Plate Boundaries

Earth’s crust plus the upper mantle forms the lithosphere.

Earth’s lithosphere is broken in a number of different pieces.

How these pieces move and interact is what plate tectonics is all about.

Convergent boundaries

• When 2 plates collide with one another.

Convergent boundaries

• When oceanic plates collide, one subducts under the other.

• This forms a valley in the ocean floor called a trench.

An example of a trench is the Marianas Trench.

Convergent boundaries

When continental plates collide mountains form.

Convergent boundaries

• What happens if an oceanic plate and a continental plate collide?

• Which plate would subduct?

• The oceanic plate must subduct under the continental plate.

• A continental plate is simply too buoyant to subduct under an oceanic plate.

Divergent boundariesA divergent boundary is the line between two

plates where they are moving apart.

Divergent boundaries

• Divergent boundaries can be found on continents as rift valleys.

• When a rift valley forms on land, it may eventually split the landmass.

Divergent boundaries

• Divergent boundaries can also be found in the ocean

• Sea floor spreading occurs at a mid ocean ridge.

Plate boundaries

• An edge of a lithospheric plate that slides by another plate is called a transform fault boundary.

Transform fault boundaries• When seen from

above, the feature will appear to make a zig-zag.

• Causes Earthquakes

• San Andreas Fault

Earth’s lithospheric plates• Can you identify the three types of plate

boundaries labeled A, B, and C?.