Transcript Chapter 5: Earthquakes and Volcanoes

Chapter 5: Earthquakes
and Volcanoes
Section 1 - Earthquakes
What causes earthquakes?
When sudden energy is released from
Earth’s crust breaking or moving which
cause vibrations.
 If the vibrations are large enough they are
felt as earthquakes.

What is a Fault?
A fault is a large fracture in rock along which
movement occurs.
 The type of fault that forms depends on the
forces applied to the rock.

What are the three main
types of faults?
Normal
Fault
Reverse Fault
Strike-Slip Fault
What are Normal Faults?
When rocks are pulled apart under tension
forces.
 Along this fault, rock above the fault moves
DOWN compared to rock below the fault

What are Reverse Faults?

Created when compression forces squeeze rocks
together and rock above a fault moves UP
compared to the rock.
Reverse Fault Animation
What are Strike-slip Faults?
 Shearing
forces
cause rock to
move past each
other in opposite
directions along
Earth’s surface.
Strike Slip Fault Animation
Where do earthquakes
begin?
Inside
the earth at the
FOCUS.

What
a focus?
The focus is the
pointisINSIDE
Earth where
movement first occurs and energy is released.
What is an epicenter?

The epicenter is the point on Earth’s SURFACE
located directly above the focus.
What are Seismic Waves?

Waves of energy that
travel away from the
focus in ALL
directions.
What are the three main types of
seismic waves?
– Primary waves (P-waves)
– Secondary waves (S-waves)
– Surface waves
What are Primary Waves (Pwaves)?
The first waves.
 Travel the fastest through rock material.
 The rock particles move back and forth in
the same direction as the waves are
moving.

Primary Waves Animation
What are Secondary Waves (Swaves)?
 Next waves to occur after Pwaves.
 Jiggle the rock through which
they pass up and down and from
side to side.
Secondary Waves Animation
What are Surface Waves?
Slowest and largest.
 Cause the most destruction.
 Can vibrate side to side, sway or like “waves of
water” across land.

Surface Waves Animation
Summarize your Cornell Notes
notes:
In
AT LEAST five complete
sentences, what did you learn
today?

How are Earthquakes Measured?

By a seismologist who
is a scientist that
studies earthquakes
and seismic waves.

Using a seismograph
which is the
instrument used to
measure seismic
waves.
How do seismologists locate the
epicenter?
They look at the distance between the seismic waves
arrival times.
 Data from at least three different seismograph stations.
 Where the points meet is where the epicenter is located.

What is
magnitude?
 The
measure
of an
earthquake’s
strength.
Earthquake in Japan, 1923
Before
After
How is earthquake strength
(magnitude) measured?
Using the The Richter
Scale which measures
the earthquake’s
magnitude.
 The scale ranges from
1-10;

• 1 = weakest; 10 =
strongest
• As each number goes
up, the strength
increases by 10 and it
releases 32 times
more energy.
How is earthquake damage measured?
By the Modified Mercalli
intensity scale which
measures how much
damage an earthquake
creates.
 The range of intensities
is represented by
Roman numerals.

• The range is from I (1)
to XII (12); I = least
damage, XII = most
damage
Earthquakes with Tim and
Moby!
What are Tsunamis?
Powerful seismic sea waves.
 Occur when an earthquake occurs on the ocean floor.
 Can travel outward from the epicenter in ALL directions.
 When they approach land, the waves slow down and the
height increases.

Tsunamis with
Tim and Moby!
What is seismic safe?
When
a
building will be
able to stand
up against
earthquake
vibrations.
How can we be seismic safe?
 Retrofitting
buildings
 Installing underground pipes that
can bend
 Buildings standing on steel and
rubber supports
 Keep away from all windows;
avoid anything that may fall on
you
Can earthquakes be predicted?
Earthquakes
are unique – no
single change happens to the
Earth before an earthquake
strikes which is why they are
almost impossible to predict.
Summarize your Cornell Notes:
In
AT LEAST five complete
sentences, what did you learn
today?

Chapter 5
Section 2 - Volcanoes
What is a volcano?
A
cone shaped hill or mountain formed
when hot magma, solids and gases erupt
onto Earth’s surface through a vent.
What is magma?
 Molten
rock
material under
the Earth’s
surface.
 Magma can be
pushed upward
by rocks that
surround it.
How do volcanoes form?
Layers of cooled, hardened lava
2. Hot spots
1.
is the
WhatWhat
is lava?
difference
 Molten rock
between
lava
and
materials
above Earth’s magma?
surface.
Magma is INSIDE the
Earth and lava is
OUTSIDE of the Earth.
What is a crater?
 Circular
hole at
the top of a
volcano where
lava and other
volcanic
materials are
released.
What is tephra?
Bits
of rock
or solid lava
that falls
from the air
after an
eruption.
What is subduction?


When two plates collide and the heavier plate
sinks below the lighter plate causing it to
melt which forms a chamber of magma.
Occurs when an oceanic plate collides with a
continental plate or when two oceanic plates
collide.
What is a hot spot?
Weak spots in the crust that allow magma to
rise upward.
 Hot spots are NOT located on plate boundaries.
 The Hawaiian Islands formed because of a hot
spot.

Summarize your Cornell Notes:
In
AT LEAST five complete
sentences, what did you learn
today?

What determines HOW a volcano
will erupt?
Some eruptions are violent and some have just
slow flowing lava quietly down its slopes….
 The “ingredients” of the magma determines
what type of eruption will occur!

– Lava that has more silica (oxygen and silicon) is
thicker and slower.
– Lava that has more iron and magnesium and LESS
silica flows easier and faster.
– Water vapor and other gases can also affect
eruptions.
Types of Volcanoes

There are three major types of volcanoes:
– Shield volcanoes
– Cinder cone volcanoes
– Composite volcanoes or stratovolcanoes
Shield Volcano
Largest type of volcano
 Gentle, hilly slopes


Formed by the build up of basaltic lava layers

Slower lava flows
Shield Volcanoes (cont.)

Forms where magma is forced up from deep in
the Earth OR where plates are diverging
(separating)
– EXAMPLE: Mauna Loa, Hawaii which is the largest
active volcano on Earth.
Cinder Cone Volcanoes
 Relatively
small volcanoes usually less
than 300 meters tall.
 Often form in a group near other larger
volcanoes.
Cinder Cone Volcanoes (cont.)
Formed by medium
force of explosion of
tephra
 Once gas is released
the eruption stops
 Can have short
powerful eruptions or
high eruptions
 EXAMPLE: Sunset
Crater, Arizona

Composite Volcanoes
(Stratovolcanoes)


Steep-sided volcanoes
made of alternating
layers of lava and
tephra.
Sometimes erupting
violently, releasing
large amounts of ash
and gas, which forms a
tephra layer of solid
materials.
Composite Volcanoes (cont.)
Then a “quieter”
eruption forms a lava
layer.
 Forms when one plate
subducts beneath
another.
 Most common type of
volcano
 EXAMPLE: Mount St.
Helens, Washington

Fissure Eruptions
 Fissure
– cracks in Earth’s surface
 Magma that is highly fluid (watery) can
ooze from fissures and form lava
plateaus.
Chapter 5
Section 3 – Earthquakes,
Volcanoes, and Plate
Tectonics
Pacific Ring of Fire
The Pacific Ocean is
almost completely
surrounded by
volcanoes.
 This ring is thousands
of miles long and
contains hundreds of
volcanoes.
 80% of all
earthquakes and
volcanoes happen in
the Ring of Fire.

Ring of Fire
Summarize the notes:
In
AT LEAST five complete
sentences, what did you learn
today?
