Modelling the rheology and cooling of lava flows

The rheological properties of lavas are of major importance in determìning the dynamìcs of lava flows. Such properties reflect the inherent structures of molten silicates and the fact that lava ìs a multiphase system. Below its liquidus temperature, lava behaves as a non-Newtonian fluid and is commonly described as a pseudoplastic fluid. A simpler model which is often used is the Bìngham fluid, characterized by a yìeld stress and a plastic viscosity. These rheological parameters depend on the composition of lava (basic or acidic) and are strongly temperature-dependent. Many other factors, including the presence of water, gas loss, crystal content and degree of polymerization, control the rheology of lava. Surface effects, such as surface tension, the strength of solid crust and ground erosion by melting, also influence flow morphology and dynamics. The roles of these factors are examined on the basis of existing studies. To better understand lava flow dynamics such factors must be investigated systematically, both theoretically and in the laboratory, supported by more accurate measurements in the field.