A mathematical model is considered for Rayleigh-Benard convection of
mantle whose viscosity depends strongly both on temperature and pressure
defined in an Arrhenius form. The model is solved numerically for
extremely large viscosity variations across a unit aspect ratio cell,
and steady solutions are obtained. To improve the efficiency of
numerical computation, a modified viscosity law with a low temperature
cut-off is used. The aim is to investigate the convection pattern with
internal heating at a very high viscosity variation in the presence of
high Rayleigh number. The study also investigates the relation between
temperature-dependent parameter and pressure dependent parameter. The
numerical simulation is done using the finite element method based PDE
solver and the results are presented through figures, tables and graphs.