1. AKA THE FORCE BEHIND MOUNTAINS, VOLCANOES, AND EARTHQUAKES
PLATE TECTONICS
AKA
THE FORCE BEHIND MOUNTAINS, VOLCANOES, AND EARTHQUAKES

2. The beginning

3. WHO STARTED THIS, ANYWAY?
Back in the day, Sir Francis Bacon (1620) and Benjamin Franklin(1760’s) both remarked on how the “bulge” on the east side of South America seemed to match the “indentation” on the west side of Africa. Other people noted it, also.
FRANK
Ben

4. Alfred Wegener ( a German scientist) first proposed (in 1905) that the continents were drifting around the surface of the earth. His ideas were not generally accepted until the 1950’s, when evidence suggest this idea of “continental drift”.

5. WHAT KIND OF EVIDENCE DID HERR WEGENER HAVE TO SUPPORT HIS THEORY?
SO…….
WHAT KIND OF EVIDENCE DID HERR WEGENER HAVE TO SUPPORT HIS THEORY?

6. Wegener thought that the landmasses fit together like a jigsaw puzzle
Wegener thought that the landmasses fit together like a jigsaw puzzle. He called the land mass “Pangea”.

8. Wegener ‘s investigations revealed that mountain ranges in North America (Appalachians), in Europe (Caledonians), and highlands in England matched or lined up

11. Wegener found matching reptilian fossils on either side of the Atlantic Ocean, that would tend to indicate the continents were once joined.

13. Fossil Evidence

14. Further investigation of glaciation also indicated that the land masses on Earth were once a supercontinent.

17. Continental Drift
Wegener proposed the theory that the crustal plates are moving over the mantle. This was supported by:
fossil evidence
rock type evidence
matching of coastline shapes.
glaciation

18. Wegener was unable to provide any mechanism as to how all this movement took place. It wasn’t until the 1950’s and 1960’s that the Mid-Atlantic ridge was discovered and then things began to really move.
In 1930 Wegener led an expedition to Greenland. He took with some men across the ice, and he never returned. His body was discovered in 1931, marked by skis.

19. The following link provides an insight to Wegener’s ideas and further discoveries about “continental drift”.

20. So----what was the mechanism behind this movement?
In order to understand the mechanism, we need to study the ……….

21. STRUCTURE OF THE EARTH

23. Plate

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

25. Convection Currents
The force responsible for plate movement is __________.

26. SO WE KNOW THAT THE EARTH’S SURFACE HAS CHANGED THROUGHOUT TIME

28. Discovering Plate Boundaries
The following website has an excellent activity for determining the plate boundaries based on several factors. The downloads are free and teacher notes and instructions are included. This activity should take at least 2-3 class periods.

29. Plate boundaries

30. SO…… WHAT EXACTLY HAPPENS AT THESE PLATE BOUNDARIES?

32. Types of Plate Boundaries
1. divergent (constructive)
a. continent from continent
(e.g. mid- Atlantic Ridge)
b. ocean from ocean
(e. g. Red Sea)

33. Red Sea

34. Oceanic Divergent Boundary
Example: Mid-Atlantic Ridge

36. Divergent boundary of two continental plates.
Creates rift valley---East African Rift Valley and Red Sea

37. This image of the Sinai peninsula shows where the Red Sea spreading center forks into two branches which can be seen as forming a brand-new oceanic rift in the land.

38. Continental Divergent Boundary
Example: Red Sea / E. African Rift

39. Continental Divergent Boundary
Example: Baja California

40. 2. Convergent (destructive)
a. ocean-ocean
( e.g.Pacific-Pacific near Marianas Islands)
b. ocean-continent
(e.g. Pacific-North America)
c. continent-continent
(e.g. India-Asia)

42. Oceanic - Oceanic Convergence - Example: Japan
At an ocean-ocean collision, one plate subducts beneath the other, leaving a trace of the process in volcanoes and earthquakes. At the fast collisions (Fiji-Tonga) the subducting plate gets as deep as 700 km while still cool: it is here that you get the deepest (deep focus) earthquakes.

43. Convergent boundary of two oceanic plates.
Aleutian Islands; Japan

45. Convergent boundary of an oceanic plate and a continental plate.
Cascades and Andes

46. Type of fault associated with Convergent Boundaries are called Dip-Slip Faults.

47. Oceanic - Continent Convergence - Example: Andes, Cascades
At an ocean-continent collision, the ocean subducts, and the continent rides high. Volcanoes are built on the continental side due to melt which comes off the subducting plate. Nazca-South America is an excellent example.

48. Convergent boundary of two continental plates.
Appalachians, Himalayas, Alps

50. 3. transform
(e.g. San Andreas fault zone)

52. Transform boundary where the North American and Pacific plates are moving past each other.
San Andreas Fault

53. The type of fault associated with a Transform boundary is called a Strike-Slip Fault.

54. Continental Transform Boundary - Example: San Andreas

55. THE FORMATION OF ONE TYPE OF BOUNDARY OFTEN RESULTS IN THE FORMATION OF ANOTHER.

56. ~800 km
CONVERGENT
DIVERGENT

57. (e. g. Red Sea)

60. Exercise #2 on “plate tectonics.
Now do the exercise on plate tectonics as a review of what you have learned.

62. Plate movements are on the order of a few centimeters/year - about the same rate as your fingernails grow!