Chapter 2: What Are Earthquakes and Volcanoes
Transcript of Chapter 2: What Are Earthquakes and Volcanoes
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Earthquakes and Volcanoes
Chapter 2 Lesson 2
Textbook pages 60-69
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*Earthquake
*Epicenter*Fault
*Focus
*Magma
*Seismic waves
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*Most of the time, Earth·splates move very slowly,
and we don·t feel themmove. Other times,Earth·s surface changessuddenly.
*Most major surfacechanges happen nearplate boundaries at whatare called faults.
*Faults are cracks inEarth·s crust where thereis movement.
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*What happens at the
faults?
|Rocks bend and fold
|Rocks lock together andjam
|Over many years, stressbuilds up on the rocks asthe plates push againsteach other until the rocksfinally break.
|The rocks suddenly´snapµ into a newposition, which causesthe Earth·s crust toshake
|There are many differentkinds of faults. (see p. 63)
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� Scientists use a toolcalled a seismograph the
waves of energy that areproduced during anearthquake.are calledseismic waves.
|When scientists talkabout how strong an
earthquake is (itsmagnitude), they use ascale called the Richterscale.
|We may not feel a 3.5
|7.5 is considered amajor earthquake
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|Focus: the point undergroundwhere the rocks are moving
|Epicenter: the point on thesurface directly above thesurface
|Waves that travel throughEarth·s interior (inside Earth)are called body waves
|P waves|S waves (travel slower)
|Waves that travel on thesurface are called L waves
|They are slower and do not goas far from the epicenter
Also see p. 64 in the textbook
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*Most volcanoes start 37 to100 miles below Earth·ssurface where rock becomes
so hot that it melts.*This melted rock is called
magma.
*Melting rock releases gases,which mix with the magma,making it lighter than thesolid rock around it.
*Since it·s lighter, themagma rises. As it rises, itmelts the rock around it,forming a large chamber
below the Earth·s surface.
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*Near the surface, the
magma bursts through an
opening, called a vent.
Once it·s out, it is called
lava. The lava cools and
hardens on the surface.
*This cooled magma builds,
one layer at a time, to
form a volcano.
*Volcanoes also send out
rock fragments and gases
during an eruption.
*Uplifting
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*After an eruption, a volcano usually sinks in at the
top to form a crater.
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� The Pacific Plate is under the
Pacific Ocean.
� Around the edge of the Pacific
Ocean, earthquakes and
volcanoes are caused by thePacific Plate being forced
under other plates.
� What kind of boundaries do
you think these are?
� Converging
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