Rigidly moving continental and oceanic plates with distinct thermal and mechanical properties, and finite thickness, are included in a two-dimensional numerical model of mantle convection. Model plates typically span six vertical increments of a finite difference mesh. We model two identical continents being carried towards each other by a pair of underlying, counter-rotating, mantle convection cells. Upon meeting at the model mid-plane the model continents form a motionless, rigid, conducting, ''supercontinent'' along a portion of the upper boundary, while the model oceanic plates continue to move and recycle through the mantle. The resulting changes in the mechanical boundary conditions at the upper surface prove to be important factors in facilitating flow reversal below the supercontinent, leading to a subsequent dispersal of the individual continental blocks. We find the following factors to favor the development of sustained flow reversal below our model supercontinent: wider continents, lower thermal diffusivity of continental plates, thicker plates and lower proportions of internal radiogenic heating within the mantle. ¿ American Geophysical Union 1993