CHAPTER
18
Plate Tectonics
• Three factors cause the movement of Earth’s tectonic plates:
mantle convection, ridge push, and slab pull.
• Forces at plate boundaries produce landscape features such as
mountains, trenches, and island arches.
CHAPTER
18
Plate Tectonics
• The interactions of
tectonic plates cause
volcanoes and
earthquakes.
• Earthquakes send
waves through Earth.
CHAPTER
18
Plate Tectonics
Activity
• Consider a pot of water sitting on a hotplate. Using your knowledge
of convection (Ch.14), draw a labelled diagram and use arrows to
indicate the rising of warm, less dense water and the falling of cool,
more dense water.
• What would happen if you placed a cork in the
middle of the pot of water? Would it move or
stay in the middle? Why? What force is acting
between the water and the cork causing the cork
to move?
• The cork floating on the water is analogous to
Earth’s crust “floating” on the mantle. Read
page 517 to learn how mantle convection currents
can move tectonic plates.
CHAPTER
18
Plate Tectonics
Key Ideas
• Three factors cause the movement of Earth’s tectonic plates.
• Forces at plate boundaries produce landscape features.
• The interactions of tectonic plates cause volcanoes and earthquakes.
• Earthquakes send waves through Earth.
18.1
Causes and Effects of Plate Movement
• Scientists now believe that three forces work together
to move the tectonic plates:
1. mantle convection
2. ridge push
3. slab pull
VOCABULARY
mantle convection
ridge push
slab pull
18.1
Causes and Effects of Plate Movement
• Uplifted mountains, volcanic belts, and island arcs
are found parallel to convergent boundaries.
• Ocean trenches lie along convergent boundaries.
• Mid-ocean ridges and rift valleys mark divergent
boundaries.
VOCABULARY
mantle convection
ridge push
slab pull
18.2
Geological Events
• Volcanoes are produced over lithosphere cracks and
mantle hot spots.
• Hot spots are rising plumes of hot mantle magma. As
tectonic plates move over the hot spot, a chain of
progressively younger volcanoes is formed opposite
to the direction of plate movement.
• Volcanic island chains and volcanic belts are created
on the overriding plate, parallel to a convergent
boundary.
VOCABULARY
volcano
hot spots
volcanic belt
volcanic island arc
earthquakes
fault
focus
epicentre
shallow-focus
intermediate-focus
deep-focus
seismic wave
body wave
primary wave (P–wave)
secondary wave
(S–wave)
surface wave
18.2
Geological Events
• Earthquakes result when tectonic
forces overcome the friction
between plates. Earthquakes are
categorized based on how far
beneath the surface the focus is
located.
• The sudden movement of the lithosphere during
an earthquake sends seismic waves (vibrations)
through Earth.
• Primary and secondary body
waves travel through Earth,
starting at the focus, the site
of the earthquake within Earth.
• Surface waves travel along
the outside of Earth. They
cause the most destruction.
VOCABULARY
volcano
hot spots
volcanic belt
volcanic island arc
earthquakes
fault
focus
epicentre
shallow-focus
intermediate-focus
deep-focus
seismic wave
body wave
primary wave (P–wave)
secondary wave
(S–wave)
surface wave