1. CHAPTER
Plate Tectonics 18
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.

2. CHAPTER
Plate Tectonics 18
The interactions of tectonic plates cause volcanoes and earthquakes.
Earthquakes send waves through Earth.

3. Plate Tectonics 18 Activity
CHAPTER
Plate Tectonics 18
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.

4. Plate Tectonics 18 Key Ideas
CHAPTER
Plate Tectonics 18
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.

5. Causes and Effects of Plate Movement
18.1
Causes and Effects of Plate Movement
VOCABULARY
mantle convection
ridge push
slab pull
Scientists now believe that three forces work together to move the tectonic plates:
mantle convection
ridge push
slab pull

6. Causes and Effects of Plate Movement
18.1
Causes and Effects of Plate Movement
VOCABULARY
mantle convection
ridge push
slab pull
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.

7. 18.2
Geological Events
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
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.

8. 18.2
Geological Events
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
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.