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Earthquakes and Volcanoes
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Chapter 8 Section 1, pp. 224 - 229
Chapter 9 Section 3, pp. 260 - 265
Standard: The relationship between movement of
the tectonic plates and major geologic events, such
earthquakes and volcanoes
Warm Up:
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Explain the 3 types of faults.
EQ: What causes earthquakes?
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Seismology
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Fault
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Deformation
Elastic Rebound
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Study of earthquakes
Break in the Earth’s crust
along which blocks of crust
slide
Change in shape of a rock
due to stress
Sudden return of a broken,
deformed rock
Energy released as seismic
waves
EQ: What are the 3 kinds of faults?
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Strike-Slip Fault
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Reverse Fault
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Transform motion of
boundary
2 Plates slip past each
other horizontally
Convergent motion of
boundary
Blocks push together,
against each other
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Normal Fault
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NOTE:
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Divergent motion of
boundary
Blocks pull away from
each other
Not all faults are
located at plate
boundaries
Faults can happen along
faults in the middle of a
plate
EQ: How do earthquake waves travel?
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Seismic waves
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P Waves
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A wave of energy that
travels through the
Earth away from an
earthquake in all
directions
A seismic wave that
causes particles of
rock to move in a back
and forth motion.
Waves Continued:
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S Waves
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Body Waves
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Surface Waves
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A seismic wave that
causes particles of
rock to move in a side
to side direction.
Travel through Earth’s
interior
Travel along Earth’s
surface
Ticket out the Door:
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Which wave is most damaging? Explain and
support your answer.
Warm Up:
Are their different types of earthquakes?
Explain.
EQ: How are earthquakes measured?
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Seismograph
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Epicenter
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Focus
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Instrument that records
seismic waves
The point on Earth’s
surface directly above
an earthquake’s
starting point
The starting point
along a fault
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Richter Magnitude
Scale
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Measure the strength
of an earthquake on a
0 – 10 scale
Measure ground
motion or magnitude
(strength)
For each 1 unit of
magnitude , ground
motion increases 10
times
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Intensity of an
Earthquake
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A measure of the
degree to which an
earthquake is felt by
people and the
amount of damage
caused.
Summary
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What do you think is the reason Georgia does not
have many earthquakes?
EQ: What is a Volcano?
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Volcano is a vent of fissure in the Earth’s surface
through which magma and gases are expelled.
Magma is molten rock forced to the Earth’s surface
Lava is magma that flows onto the Earth’s surface
EQ: What are 2 types of
Volcanic Eruptions?
Non-Explosive:
 The most common type of eruption
 Produces relatively calm flows of lava
 Found in much of the seafloor, Northwest regions of
the US, & other vast regions on Earth’s surface
 Examples: Mauna Loa & Kilauea in Hawaii
EQ: What are 2 types of
Volcanic Eruptions continued:
Explosive:
 They are rare, but very destructive
 Clouds of hot debris, ash, and gas repeatedly shoot out
of the volcano
 Pyroclastic flows erupt from the volcano producing
molten rock, which hardens in the air, and dust sized
particles of ash. The ash can reach the upper
atmosphere and circle the Earth for years.
 The lava and large pieces of debris are blasted out of
the volcano in a matter of seconds. This can demolish
an entire mountainside in seconds.
 Example: Mount St. Helens in Washington state
Shield Volcanoes
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Built of layers of lava released from nonexplosive
eruptions.
Lava is very runny
Layers of lava create a volcano with sloping sides
Not very steep sides, but can grow to be enormous
Tallest Mountain on Earth: Mauna Kea in Hawaii
Mauna Loa (in Hawaii)
Cinder Cone Volcanoes
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Made of pyroclastic material from moderate eruptions
Steep sides
Small volcanoes
Erupt for short periods of time
Often occur in clusters on sides of volcanoes
Erode away quickly because pyroclastic material is not
cemented together
Paricutin~Mexican volcano appeared in a cornfield in
1943 and erupted for 9 years
Cerro Negro (in Nicaragua)
Composite Volcanoes
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AKA: Stratovolcanoes
One of the most common types of volcanoes
Form from explosive eruptions of pyroclastic
material followed by quieter lava flows
Lava and pyroclastic material form alternating
layers
Broad bases and steeper towards the top
EX: Mt. Hood, Mt. Shasta, Mt. Ranier, and Mt. St.
Helens (all in US); Mt. Fuji is in Japan
Mount St. Helens (Washington state)
EQ: How does magma form and
move?
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Formation of Magma
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Forms in the lower crust
& upper mantle
Caused by changes in
heat & pressure
Usually the result of
decrease pressure
Rises to the surface since
magma is less dense
than rock
Usually, at plate
boundaries Ex: Ring of
Fire In Pacific Ocean
EQ: Where do volcanoes form?
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@Rift Zones
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Deep cracks between
divergent plates, like
the Mid-Ocean Ridge
in the Pacific & North
Atlantic Oceans
Remember Sea Floor
Spreading
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@Convergent
 At oceanic &
Boundaries/Subduction continental plates
Zones
 Oceanic crust subducts
under continental crust
 Oceanic water mixes
with the mantle rock,
melts it & allows
magma to rise
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@Hot Spots
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Volcanically active
areas far from plate
boundaries
Example: Hawaiian
Islands
EQ: How does a Scientist Predict a
Volcano is going to Erupt?
Classified in 3 categories
 Extinct: has not erupted in recorded history and
probably will never erupt again
 Dormant: currently is not erupting, but the record of
past eruptions suggests the volcano will erupt again
 Active: currently erupting or shows signs of erupting
again in the near future
Summary
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Explain how an earthquake can set off a volcano?