1. The Earth’s Moving Plates
Earth Science
The Earth’s Moving Plates

2. Plate Boundaries
The movement of the tectonic plates causes both sudden and gradual changes to the Earth’s surface
These changes are related to the three types of plate boundary:
Convergent
Divergent
Transform fault

3. Divergent Boundaries
The spot where two plates are being pulled apart is called a divergent boundaries
The separation of two plates allows magma to rise to the surface and create new crust
Ex. Sea Floor Spreading

4. Divergent Boundaries
The surface of the Earth is changed because the lava can create cones rising up to a kilometer above the ocean floor
This creates the mid-ocean ridges

5. Divergent Boundaries On land divergent boundaries create rift valleys
Iceland is being split by a the diverging of the North American and Eurasian plates
The Saudi Arabian plate and African plate are also diverging

6. Convergent Boundaries
Since new crust is formed at divergent boundaries, and since the Earth isn’t growing, old crust must be getting destroyed
This destruction happens at convergent boundaries

7. Convergent Boundaries
One plate sinks under another plate at the convergent boundary
This sinking is the subduction zone
There are 3 convergent boundaries:
Continental Oceanic
Oceanic oceanic
Continental Continental

8. Continental-Oceanic Convergence
2 land forms are created at the boundaries:
Mountains
Ocean trenches
Mountains = the crust raised up much higher that that surrounding it
Trenches are steep depressions along the edge of continents

9. Oceanic-Oceanic Convergence
One oceanic plate will be subducted under the other
This forms trenches
Challenger Deep formed at the Pacific and Philippine plate boundary (11000m) is the deepest trench
Volcanic activity also gives rise to volcanic islands

10. Continent-Continent Convergence
There is no subduction zone when continents converge
2 land forms are created:
Mountains
Plateaus
Plateaus are areas of high level ground

11. Transform Fault Boundaries
Discovered by a Canadian Scientist, J Tuzo Wilson , while using paper to model faults
They are areas where convergent or divergent boundaries transform (change) into a fault

12. Transform Fault Boundaries
A fault is an area where rock is being broken by plate movement
Plates slide along each other in opposite directions at transform fault boundaries

13. Transform Fault Boundaries
These boundaries are mostly in the ocean
The San Andreas fault is a famous terrestrial fault
W. California on the Pacific Plate moves north past E. California on the N. A. plate
These boundaries cause many shallow earthquakes

14. Review of Plate Boundaries
There are 3 kinds of plate boundaries:
Convergent
Divergent
Transform Fault
Plate boundaries change the Earth’s crust
Ocean trenches and rift valleys
Mountain building
Plateaus
The plate boundaries also create earthquakes and volcanoes

16. Earthquakes How Earthquakes Happen
Earth Science
Earthquakes
How Earthquakes Happen

17. Effects of Plate Movement
Earthquakes result from plate movement
Because plates are not smooth they lock together
Pressure builds up at the lock until the plates suddenly move
The energy released by the movement causes vibrations that move through the crust
Earthquake animation

18. Earthquakes The vibrations are called earthquakes
Earthquakes occur at convergent, divergent, and transform fault boundaries
IRIS Seismic Monitor
Canadian Earthquakes

19. Divergent Boundary Earthquakes
The quakes occur when the pressure of magma pushing upward is great enough to split the crust above it
These quakes are small, local and constant along the Atlantic mid ocean ridge

20. Convergent Boundary Earthquakes
At subduction zones, the bottom plate gets stuck on the top plate
When the stuck spot breaks free the top plate moves causing a large earthquake
The longer the stick, the greater the quake

21. Convergent Quakes in BC
Southern BC has ~200 quakes a year as the North American plate subducts the Juan de Fuca plate

22. Transform Fault Boundary Earthquakes
Plates moving past each other in opposite directions can also get stuck
Like a convergent earthquake the longer it takes before the plates unstick the stronger the quake

23. Transform Fault Boundary Earthquakes
Many strong quakes occur along the San Andrea-North American fault

24. Effects of Earthquakes
Earthquakes can cause dramatic damage
The damage occurs due to seismic waves
Earthquakes often happen deep in the crust
The spot the earthquake occurs is the focus
Residential damage in Prince William Sound, Alaska, due to liquefaction caused by a magnitude earthquake.

25. Effects of Earthquakes
The spot on land over the earthquake is the epicenter
Seismic waves are shock waves that move off in all directions from the focus

26. Effects of Earthquakes
There are 2 main types of seismic waves:
P waves- primary waves (compress)
S waves- secondary waves (sheer)

27. Seismic Waves Both S waves P waves Originate from the same focus
Travels through liquids and solids
Push and pull material as they move
Travel ~8 km/s
Cause the first movement felt in a quake
Both
Originate from the same focus
Begin at the same time
Can be felt at the Earth’s surface
S waves
Travel through solids only
Make the rocks vibrate up, down, or sideways
Travel ~4.5km/s
Usually cause more building damage

28. Damage from Earthquakes
Earthquakes damage human structures:
Buildings
Roads
Tunnels and overpasses
Water lines
Fuel lines and tanks
Fires, lack of water and being crushed all endanger people

29. Tsunamis Tsunamis are another danger of earthquakes
Tsunamis are series of ocean waves created by the quake
The are small in the open ocean but travel at up to 800 km/h
They slow as they approach shore, but rise to heights of up to 30m

30. - often form from the friction between moving tectonic plates.
Earthquakes
- often form from the friction between moving tectonic plates.
This accounts for 95 %
of all earthquakes.
The Juan de Fuca convergent
plate boundary west of
Vancouver Island has many
earthquakes.
Large earthquakes hit this
region every years.
Transform boundary
San Andreas fault

31. Describing Earthquakes
Scientists understand why they happen, but it is very difficult to predict their timing, exact location, and strength.
Their pressure build-up happens underground, over very long periods of time.
The focus of the earthquake is where the pressure is finally released.
The epicentre is the point on the surface directly above the focus.

32. Release of energy starts here...

33. Earthquakes occur at various depths, depending on the plates involved.
Depth of Earthquakes
Earthquakes occur at various depths, depending on the plates involved.
Earthquakes at the surface tend to cause more damage.
See page 528

34. Earthquake Magnitude Scale
Earthquake Effects
Estimated Number Each Year
2.5 or less
Usually not felt, but can be recorded by seismograph.
900,000
2.5 to 5.4
Often felt, but only causes minor damage.
30,000
5.5 to 6.0
Slight damage to buildings and other structures.
500
6.1 to 6.9
May cause a lot of damage in very populated areas.
100
7.0 to 7.9
Major earthquake. Serious damage. 20
8.0 or greater
Great earthquake. Can totally destroy communities near the epicenter.
One every 5 to 10 years

35. Earthquake Waves Earthquakes produce seismic waves.
Seismology is the study of these waves.
These waves reveal the source and strength of an earthquake.
They also help us learn about the composition and distances of the Earth’s interior.

36. Earthquake Waves
Types of earthquake waves:
See page 529

37. Seismic Waves
Seismic waves behave differently in different Earth layers.
Knowing this, scientists can learn about earthquakes and Earth’s interior.
Seismometers are used to measure seismic wave energy.
Early seismometers just measured whether the ground shook.
Some seismometers measure horizontal movement, others vertical movement.

38. Seismograms
A seismogram is produced, showing when an earthquake started, how long it lasted, and the magnitude.
1 increase in magnitude
= 10X stronger
A magnitude 6 earthquake
is 100X more powerful
than a 4.
Since seismic waves travel
at different speeds, a
distance-time graph can reveal the focus.

39. Review of Earthquakes
Earthquakes occur at all 3 types of plate boundaries
Earthquakes result from the release of pressure built up due to plates sticking together
The energy released creates two types of seismic waves: P and S
Earthquakes cause massive damage

40. Earth Science 7
Volcanoes

41. Volcanoes One of the effects of moving plates are volcanoes
Volcanoes are openings in the earth’s crust that allow magma and other materials to come through

42. Plates and Volcanoes
The location of a volcano affects the behavior and composition of the volcano
Three locations volcanoes occur are:
At divergent boundaries
At convergent boundaries
At hot spots

43. Volcanoes at Divergent Boundaries
Magma pushes plates apart and moves to the surface here
75% of lava is produced at these boundaries
Lava hardens quickly in the water and builds undersea mountains and islands

44. Volcanoes at Divergent Boundaries
The youngest volcanoes in BC are on Mt. Edna, Hoodoo Mount, Lava Fork, and Crow Lagoon
Stikine Volcanic Belt
They are on a divergent boundary in the North West corner of BC near Alaska
It has been 150 years since any of them erupted

45. Volcanoes at Convergent Boundaries
The magma at convergent boundaries is thicker than at divergent boundaries
Gases cannot escape until tremendous pressure builds up causing explosive release
Gases, lava and ash are all blasted out of the volcanoes by the force

46. Volcanoes at Convergent Boundaries
The last explosive eruption in BC occurred at Mt. Meager near Whistler 2350 years ago
(long, long ago)

47. Hot Spot Volcanoes
These volcanoes are the exceptions to activity along plate boundaries
Hot spots are areas where the mantle temperature is higher than normal

48. Hot Spot Volcanoes Large pools of magma collect at hot spots
The magma melts the overlying rock and lava pours out
The lava is runny so gases escape easily and eruptions are rarely explosive

49. Hot Spot Volcanoes
When these volcanoes are in the ocean the lava quickly hardens into a steep cone
The cone may rise to form an island; This is the way the Hawaiian islands formed

50. Hot Spot Volcanoes There is a hot spot in British Columbia!
The Anahim Volcanic Belt stretches from Quesnel to the west coast
/volcanoes/map/inde x_e.php

51. Volcano Composition
Volcanoes can also be classified by their composition
Cinder cone volcanoes- smallest of the three volcanoes
Cone has steep sides
Bowl shaped cone at the top
Built from layers of ash and volcanic rock
They erupt violently

52. Volcano Composition
Shield volcanoes are the largest of the 3 types of volcanoes
They are made of cooled lava
The cones have gently sloping sides
These form at hot spots and divergent boundaries
They erupt quietly

53. Volcano Composition
Composite(strato) volcanoes are a mix of the other two volcanoes
They are made of alternating layers of lava and ash
They may erupt violently or quietly

54. Volcanoes The movement of tectonic plates causes volcano formation.
Composite volcanoes – found along plate boundaries
Layers of ash and thick
lava form a tall cone.
As magma reaches the
surface, it cools, hardens,
and traps gases below.
Pressure builds;
eventually, there is
an eruption.
See pages
Mount St. Helens is a composite volcano.

55. Mt St Helen’s, Washington

56. 2. Shield Volcanoes 3. Rift Eruptions
– these are not found at plate boundaries but instead form over hot spots.
Thin magma/lava flows out from a hot spot
and forms a low, wide cone.
The Hawaiian Islands are an example of a chain of shield volcanoes
3. Rift Eruptions
– occur along long cracks in the lithosphere
These are not explosive, but they release massive amounts of lava.

57. Shaped like a “soldier’s shield” lying down

58. Occur when magma erupts through long cracks in lithosphere
Occur when magma erupts through long cracks in lithosphere. Curtain-like fountains of lava erupt at spreading ocean ridges or rifts in continental crust. Can release enormous amounts of lava.
Take the Section 12.2 Quiz

59. The Effects of Volcanoes
Volcanoes effect the environment
Some effects are destructive, and some are beneficial

60. The Destructive Effects of Volcanoes
Volcanic ash in the atmosphere clouds the amount and reduces Earth’s temperature
Buries the surrounding area in 10s of meters of mud and ash
flows of mud, and lava can destroy stationary objects in their path
Pyroclastic flows (hot clouds) cook and suffocate living things

61. The Beneficial Effects of Volcanoes
The beneficial effects of volcanoes are:
Ash improves soil
Diamonds form in volcanic rock
Obsidian is formed from lava
Obsidian is used for scalpels in eye surgery today, and was important in aboriginal tool making.

62. Review of Volcanoes Volcanoes change the Earth’s crust
Volcanoes form at different locations
Divergent boundaries
Convergent boundaries
Hot spots
Volcanoes have destructive and beneficial effects