Cavitation development in a viscous compressed magma at explosive eruption of volcanoes

It is well known that a compressed magma contains enough large amount of dissolved water (up to 5-7% of weight fraction). During eruption under decompression wave a magma becomes supersaturated. Dissolved gas comes out from solution forming a separate phase (bubbles). If the liquid magma has a high viscosity, the gas is not able to expand very easily, pressure is increasing inside of bubbles, and they burst explosively fragmenting a liquid magma into clots. The solidified clots become bombs or volcanic ash. Development of these processes, as was proved, depends on four factors: an amount of gas dissolved in a magma, a viscosity of magma, the rate of magma decompression and the number of nucleation sites. The paper presents the full system of the equations for the study of the initial stage of explosive eruption based on the kinetic theory of phase transformations. The problem of nucleation frequency in a liquid magma as well as the dynamics of cavitation development was numerically studied, taking into account the gravity, special model of diffusive zones and dynamically changing viscosity.