In this paper, the classical Rayleigh–Bénard convection model is considered and solved
numerically for extremely large viscosity variations (i.e., up to 1030 ) across the mantle at
a high Rayleigh number. The Arrhenius form of viscosity is defined as a cut-off viscosity
function. The effects of viscosity variation and viscous dissipation on convection with
temperature-dependent viscosity and also temperature- and pressure-dependent viscosity
are shown through the figures of temperature profiles and streamline contours.
The values of Nusselt number and root mean square velocity indicate that the convection
becomes significantly weak as viscosity variation and viscous dissipation are
increased at a fixed pressure dependence parameter