Convection currents within the Earth's mantle are driven by the uneven heating of the mantle material. Warmer areas of the mantle become less dense and rise towards the Earth's crust, while cooler areas become denser and sink back down towards the core.
Question One:
When magma is heated within the mantle, the temperature of the magma increases, which causes it to expand and become lighter or less dense compared to the surrounding material. As a result, the heated magma rises towards the surface. This movement occurs because the less dense magma is buoyed up by the denser, cooler mantle material surrounding it.
Question Two:
When magma is cooled within the mantle, its temperature decreases, leading to an increase in density as the material contracts. As the magma becomes denser than the surrounding mantle, it sinks back down towards the deeper layers of the mantle. This creates a cycle of movement as the cooler, denser material moves down, making room for warmer, less dense magma to rise, thus perpetuating the convection currents.