Abstract
Volcanoes usually show signs of unrest before an eruption. Establishing physical controls on the duration of precursory activity, that is run-up time, could improve understanding of the dynamics of magma ascent from a shallow magma reservoir to the surface. Another observable indicative of eruption dynamics is the interevent repose time, that is, the time between magmatic eruptions. The repose time could be associated with the mechanism that recharges the magmatic system. Both of these quantities depend on magma viscosity and hence magma composition in addition to other factors. In this work we investigate the interrelationship between run-up time, repose time and silica content by compiling a database of 73 magmatic eruptions from 34 different volcanoes around the world. Run-up and repose time are correlated with similar to 40 per cent of the variance in the data well explained by a linear correlation. Both of these quantities are significantly correlated with silica content, but although repose times and silica content are highly correlated, run-up times show a weaker correlation with silica content. The data range from basaltic to dacitic with a preponderance of low silica eruptions, so we can investigate the gross influence of viscosity in controlling both run-up and repose time. We also investigate the role of volume erupted finding repose times correlated with the erupted volumes. The trends are clearest when comparing a large range of silica on the global data set and appear to be obscured by other processes for subsets that cover only a small range of silica contents. High silica, and thus by inference high viscosity, systems have longer repose and run-up times and tend to erupt larger quantities of material. The observed interrelationships can provide new insights for constraining physical and probabilistic models for volcanic hazard mitigation.