Download Earthquakes and Volcanoes

Earthquakes and Volcanoes
Constructive Forces
Chapter 4 Lesson 2
Pages 178-188
What is an earthquake?
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A sudden movement of
Earth’s crust
The rock on both sides of a
fault is pushed and pulled by
forces in the crust
When layers of rock that are
stuck together suddenly slip,
an earthquake occurs
Slipping along a fault begins
beneath Earth’s surface
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The place where the slipping
begins is called the
earthquake’s focus
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Waves of energy ripple
outward from the focus.
When they reach Earth’s
surface, the waves spread
out from a point directly
above the focus: that point Is
known as the epicenter
The amount of damage an
earthquake causes partly
depends on the amount of
energy released at the
earthquake’s focus
When more energy is
released, more damage is
likely to occur
What is an earthquake?
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Earthquakes happen along
the boundaries of tectonic
plates because the pressure
from the movement of the
plates pushes on nearby
faults
Alaska, Oregon, Washington,
and California are near
tectonic plates and most of
the US Earthquakes occur
here
http://www.youtube.com/watc
h?v=VSgB1IWr6O4
How destructive is an earthquake?
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Earthquakes release more
energy than others.
There are two measure of
earthquakes:The Richter
Scale and the Mercalli Scale
The Richter scale measures
magnitude at the epicenter
– The Mercalli Scale measures
what people felt and what
happened to objects at a
specific location when an
earthquake occurs.
Click Here
http://www.youtube.com/watch?
v=VSgB1IWr6O4Scale
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What are volcanoes?
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An opening in Earth’s crust.
They can form on land and on
the ocean floor
Most volcanoes are found
where tectonic plates meet
and more likely to erupt at
these places
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Eruption is an outpouring of
melted rock, ash, gases, or a
combination of these
Scientists conclude that
volcanoes tend to erupt
where one plate is pushed
under another plate
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Plates melt under great
heat and pressure as
they are pushed down
into the mantle
All volcanoes have at
least one vent or
opening.
Once magma reaches
Earth’s surface it is
called lava.
What are volcanoes?
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An active volcano is currently
erupting or has recently
erupted.
A dormant volcano is one that
has not erupted for some time
An extinct volcano has
stopped erupting or is “dead”
Click for video
http://www.youtube.com/watc
h?v=uZp1dNybgfc
How do volcanoes BUILD land?
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Sometimes magma cools and
hardens before it reaches the
surface
Lava forms solid rock as it
hardens. Over thousands of
years, new lava can increase
the height of a volcano and
form a volcanic mountain=
new land
–
Shield Volcanoes, CinderCone Volcanoes, and
Composite Volcanoes are all
examples of new land
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See page 187 for
pictures
How do volcanoes build islands?
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The Hawaiian Islands are an
island chain, or a line of
volcanic mountains.
As the islands move, they
pass over a stationary pool of
magma called a hot spot.
Over millions of years, lava
erupting from the hot spot
formed a mountain