Mechanical behaviour of volcanic edifices

Numerical modeling is used to characterize :
– the stability of volcanic edifices and magma storage zones (condition for caldera formation) ;
– the edifice rheology, the role of the edifice in the crust/edifice and magma/edifice interaction ;
– the stress field during magma transfer ;
– the consequences of a given external perturbation (edifice collapse, surface unloading due to glacier retreat…) on a magma storage zone (resulting deformation, seismicity, evolution of the stability) ;
– the consequences of magmatic injections in a detachment level on volcano stability.

Figure 1 : Evolution of the erupted volume of magma following the removal of the upper 20% of a conical edifice with a slope of 30°. Results are presented as a function of the reservoir and edifice radius. Calculations are performed for a spherical reservoir filled with incompressible magma. Crustal Poisson’s ratio is equal to 0.25. Three different values for depth to the top of the magma reservoir are considered : a) 0.5 km depth, b) 1 km depth, and c) 3 km. (from Pinel & Albino 2013.

Figure 2 : Edifice/crust interaction in the case of the large hawaiian volcanoes (Mauna Loa and Kilauea). Edifices are represented by dense and elastic cores (Young’s modulus 100 GPa, Poisson’s ratio 0,25, density 2900 kg/m3) and a light elasto-plastic cover (Young’s modulus 60 GPa, Poisson’s ratio 0,25, cohesion 1 MPa, friction angle 15°, density 2600 kg/m3) . Elastic parameters are deduced from seismic tomography, plastic parameters result from tests on rock samples issued from deep drillings in the Kilauea volcano. The décollement plane is represented by an interface with a Coulomb friction law (friction angle 10°). Oceanic crust is represented by an elasto-plastic material (Young’s modulus 100 GPa, Poisson’s ratio 0,25, cohesion 1 MPa, friction angle 15°, density 2900 kg/m3) . Effective plastic strain (norm of the deviatoric plastic strain tensor) is represented by colours (from Got et al., 2008).