The document discusses how plate tectonics and the movement of tectonic plates creates different landforms on Earth. It explains that plates can move together, apart, or side by side, and each type of movement results in distinct landforms. Plates colliding form mountains like the Himalayas. Plates pulling apart form underwater mountain ranges like the Mid-Atlantic Ridge. Plates sliding past each other cause earthquakes along faults like the San Andreas Fault. Some volcanoes form from hotspots in plate interiors, like the Hawaiian Islands.

1. How Plate
Movements
Create
Landforms
By Moira Whitehouse PhD

2. Understanding how the plates of the
Earth move help us understand how
some landforms on Earth are built.
The forces of plate movements are
constructive forces—forces that build
new landforms on the surface of the
Earth.

3. Remember how
the crust of the
Earth is broken
into huge pieces
of rock called
plates. These
plates fit together
around the globe
like a giant jigsaw
puzzle.

4. The plates move as
they float on the
hot, melted rock
found in the mantle.
Creative Commons
Wikipedia Commons

5. The Earth’s crust consists of the oceanic and
the continental crusts, both of which float on
the magma (melted rock).
• The oceanic crust is the layer of
rock which forms the floor of an
ocean. It is about 4-7 miles thick.
• The continental crust is the layer of rock
which forms the continents and those areas
magma
of shallow seabed close to the shore. The
continental crust is much thicker than the
oceanic crust--about 19 miles thick.

6. The continental crust is mainly made of a
rock called granite.
The oceanic crust is made of mostly
basalt, a very dense rock that is much
heavier than the granite of the continental
crust.
As a result, the oceanic crust sinks deeper
into the magma (the molten rock) when
the continental and oceanic crust meet.

7. This rock
is mainly
granite.
This rock
magma is mainly
basalt.

8. Wikipedia commons
First of all, notice that most plates have both
Wikipedia Commons
oceanic and continental crust and that few
have only oceanic crust.

9. Wikipedia Commons
Wikipedia commons
Notice the arrows to see how the plates interact.

10. You may have noticed that plates can move
in one of three ways:
1. together
2. apart
3. side by side

11. This map of volcano and earthquake activity
mirrors a map of plate boundaries.
Image for educational use http//serc.carleton.educ

12. Two continental
plates colliding

13. USGS
When two continental plates collide, the rock
where the two plates meet rises and folds
forming jagged mountains.

14. These collisions produce Earth’s most
spectacular mountain ranges and deepest
valleys.
Mountain ranges that were formed in this
way include the Himalayas where the
Indian Plate is moving into the Eurasian
Plate.
The Himalayas are the highest mountains in
the world, towering as high as 29,000 feet.

15. Wikipedia commons

16. Wikipedia Commons
Himalayan Mountains from the air

17. Pictures of folded mountains.
The
Himalayas, the
Andes in South
America, the
Alps, the Rocky
Mountains and
the Appalachian
Mountains are all
folded mountains.
Pics4learning

18. When continental plates meet and push
up “new” mountains, the land behind the
mountain chain often is also up lifted.
However, it doesn’t break or fold. As a
result a high flat area is formed---a
plateau.
The Tibetan Plateau was created when the
Indian Plate and Eurasian Plate collided.
The Himalayan Mountains formed along
the edge of the collision, and the unbroken
plateau behind them rose as a “flat table”.

19. USGS

20. Continental and
oceanic plates
colliding

21. When an oceanic plate moves into a
continental plate, it slides under
because it is denser and thus, heavier.
The extreme heat and
pressure causes the
leading edge
of the oceanic
plate to melt. USGS
The resulting magma rises and gathers in
pools under the continental crust.

22. As a result:
First, a deep ocean trench forms where the
oceanic plate moves under the continental
plate.
Second, when enough magma collects in the
pools under the continental plate, and
enough pressure develops, a volcano erupts.

23. Image courtesy of FEMA
USGS

24. An example of an oceanic plate is moving
under a continental plate would be on the
western coast of South America.
•The Nasca Plate (oceanic plate) is moving
under the South American Plate.
Result: the Andes Mountains.
Many volcanoes and
earthquakes occur in this region.

25. Wikipedia commons

26. Image courtesy of National Geographic
Andes Mountains

27. Another place, closer to home, where an
oceanic plate is moving under a
continental plate is on the west coast of
United States.
There a small oceanic plate called the Juan
de Fuca Plate is subducting (moving under)
under the North American Plate.

28. This subduction is
occurring on the
coast of Washington
state, Oregon and
northern California.
The Juan de Fuca
Plate, what is left of
an old oceanic
plate, is pushing
under the North
American Plate.

29. This subduction
results in the
building of the
Cascade Mountain
Range. Well-
known volcanoes
in this range are
Mount St.
Helens, Mount
Adams and Mount
Hood.

30. Wikipedia commons
Mount St. Helens erupting in 1980

31. Now we will consider where two plates
pull apart.
We will look at what happens when two
oceanic plates move apart.

32. Oceanic plates
moving apart

33. When two oceanic
plates move
apart, magma from the
mantle flows upward
filling the gap between
the two plates. When
the lava hits the cold
water it solidifies as
basalt rock. Image courtesy of USGS
If this process occurs over a long, long time, a
new mountain range is built. This type of
mountain chain is called a midoceanic ridge.

34. Wikipedia commons

35. Wikipedia Commons
Here we see magma building up to form a
chain of mountains as two oceanic plates pull
apart.
As a result of this process, new oceanic crust is
continuously being built.

36. This is what is happening
in the middle of the
Atlantic Ocean. The North
American plate and the
Eurasian plates are pulling
apart in the North Atlantic
and the South American
plate and the African plate
in the South Atlantic.
usgs

37. Magma oozing out
of these “pull
aparts” over
millions and millions
of years has built
and is still building
an underwater
mountain range
down the middle of
the Atlantic Ocean
called the Mid- http://www.navmetoccom.
Atlantic Ridge.

38. Iceland is an
example of an
island formed
by magma that
came from
between
diverging
oceanic plates.
It sits on top of
the Mid-
Atlantic Ridge.
USGS

39. Photos from Iceland
http://www.flickr.com
javier.losa'sphotostream

40. Image from NASA
Here we see a chain of mountains being built
under all Earth’s oceans where ocean plates move apart.

41. As the ocean plates move apart, the oceans
are getting wider--a few centimeters each
year.
As a result, oceans all over the world are
increasing in size. However, at the same
time, new continents are building at the
faults (cracks) that run down the middle
of these oceans.

42. Tectonic plates
that move side
by side

43. Now we will consider where two plates
slide side by side:
This type of movement commonly
produces earthquakes.

44. Sometime the touching surfaces get stuck.
As the movement of the plates
continues, pressure builds up.
When pressure to move is greater than the
force holding the surfaces still, a sudden
violent thrust occurs.
This is an earthquake.
Earthquakes are common where plates slide by
one another.

45. We have our own transform fault. Along the
west coast of North American, the Pacific
Plate is sliding past the North America Plate
creating a fault called the San Andreas Fault.
In fact, the Pacific Plate is very gradually
carrying the western-most part of
California northward.
The city of Los Angeles rides on top of
the oceanic Pacific plate.

46. Let’s look at that image of the plates again.
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47. Here you can
see the Pacific
Plate moving
northeast and
the
NorthAmerican
Plate sliding
southwest
creating the San
Andreas Fault.

48. In some parts of
California, you can actually
see the San Andreas Fault
line where the two plates
are sliding by one another.
The land to the west of the
San Andreas Fault is slowly
moving north. The land to
the east of the fault is
moving south.
Aerial view of the fault USGS

49. 1906 San Francisco
earthquake
Wikipedia commons
1994 collapse of Los
Angeles overpass
http://wapedia.mobi/en/Northridge_earthquake

50. “Hot spot”
volcanic activity

51. Most earthquakes and volcanic eruptions
occur where plates move together, apart
or side by side.
However, a few volcanoes erupt in the
middle of plates.

52. Red dots are some of the hotspots
found around the world.
usgs
For example, the Hawaiian Islands, which are
entirely of volcanic origin, have formed in the
middle of the Pacific Ocean more than 3,200
km from the nearest plate boundary.

53. How do the
Hawaiian Islands
and other
volcanoes that
form in the
interior of plates
fit into the plate
tectonics
picture?
http://www.flickr.com/ mccum934

54. Scientists believe that below the crust in
these areas, a hot plume of magma rises
from deep within the Earth. When the plumes
breaking through the Earth’s surface a volcano
erupts. These plumes are thought to be
stationary relative to the plates that move
over them. So as the plate
moves on the present volcano becomes
extinct and a new one develops above the
plume forming new land.

55. Source: Maurice Krafft, Centre de
Volcanologie, France)

56. Image courtesy of National Geographic
Mount Kilauea in Hawaii erupting

57. Now let us review.
Look at each landform shown.
Be ready to show by moving your hands
and by telling us how each landform was
formed.

58. Wikipedia Commons
Himalayan Mountains from the air

59. Wikipedia commons
Mount St. Helens erupting in 1980

60. Image courtesy of National Geographic
Mount Kīlauea volcano erupting in Hawaii.

61. http://www.arthursclipart.org/
Earthquake

62. Image from NASA
A chain of mountains being built under all Earth’s oceans.