Article,
Silicate melt properties and volcanic eruptions
Reviews of Geophysics, 45 (4): RG4004+ (Dec 5, 2007)
DOI: 10.1029/2006RG000216
Abstract
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.
