Pressure and Temperature Dependence of Viscosity of Volcanic Lava

We consider a model of viscosity η of volcanic lavas. The equation, describes with high accuracy the existing experimental data on temperature and pressure dependence of viscosity of igneous materials. It is demonstrated that, the activation energy E(Tg) can be expressed through the glass transition temperature Tgo. The dependencies of the parameters of the viscosity equation are discussed for most of geoscientifically relevant systems. According to the model viscosity of lava depends on the depth inside the Earth through the temperature and pressure. Therefore, the viscosity of lava at the surface could be both lower and higher the one in the bowels of the earth, depending on the composition. This is of major importance for the volcano erruptions.