Answer:
Subduction zones form at places where two plates collide and one of them moves below the other.
Step-by-step explanation:
Subduction zones form only at one of the three types of plate boundaries, at convergent plate boundaries. At this type of plate boundary, we have tectonic plates that move toward each other, thus they collide. The plate that is situated lower and is denser, or is much smaller, moves below the plate that is situated higher and is less dense or is significantly larger.
As one of the plates starts to gradually move below the other, its crust gets into the mantle where it is melted and recycled. On the plate that remains on top, the crust is getting lifted up near the plate boundary so mountain ranges form. The subduction zone, if in the ocean, is characterized by oceanic trench and high volcanic activity, while if on land, mountain ranges rise above it, with earthquakes being present but there is a lack of volcanic activity.