Theory of Plate Tectonics…

1. Theory of Plate Tectonics… • Plate Tectonics refers to the movements of plates (large segments of continents and ocean) around the Earth’s surface. • These land masses are seen as a giant jigsaw puzzle, and any one mass can’t move without creating gaps between or overlaps with other pieces • They move on the Lithospheric plates on the Liquid Mantle and move along by convection currents in the magma.

3. Check out the Theory of Plate Tectonics… click on the pic.

4. Mountains in red, volcanoes and Earthquakes in yellow…

5. Ring of Fire

6. Why is the Ring of Fire so Active? • The ring of Fire is a Ring around the Pacific ocean (on the edges of the Pacific tectonic plate) where there are numerous volcanoes and Earthquakes. • Why???...There are 7 other plates that meet the edges of the Pacific plate there– so there is lots of jostling, smashing, and moving where all the edges meet.

8. Plate Boundaries… • At the edges of the plates is where all the action occurs because of all the jostling that takes place • When Plates move – there are only 3 choices they have… • 1) crash directly into each other and one goes under the other • 2) separate from each other • 3)slide past/along one another

9. Scaffolding everything: The Ring of FIRE!

10. 3 Types of Plate Boundaries 1)DIVERGENT boundaries • 2 plates move away from each other opening a gap called a spreading center • Sometimes, molten rock rises to the Earth’s surface in the trench and this area is called a HOT SPOT

11. As molten rock comes up through the trench created by the diverging plates, it pushes the old crust aside causing it to buckle. • This process is called RIDGE PUSH

12. This is the symbol on a map for divergent boundaries Divergent… HOT SPOT RIDGE PUSH

13. Divergent plates over water… • When tectonic plates diverge over water, the spreading center is called spreading ridge or oceanic ridge. • Because the magma rising up through the trench and pushes the old crust aside, new sea floor is created • This is called SEA FLOOR SPREADING

14. The Mid Atlantic Ridge is formed by Diverging Plates • It is an area in the middle of the Atlantic ocean that is forming an ocean ridge • Sea floor spreading

15. Divergent plates over land… • When tectonic plates diverge, pull apart, over land, the spreading center is called a rift valley. • This is less common than spreading over water

16. Diverging plates in eastern Africa are slowly breaking Africa into pieces creating rift valleys at the spreading centers

17. Here’s what the rift valley actually looks like

18. 2) CONVERGENT Boundaries • When 2 plates move toward each-other • When they collide, they push on each other and one plate dives under the other. The one that dives under is the more dense (heavier) plate. • The process of one plate diving under the other is called SUBDUCTION. • Places where you find subduction are called Subduction zones.

19. Convergent Plates…

20. When Subduction occurs – the edge of the plate subducts deep into the mantle and starts to melt creating magma. That magma can make it’s way up through cracks in the crust and form volcanoes. • When the plate subducts, it “pulls” the rest of the plate with it - This is called Slab pull ( the whole slab is pulled under the other slab) • This slab pull helps keep the tectonic plates in motion.

21. Subduction, Ridge push, and Slab pull

22. Oceanic-Continental Plate Convergence… • When a dense (heavier) oceanic plate collides with a less-dense (lighter) continental plate, the oceanic plate subducts. • This creates a deep underwater valley called a trench. • As the subducting plate moves deeper, it starts to melt and magma can work it’s way to the surface forming cone-shaped Volcanoes • A chain of volcanoes = Volcanic belt • This force of collision between the 2 plates creates mountain ranges as the continental rock crumbles and folds

23. Symbol for converging plates

24. Oceanic - Oceanic Plate Convergence… • Subduction occurs when 2 oceanic plates converge/collide. • The denser plate subducts under the other, a deep ocean trench is formed, and the subducting plate sinks deep into the mantle • This interaction may produce a long chain of volcanic islands known as a Volcanic island arc ( ie. Japan islands)

26. Continental - Continental Plate Convergence… • When continental plates collide, subduction DOES NOT occur because the plates are the same density. • Instead, the plates hit head on and their edges crumple and fold forming great Mountain ranges ( ie. The Himalayas) • The Himalayas are the highest and youngest mountain range and are increasing in height several cm a year due to continuous convergence of the plates!

29. The Himalayas – highest point is Mount Everest and they are found in Asia along the India, Siberia, Tibet, etc…

30. Think you can label the letters with the correct term?

31. 3) Transformation boundaries • 2 plates slide past one another • Because they are sliding horizontally past each other – no mountains or volcanoes are formed • Faultsform (breaks in rock layers due to movement on either side) • San Andreas Fault

32. San Andreas Fault in California

33. Take the Quiz… up to number 7 • Click on the quiz!!

34. Let’s Recap what we know…

35. So… 3 Types of Plate Boundaries DIVERGENT CONVERGENT TRANSFORM

36. When you are really good.. You can understand this whole diagram…