Final answer:
At convergent plate boundaries, when one heavier tectonic plate pushes over and forces another one to move down, it is a process called subduction. The denser and heavier plate is forced beneath the other plate and into the upper mantle.
Step-by-step explanation:
When one heavier tectonic plate pushes over and forces another one to move down, it is a process that occurs at convergent plate boundaries. In this type of boundary, plates are moving toward each other. The plate that is denser and heavier will be forced beneath the other plate in a process called subduction. This subduction zone is marked by an ocean trench and the subducted plate is forced into the upper mantle, eventually melting several hundred kilometers below the surface.