1. L 5.1 Interactions at Plate Boundaries
By the end of this lesson, you should be able to:
-describe types of stress that deform rock
-explain the relationship between geologic features of Earth’s surface to types of plate boundaries

2. Compare and contrast this picture to plate tectonics.

3. Look for these KEY words throughout the lesson:
Fracture Compression Fault Tension Divergent plate boundary Shear Continental rifting Incline fault Rift valley Strike-slip fault Convergent plate boundary Normal fault Subduction Reverse fault Transform plate boundary Hanging wall Plastic deformation Footwall Elastic deformation

4. A. Stress and Deformation
Stress and deformation occur when lithospheric plates collide at plate boundaries. Earth’s plates move very slowly. Earth’s plates move at different speeds.

5. Deforming Rocks
Rocks can bend without breaking!

6. Plastic deformation: rocks change permanently shape at high temperatures and stress. They actually fold!
Elastic deformation: rocks snap back to their original shape after tension is removed.
Fracture: a break or crack in a rock.
Fault: results if the rock on one side of the fracture surface moves relative to the rock on the other side.

7. San Andreas Fault Line

8. Types of Stress Three main types of “stress” can cause faulting.
Tension
Compression
Shear

9. Tension stress occurs when two plates pull apart causing the lithosphere to stretch and it becomes thin.

10. Compression occurs when two plates are squeezed or pushed together
Compression occurs when two plates are squeezed or pushed together. This causes the lithospheric plate to bulge. This stress is caused by force.

11. Shearing occurs when two plates are pushed in opposite directions
Shearing occurs when two plates are pushed in opposite directions. The lithospheric plate may change in two different directions but it does not change the thickness of the plate.

12. BRAIN BREAK!

13. B. Types of Faults
Geologists measure the angle of the fault’s surface to figure out which way the broken sections of rock have moved.
There are 3 types of faults:
Normal
Reverse
Strike-slip

14. Inclined Fault
There is a hanging wall and a footwall in an inclined fault.
The hanging wall
is the block of rock
that lies above the
fault line.
The footwall is the
block of rock that lies below the fault line.

15. Normal Fault
Tension forces inside the Earth PULL APART rock, producing normal faults.
This kind of fault slopes at an angle.
When rocks break and slide along the fault, the hanging wall SLIDES DOWN the footwall.

16. Reverse Fault
In areas where rocks are PUSHED together, COMPRESSION produces reverse faults.
In a reverse fault, the hanging wall is pushed upward, above the footwall.

17. Strike-Slip Faults
Where plates slide past each other, SHEARING stresses produce strike-slip faults.
Instead of up and down, the plates slide past each other sideways, or horizontally.

18. BRAIN BREAK!

19. C. Types of Plate Boundaries
Plate boundaries are classified by the way rocks on either side move.
There are 3 main types of plate boundaries:
Divergent
Convergent
Transform

21. Divergent Plate Boundary
When two plates of the lithosphere are moving apart it is called a divergent plate boundary.
Mid-ocean ridges occur along the divergent plate boundary.

22. Mid-Ocean Ridges (divergent)
Hot magma, dense material below Earth’s crust is forced upward at the ridges.
New seafloor forms as two plates of the lithosphere move apart.
Seafloor located farther from a divergent plate boundary is deeper because it cools and becomes denser as it moves away from the center of the ridge.

23. Divergent Plate Boundary
Most divergent plate boundaries occur on the seafloor. Sometimes they are found on land.
When divergent plate boundaries are found on land, the land separates. It is called continental rifting.

25. Continental Rifting (divergent)
A long, narrow rift valley forms when a hanging wall slips down.
Sediment collects on the floor of the rift valley, pushing the valley deeper.
The East African Rift and the Gulf of California are examples of modern continental rift valleys.

26. Convergent Plate Boundaries
A convergent plate boundary is formed when two lithospheric plates move toward each other.
Interactions between the two plates depend upon whether the plates are continental or oceanic.
There are three types of outcomes:
Ocean to ocean
Ocean to continent
Continent to continent

27. Convergent Plate Boundaries
Where two oceanic plates move toward each other, one of the plates sinks beneath the other plate and is forced down into the mantle in a process called subduction.
The colder, older, denser slab is usually forced down into the mantle, forming a trench on the seafloor where it bends.
High temperature and pressures in the mantle release water from minerals in the slab.
Water rises from the mantle and causes rocks to melt and magma rises to the surface, forming volcanoes.

29. Convergent Plate Boundaries
Sometimes oceanic plate and a continental plate collide at a convergent boundary.
The oceanic plate always subducts because continental rocks are less dense than oceanic rocks.
The melting of subducted rock produces a curved string of volcanoes along the leading edge of the continent.

31. Convergent Plate Boundaries
When two continental plates collide, compression stress forces crust to rise and from mountains.

32. Transform Plate Boundaries
A transform plate boundary exists where two plates slide sideways past one another, eventually causing earthquakes.
Lithosphere is neither formed nor recycled at these boundaries.
Oceanic transform boundaries connect pieces or segments of the mid-ocean ridges.

33. Transform Plate Boundaries
Continental transform boundaries slice through continental lithosphere.
Large earthquakes resulting from movement along these faults can be destructive if they occur in a populated area.
The San Andreas Fault in California is the best studied continental transform boundary in the WORLD!
Most of California is on the continental North American plate. But a small part of CA, west of the SA fault lies on the adjacent Pacific plate.

34. Do you know what plate we live on?