1. Plate Tectonics

2. Theory of Plate Tectonics
A combination of two other theories:
1. Continental Drift
2. Sea Floor Spreading

3. Convection
Process by which currents are driven by temperature differences within fluid bodies.
When a fluid is heated, it expands, lowering the density of the heated material, causing it to rise through the cooler fluid.
As it rises it will cool, becoming more dense (because it is cooler) than the surrounding fluid. It will then begin to sink.

4. Convection Currents
This behavior sets up convection currents in the mantle that cause plate movement.
Convection Video

5. Plate Tectonics
States that Earth’s lithosphere is broken into slabs called plates, that move in different directions and rates.

6. Plate edges can be drawn by connecting the dots that mark earthquakes’ epicenters.

7. Plates can be made of : All Oceanic Lithosphere
All Continental Lithosphere
Nearly all are made of a combination of both.

8. Plate Boundaries Are the edges where two plates meet.
Most Geologic activity (volcanoes, earthquakes, mountain building) take place on plate boundaries.

9. 3 Types of Plate Boundaries:
1. Divergent
2. Convergent
3. Transform
The type of plate boundary and type of crust for each side determines the geologic activity that will be found there.

10. Divergent Boundaries Plates move away from each other.
Most occur at mid-ocean ridges
Primarily responsible for
sea-floor spreading

12. Rift valley –
divergent plate movement that occurs on land by the pulling apart of a continent

13. Convergent Boundaries
Plates move towards each other.
3 types
1. Oceanic + Oceanic
2. Oceanic + Continental
3. Continental + Continental

14. Oceanic + Oceanic
Subduction: One plate is pushed under the other plate.
Can form a deep sea trench: plate descends to mantle & melts.
Can form Island Arc if formed magma is pushed back to surface.
Ex. Aleutian
Islands of Alaska
Subduction Video

15. Ex. Aleutian
Islands of Alaska

16. Oceanic + Continental
Subduction of oceanic crust forms mountain ranges with volcanoes.
Trenches, Volcanoes, Earthquakes

17. Oceanic + Continental
Ex. Peru-Chile Trench

18. Continental + Continental
Forms high mountain ranges.
No Volcanoes because of thick crust.
Large Earthquakes

19. Continental + Continental
Ex. Himalayas

20. Continental + Continental

21. Transform Boundaries
Plates move past each other in opposite directions
Crust is deformed or fractured
Massive earthquakes

22. Transform Boundaries
Ex. San Andreas Fault

23. Intraplate Activity
Geologic activity that takes place within a plate rather than at plate boundaries.
A mantle plume of hot rock rises up from near the core-mantle boundary through the crust to the surface to form a hotspot.

24. Ex. Hawaiian Islands

25. The tectonic plate moves over a fixed hotspot forming a chain of volcanoes.
The volcanoes get younger from one end to the other.
Hotspot Volcano Video

27. Past locations of the hotspot in millions of years.

29. Review What are the 3 Types of Plate Boundaries?
What are the 3 Types of Convergent Boundaries?
What intraplate activity is responsible for the Hawiian islands?

30. Review Give an example of: a Divergent Boundary. a Transform Boundary.
Oceanic-Oceanic Convergent.
Oceanic-Continental Convergent.
Continental-Continental Convergent.