1. Chapter 5, Lesson 1, Interactions at Plate Boundaries

2. Chapter 5, Lesson 1, Interactions at Plate Boundaries Slide 1
*What is the main idea?
______________
-What is stress and deformation?
*There are three main types of plate boundaries where stresses cause rocks to deform.
____________________________________________________
-Stress is caused when plates collide at plate boundaries.
-Sometimes rocks can bend under stress without breaking.
-Deformation occurs when rocks change shape due to high temperatures and pressure at plate boundaries.

3. Chapter 5, Lesson 1, Interactions at Plate Boundaries Slide 2
-What is stress and deformation?
(continued)
-There are two types of deformation:
Plastic deformation occurs when rocks change shape permanently by folding.
Elastic deformation occurs when rocks snap back to their original shape after stress is removed.
-A break or crack in rock is called a fracture.
-In nature, if the rocks on one side of a fracture moved relative to the rocks on the other side, the fracture is a fault.

4. Chapter 5, Lesson 1, Interactions at Plate Boundaries Slide 3
fracture
fault

5. Chapter 5, Lesson 1, Interactions at Plate Boundaries Slide 4
*What are the types of stress?
*There are three main types of stress that can cause faulting:
Tension-when two plates are moving apart, tension pulls lithosphere apart so that it stretches and becomes thinner.

6. Chapter 5, Lesson 1, Interactions at Plate Boundaries Slide 5
*What are the types of stress?
(continued)
2. Compression-Where two lithospheric plates are forced together, compression makes the rocks thicker

7. Chapter 5, Lesson 1, Interactions at Plate Boundaries Slide 6
*What are the types of stress?
(continued)
3. Shear-this occurs when rocks slide horizontally and the lithospheric plates neither thin nor thicken

8. Chapter 5, Lesson 1, Interactions at Plate Boundaries Slide 7
-What are the types of faults?
-Examining a fault helps scientists determine the stresses that caused it.
-If a fault’s surface is inclined, the block of rock above the fault is the hanging wall, and the block of rock below is the foot wall.

9. Chapter 5, Lesson 1, Interactions at Plate Boundaries Slide 8
-What are the types of faults?
(continued)
-There are three types of faults:
Normal Faults-these are faults that slope at an angle when rocks break and the hanging wall moves down the footwall.

10. Chapter 5, Lesson 1, Interactions at Plate Boundaries Slide 9
-What are the types of faults?
(continued)
2. Reverse Faults-these occur when rocks are pushed together and the hanging wall moves up the footwall.

11. Chapter 5, Lesson 1, Interactions at Plate Boundaries Slide 10
-What are the types of faults?
(continued)
3. Strike-Slip Faults-these faults occur when plates slide horizontally past each other. Strike-slip faults are vertical and not inclined, so there is no footwall or hanging wall.

12. Chapter 5, Lesson 1, Interactions at Plate Boundaries Slide 11
*What are the types of plate boundaries?
*The edges of Earth’s plate boundaries meet at plate boundaries that extend deep into the lithosphere.
*Faults form along these plate boundaries.
*Like faults there are three major types of plate boundaries:
Divergent Plate Boundaries-these are two lithospheric plates that are moving apart
*Mid-ocean ridges occur along divergent plate boundaries because as the two plates move apart, new seafloor forms.

13. Chapter 5, Lesson 1, Interactions at Plate Boundaries Slide 12
*What are the types of plate boundaries?
(continued)
*Most divergent plate boundaries are located on the seafloor, but they can also form on land when a continent is pulled apart,
*The process that pulls a continent apart is called continental rifting.
East
African
Rift

14. Chapter 5, Lesson 1, Interactions at Plate Boundaries Slide 13
*What are the types of plate boundaries?
(continued)
*Divergent plate boundaries form where tension stresses cause the lithosphere to stretch and become thinner.
*They form normal faults and as the hanging wall blocks slip down, a long, flat, narrow rift valley forms.
*The East African Rift is a rift valley where crust is being pulled apart and large slabs of rock are sinking.
*If continental rifting continues, then East Africa will eventually part from West Africa.

15. Chapter 5, Lesson 1, Interactions at Plate Boundaries Slide 14
*What are the types of plate boundaries?
(continued)
2. Convergent Plate Boundaries-They are formed when two lithospheric plates move toward each other.
*They can occur in both continental and oceanic lithosphere.
*There are three types of interactions:
Ocean to ocean-Where two oceanic plates move toward each other, and one plate sinks beneath the other.
*The process in which one plate is forced into the mantle beneath another plate is called subduction.

16. Chapter 5, Lesson 1, Interactions at Plate Boundaries Slide 15
*What are the types of plate boundaries?
(continued)
Ocean-to-ocean convergent plate boundary

17. Chapter 5, Lesson 1, Interactions at Plate Boundaries Slide 16
*What are the types of plate boundaries?
(continued)
Ocean-to-Continent-If one of the converging plates is oceanic, and the other is continental, the oceanic plate always subducts.
*This occurs because most continental rocks are less dense than oceanic rocks.

18. Chapter 5, Lesson 1, Interactions at Plate Boundaries Slide 17
*What are the types of plate boundaries?
(continued)
Continent-to-continent-When continental plates collide, neither continental plate subducts.
*This occurs because continental rocks are not dense enough to sink into the mantle.

19. Chapter 5, Lesson 1, Interactions at Plate Boundaries Slide 18
*What are the types of plate boundaries?
(continued)
3. Transform Plate Boundaries-these occur where two plates slide horizontally sideways past one another. Lithosphere is neither formed nor recycled at these plate boundaries.

20. Chapter 5, Lesson 1, Interactions at Plate Boundaries Slide 19
*What are the types of plate boundaries?
(continued)
*Oceanic transform plate boundaries connect pieces or segments of the mid-ocean ridges.
*Most oceanic transform boundaries are relatively short, but there are a few long ones.
*Continental transform plate boundaries slice through continental lithosphere as huge strike-slip faults.
*Earthquakes resulting from movement along these faults can be very destructive if they occur in populated areas.
*The San Andreas Fault in California is the best-studied continental transform plate boundary in the world.

21. Chapter 5, Lesson 1, Interactions at Plate Boundaries Slide 20
-Summary
-Stresses can cause rocks to deform and leave fractures and faults.
-Analyzing how rocks bend and break helps scientists to determine the types of stresses exerted on them.
-From these data, the direction and distance that the lithospheric plates have moved and the way that they have interacted at plate boundaries can be determined.