Some consequences of volcanic edifice destruction for eruption conditions
Résumé
Destruction of a volcanic edifice by landslides or phreatic explosions unloads the upper crust. Induced changes of stress field around, and of magmatic pressure within, a magma reservoir are investigated with an analytical model for the deformation of a liquid-filled cavity within an elastic half-space. Unloading affects the reservoir pressure, and hence the net result depends on how the liquid-filled reservoir responds to a change of remote stress. Magma compressibility is taken into account and may dampen changes of internal pressure in small volatile-rich reservoirs. The main consequence of edifice destruction is a decrease of magmatic pressure and stresses on the reservoir walls. In some cases, this may be responsible for dyke closure at the reservoir walls, which stops magma withdrawal and may prevent eruption. If an eruption does occur, edifice destruction affects the volume of magma erupted. Depending on edifice size, magma reservoir size and depth, the erupted volume may be smaller or larger than that which would be erupted with no damage to the edifice. These results suggest that major phreatic explosions may prevent magmatic eruptions.