Abstract

Collapse of shallow magma chamber roofs and formation of collapse calderas are commonly accompanied by ejection of enormous volumes of pyroclastic material to the atmosphere and thus represent severe natural hazards. Numerical analysis can help researchers in understanding the conditions, when these phenomena may occur.

The main objective of the present paper is to find a suitable approach to finite element simulation of shallow magma chambers and roof collapse. The model has to capture the dominant mechanical phenomena, such as interaction of the host rock with magma and progressive failure of the chamber roof To this end a comparative study, which involves various representations of magma (inviscid fluid, nearly incompressible elastic or plastic solid) and constitutive models of the host rock (fracture, plasticity), is carried out.

The most promising results are obtained with the quasi-brittle fracture model of rock, which correctly captures formation of tension-induced radial and circumferential fractures during magma injection to the chamber. Subsequent magma withdrawal from the chamber results in collapse of the chamber roof.

While most previous studies of caldera collapse cited in the literature rely on elastic stress analysis, the proposed approach advances modeling of the process by incorporating nonlinear failure phenomena and nearly incompressible behavior of magma. This leads to a more realistic representation of roof collapse, which is consistent with field observations.

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