Silicate Melt Properties and Volcanic Eruptions

[1] Knowledge about the properties of silicate melts is needed by volcanologists and petrologists to evaluate the dynamics of volcanic eruptions and magmatic processes. These properties include the solubility and diffusivity of volatile components in silicate melts, silicate melt viscosity, and the fragmentation condition. Data and models of each property are reviewed and assessed. For rhyolitic melts many properties are sufficiently well known to allow realistic modeling of volcanic and magmatic processes. One interesting example is the role of speciation in the solubility and diffusivity of H2O and CO2. Even though both H2O and CO2 are present in silicate melts as at least two species, the complexity in the solubility and diffusion behavior of H2O and the simplicity of CO2 are due to differences in the speciation reaction: For the H2O component the stoichiometric coefficient is one for one hydrous species (molecular H2O) but is two for the other hydrous species (OH) in the species interconversion reaction, whereas for CO2 the stoichiometric coefficients for all carbon species are one. The investigation of the species reaction not only helps in understanding the solubility and diffusion behavior, but the reaction among the hydrous species also serves as a geospeedometer (cooling rate indicator) for hydrous rhyolitic pyroclasts and glass and provides a method to infer viscosity. For melts other than rhyolite, a preliminary description of their properties is also available, but much more experimental and modeling work is necessary to quantify these properties more accurately.