GAS EVOLUTION-GENERATED PRESSURE RISE IN MAGMA CHAMBERS AND SEISMICITY OF VOLCANOES

Abstract

The occurrence of gas bubbles at depths of 10 to 15 km or more has been demonstrated by analysis of inclusions. The ascent of gas bubbles in a closed isochoric magma system generates in them an excess (greater than in the host rock) pressure. Fracture results in generation or propagation of cracks, which increases the volume of the magma system. This allows the gas in the system either to expand or to evolve from the magma, with a resultant drop in pressure in the system. We analyze the equations defining the change in pressure in the magma vent of a volcano as a result of the gas evolution-generated pressure rise (GEGPR) to find out whether these equations fit the observed variations in the seismic regime prior to volcano eruptions.