Transcript Earthquakes and Volcanoes

Earthquakes and Volcanoes
p. 346 - 353
What is This?
Why do Earthquakes Occur?
• Stress builds up at a fault
• Stress is a force that adds potential energy to
the rock
• As soon as the rock slips, energy is released
Why do Earthquakes Occur?
• When there is sudden movement along a fault
• The fault suddenly breaks and slides
Focus and Epicenter
• The focus of an earthquake is the area
underground where rock moves. The focus is
where waves are sent out
• The epicenter of an earthquake is the location
on the earth’s surface directly above the focus
Focus and Epicenter
Waves are Released
seismic waves
P and S waves
• P: Primary Wave – causes the initial jolt of the earthquake.
Compresses the rock as it travels
• S: Secondary Wave – slower and stronger wave. Shakes the
ground in many directions
Volcanoes
• A volcano is a weak spot in the crust where
magma comes to the surface.
• Magma that reaches earth’s surface is called
lava.
magma
lava
Lava
- Lava cools to form solid rock
- Volcanic activity builds mountains!
Volcanoes at Convergent Boundaries
Island Arcs
• String of islands at an oceanic – oceanic
convergent boundary
• Japan, New Zealand, Indonesia, Caribbean
islands
Volcanoes at Divergent Boundaries
Hot Spot Volcanoes
• Hawaii was formed this way
• Hot area under the surface –
plate moves on top. As the
plate moves, a chain of
volcanoes is formed.
• Watch the animation:
http://esminfo.prenhall.com/
science/geoanimations/anima
tions/35_VolcanicAct.html
What is a Tsunami?
Earthquake or volcanic activity under the
ocean can lead to strong waves, creating
a tsunami.