Earthquakes

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Earthquakes
Volcanoes
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(No Transcript)
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I. Earthquakes
A. Earthquakes - The shaking and trembling that
result from sudden movements of the Earths crust.
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B. Occurences
1. Over one million earthquakes occur every year.
2. Most are so small that Earths surface barely
moves.
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3. Several thousand actually move the surface

4. Several hundred cause noticeable changes in
the Earths surface.
5. About 20 cause severe changes in the Earths
surface.
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C. The most common cause of earthquakes is
faulting.
1. Fault - A crack in the earths crust along
which rocks move.
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2. Faulting - The process of the Earths crust
moving along a fault, the cause of most
earthquakes.
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D. Earthquakes that occur on the ocean floor can
cause giant sea waves called Tsunamis.
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1. Travel at speeds of 700 - 800 km/hr.
2. Can reach heights of over 20 meters (6- story
building)
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E. Focus - The point beneath the Earth where
rocks break and move.
F. Epicenter - The surface point directly above
the focus of an earthquake, where the most
violent shaking occurs.
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G. Seismic Waves
1. Seismograph - Instrument that detects and
measures seismic waves, it prints wavy line on
paper.
2. Seismogram - The record of waves produced by
seismograph.
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3. Seismologist - Scientists that study
earthquakes.
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4. Richter Scale - Scale used to measure the
relative strength of an earthquake, (scale
ranges 1-10, over 6 is destructive)
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II. Volcanoes
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A. Magma - Hot liquid rock that exists beneath
the earths surface, magma exists in pockets
called magma chamber.
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B. Lava
Magma that has reached the Earths surface.
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C. Volcano - The place in the Earths surface
where magma becomes Lava, the actual hole the
magma exits through.
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D. Vent - The opening from which lava erupts.
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E. Volcanic Eruptions
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1. Volcanic Dust - The smallest rock particles
from an eruption, less than .25mm (like flour)
2. Volcanic Ash - Particles more than .25mm
(like grains of rice)
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3. Volcanic Bombs - Large rock particles from a
few centimeters to several meters across (from
golf balls to boulders)
4. Cinders - Golf ball size volcanic bombs
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F. Types of Volcanoes
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1. Cinder Cone Volcano - Made of cinders and
other rock particles that have been blown into
the air.
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2. Shield Volcano - Composed of quiet lava flows
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3. Composite Volcano - Built up of alternating
layers of rock particles and lava.
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G. Crater - Funnel-shaped pit or depression on
top of a volcanic cone.
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H. Caldera - Crater that has become very large
from the collapse of its walls.
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I. Most major earthquakes and volcanic
eruptions occur in three zones around the world,
the Earths crust is very active in these zones.
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The End