Plate Boundaries

1. Plate Boundaries

2. Plate Tectonic Theory • Both Hess’s discovery and Wegner’s continental drift theory combined into what scientists now call the Plate Tectonic Theory • Theory of Plate Tectonics: • The Earth’s crust and part of the upper mantle are broken into sections, called plates which move on a plastic-like layer of the mantle

5. Effects of Plate Tectonics There are several geological processes that occur where plates meet: 1. Volcanoes- tend to erupt at plate margins as a result of a process called subduction 2. Earthquakes- occur where plates grind against or over one other 3. Mountain building - occurs as one plate is pushed over another 4. Seafloor spreading - occurs where two oceanic plates pull apart

6. Plate Boundaries • The earth’s tectonic plates continue to gradually move even today. The plates interact. Where one plate meets another, it is called a boundary. • Divergent: Boundary between two plates that are moving apart • Convergent: Boundary between two plates that are pushing together. • Subduction Zone: The area where one plate pushes down under another. Volcanoes are often created by this. • Transform (Strike-slip): Boundary between two plates that are sliding past one another.

7. The 3 Types of Plate Boundaries

8. “Convergent, means to come together.” Convergent Boundaries Description: two plates that are pushing together Land Features Formed: island arcs, trenches, volcanoes Actual Examples: Himalayas, Mariana Trench, Hawaiian Islands Picture of Motion: • convergent boundary animation

9. Convergent Boundaries • What can convergent boundaries create? • earthquakes • island formation • mountain forming • volcanoes

10. Types of Convergent Boundaries  Oceanic-Continental • ocean floor plate collides with a less dense continental plate Oceanic-Oceanic  • ocean floor plate collides with another ocean floor plate  Continental-Continental • continental plate collides with another continental plate

11. Convergent Boundaries When two plates collide (converge) one plate moves under the other. This process is called “subduction.”

12. Trench Formation SUBDUCTION When two plates collide (converge) one plate moves under the other Convergent boundary of two oceanic plates. Creates an ________ and a _____. Example: _____ island arc trench Japan

14. Mariana Trench

15. Convergent boundary of an oceanic plate and a continental plate. Forms a _______ mountain range and a ______. Examples: _______ or _______ Mts volcanic trench Cascades Andes

17. Convergent boundary of two continental plates. Forms a ______ mountain range. Examples: ___________, Alps, ______________ folded Himalayas Appalachians

18. The convergent boundary of the Eurasian and Indian Plates has resulted in the formation of the highest mountain range in the world – The Himalayas

19. This illustration shows the movement of the land mass known as India today. As it moved on the Indian plate through time, over millions of years, it finally collided with the Eurasian plate forming the Himalayan Mountains

21. Mount Everest is the tallest mountain in the world, at over 29,000 ft. and is part of the Himalayas. This is a result of the Eurasian and Indian Plates colliding and it is still getting higher as these two plates continue to collide.

22. This map shows the large Himalayan Mountain range that has resulted from the collision of these two continental plates; which continues today.

23. Convergent Boundary – Indian and Eurasian Plates Eurasian Plate Indian Plate

25. “Convergent means to spread apart.” Divergent Boundaries Description: two plates that are diverging, or moving away from each other Land Features Formed: earthquakes, rift valleys, and volcanoes Actual Examples: African rift valley, mid-Atlantic ridge Picture of Motion: • divergent boundary - seafloor

26. Divergent Boundaries • Divergent Boundaries are the boundaries between two plates that are diverging, or moving away from each other. divergent boundary - rift valley

27. When plates are spreading apart from one another there is a lot of geological activity. Earthquakes, and volcanoes occur here. • In some places like East Africa, a rift valley can form that is hundreds of feet deep.

28. Divergent Boundary – Arabian and African Plates Arabian Plate Red Sea African Plate

29. Divergent boundary of two continental plates

30. East African Rift Zone

31. The Mid-Atlantic Ridge is one of the world’s largest divergent plates, running North to South in just about the center of the Atlantic Ocean. All along this ridge, volcanic activity takes place and the sea floor is spreading East and West at a rate of 1.25 cm per year. The divergent plate in Iceland is part of the Mid-Atlantic Ridge.

32. This map shows a divergent plate in Iceland. You can tell from the arrows that the Eurasian Plate and the North American Plate are spreading apart from one another

34. “Transform means slide past one another.” Transform Boundaries Description: two plates that are sliding past one another Land Features Formed: earthquakes Actual Examples: San Andreas Fault Picture of Motion: Transform Boundary

35. Transform Fault Boundaries Transform Boundaries are the boundaries between two plates that are sliding horizontally past one another.

36. Plates Move Side by Side • Transform boundaries neither create nor consume crust. Rather, two plates move against each other, building up tension, then releasing the tension in a sudden and often violent jerk. This sudden jerk creates an earthquake. Earthquakes in Austin

37. Transform-fault boundary where the North American and Pacific plates are moving ____ each other. Example: ________________ in California past San Andreas Fault

38. The San Andreas Fault, seen here, is the result of the Pacific Plate sliding past the North American Plate. This is the site of many of the earthquakes that occur in the United States.

39. Changing Earth’s Surface • Plate movement can alter Earth systems and produce changes in Earth’s surface • Deformation of the crust • Faults • Mountain building • Land subsidence • Volcanoes

40. Mechanism for Plate Tectonics

41. Why do the plates move? • Due to tremendous heat, rock in the asthenosphere is like hot taffy • This allows plates to ride on top of hot, flowing rock • Plates move because heat is being released from deep inside the earth • Convection currents cause hot material to rise and expand (plates diverge) and cooler material to sink and contract (plates converge)

42. Convection Currents Plates are “pushed” and “pulled” over the surface of the Earth due to unbalanced forces. When convection currents reach the surface, plates are pushed apart As the plates move away from each other, part of them are pulled into the Earth’s mantle

43. Because temperature increases with depth, the inside of the earth is very hot. Rock near the core is heated and becomes less dense. It slowly rises while cooler rock nearer the surface is more dense and sinks. This forms convection currents just like those in our atmosphere. Convection Currents As these convection currents in the mantle circulate, they cause the continents above them to move. What Wegener had no way of knowing is that the force that is driving plate tectonics is convection currents in the mantle.

44. Another way to relate to convection currents is like when you boil soup. As the soup heats up, it rises to the top of the container where it begins to cool and sinks, causing convection currents to form, re-creating the same process that takes place in our Earth.

45. As two continental plates move toward each other, what landforms would you expect to see? a. Volcanoes b. Cliffs c. New Land d. Mountains No - These form at edges of plates or over hot spots No - These are erosional landforms or minor uplift areas No - Forms when plates move apart Yes - because 2 continental masses will push into each other and “crumple” the edges to form mountains

46. Where would you find the newest land on Earth? a. In areas of continental convergence b. In areas where two ocean plates come together c. In areas where plates are moving apart d. In areas where two plates are sliding past each other No - Mountains would form here from existing land. No - You would find trenches in this area. Yes - When plates move apart it is due to magma reaching the surface. When magma cools new land is formed. No - You would find land movement but not new land being formed