1. Plate Boundaries: Divergent, Convergent, and Transform
Plate Movements Part 3
Plate Boundaries: Divergent, Convergent, and Transform

2. Tectonic Plates Review
The Earth’s rigid lithosphere (crust and upper mantle) is broken into numerous plates.
The plates move around on top of the molten asthenosphere (lower mantle).
As the plates move individually, this motion means some plates move apart while others collide.
This motion is driven by the mantle’s convection currents, ridge push, and gravity pull.

3. Types of Plate Boundaries
There are three types of plate boundaries:
Divergent
Convergent
Transform
Each type of boundary produces unique features on Earth’s crust . . .

4. Divergent Boundary At a divergent boundary, 2 plates separate.
These plates create new crust from magma.
Magma pushes aside the old crust as new rocks form.
The type and magnetism of the rock makes a mirror image on both sides of the ridge.

5. Divergent Boundary Feature: Mid-Ocean Ridges
Mid-Ocean ridges occur when the divergent boundary is underwater at an oceanic-oceanic divergent boundary.
This is also the site of sea floor spreading since new material is added as the plates separate.

6. Divergent Boundary Feature: Rift Valley
Rift valleys occur when the divergent boundary is on land at a continental-continental divergent boundary.

7. Convergent Boundary At a Convergent Boundary, 2 plates collide.
The result of the collision depends on the types of crusts where the plates hit.
Oceanic crust is always denser than continental crust.
These boundaries consume crust as it subducts.

8. Convergent Boundary Feature: Subduction Zone
When the two plates collide and one is denser than the other, then the denser plate SUBDUCTS (slides under) the less dense plate.
The area where the denser plate slides underneath is called the subduction zone.

9. Convergent Boundary Feature: Trenches
Trenches form at oceanic-continental or oceanic-oceanic convergent boundaries
As the oceanic plate bends down, it leaves a gap in the sea floor.

10. Convergent Boundary Feature: Continental Volcanoes
Continental volcanoes form at oceanic-continental convergent boundaries.
The oceanic crust melts underneath the continental crust, and then magma pushes up through the continent.
Continental Volcanoes

11. Convergent Boundary Feature: Volcanic Island Arcs
Volcanic Island Arcs occur at oceanic-oceanic convergent boundaries.
The denser oceanic crust slides under less dense crust, melts, and then magma pushes up through the upper oceanic crust.

12. Convergent Boundary Feature: Mountain Ranges
Mountain Ranges form at continental-continental convergent boundaries.
Continental crust is too buoyant (not dense enough) to be pulled into the mantle, detaches from the bottom of the plate, and piles up into mountains.

13. Transform Boundary
At a Transform Boundary, 2 plates scrape past each other.
Crust is not formed or consumed at these boundaries.
Transform boundaries have numerous volcanoes and shallow earthquakes.