How are the convectional currents in the mantle initiated and maintained?
Convectional currents in the mantle are initiated due to radioactive elements causing thermal differences in the mantle portion. The heat within the earth comes from two main sources: radioactive decay and residual heat.
These currents are maintained through a continuous cycle known as a convection cell. The heated material rises to the surface, spreads, and begins to cool. Subsequently, it sinks back into deeper depths. This cycle is repeated over and over to generate convective flow, which acts as the force for plate movement.
Explanation
The answer is derived from the section 'Convectional Current Theory' and 'Force for the Plate Movement'. It identifies the initiation cause as radioactive elements creating thermal differences (Arthur Holmes' theory) and lists the heat sources. It explains the maintenance of currents through the cyclical process of rising, spreading, cooling, and sinking, forming a convection cell.