Effect of different rock density profiles on magma ascent and on the statistical distribution of simulated eruptions

The structure of a volcanic edifice depends on composition, volume of erupted magma, and mechanism of eruption. In particular, pressure variations with depth due to density variations of the volcanic rocks are crucial for magma degassing processes as well as buoyancy mechanisms. In this paper, we analyze the effects of three different pressure profiles with depth on the probability of occurrence of simulated eruptive events. We describe the dynamics of magma ascent by means of a time dependent Self-Organized-Criticality field, which controls the opening of crack networks through which discrete magma batches are allowed to rise. We find a characteristic power-law behavior for the number of eruptions with erupted volume in all considered cases. As concerns the probability of occurrence of an eruptive event with a given percentage of gas losses, we find that extreme events, i.e., events with the lowest percentage of gas losses, are more likely to occur if a step function is used to describe the relationship between rock density and depth.