Lesson 3: Convergent Boundaries

Key Idea

At a convergent boundary, two plates move toward each other and collide. If one plate is denser than the other, it cannot stay on top. Instead, it bends and slides underneath the other plate.

This downward movement is called subduction. The sinking plate descends into the hot mantle. This is a destructive process where the solid rock of the plate edge is "recycled" back into the soft, solid interior of the Earth.

Key Idea

Unlike divergent boundaries where rock is made, convergent boundaries are where rock is destroyed. As the subducting plate sinks deep into the mantle, it creates a massive amount of friction and encounters extreme heat.

The edge of the plate eventually melts or is incorporated back into the mantle material. This explains why Earth does not grow larger despite new rock being made elsewhere; the recycling of old plates balances the creation of new ones.

Key Idea

The process of subduction creates specific landforms. Where the plate bends down, a deep valley called a trench forms on the ocean floor. These are the deepest places on Earth.

Additionally, as the sinking plate heats up, it releases fluids that melt the rock above it. This magma rises to the surface to form a line of volcanoes parallel to the trench. These geologic features are the signature fingerprints of a convergent boundary.