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Numerical simulation of caldera formation due to collapse of a magma chamber

The caldera structure after collapse of the magma chamber was estimated by numerical simulation. In the simulation, the collapse of the magma chamber was approximated by the contraction of a small sphere in the elastic medium, and the distribution of plastic and/or rupturing area was calculated using the Coulomb failure criterion under the assumption of an elastic‐perfectly‐plastic material. Given an undefined or isotropic regional stress field, the plastic area (caldera) was found to develop as a circular depression on the surface, appearing funnelform in cross section. Under an anisotropic regional stress field, the caldera developed in the direction of the maximum compression (or minimum extension) axis. In all simulations, the collapse of the magma chamber resulted in the formation of an outward dipping reverse ring fault around the area above the chamber, and an inward dipping normal ring fault at the periphery of the caldera.