solution

Z=10 km, R=2 km, ΔP = 18 MPa, G=32 GPa, n=0.25

contact elements augmented lagrangian formulation
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.

caldera mesh
Caldera Mesh

E = 10 GPa, 1km, frictional contact

E = 80 GPa

caldera boundary conditions
Caldera Boundary Conditions

ΔP = 126 Mpa (simulates an eruption)

conclusions
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.