Download UNIT ONE A Changing Earth

Earthquakes and
Volcanoes
EARTHQUAKES
Plate Tectonics
• Lithosphere – the crust and upper part of the
earth’s mantle
1. Inner Core
4
3
1
2. Outer Core
3. Mantle
2
4. Crust
EARTHQUAKES
Plate Tectonics
• Plates – large pieces of the lithosphere
• Theory of plate tectonics – the idea that the
earth’s crust is made of moving plates
• Plate Boundaries – places where the plates meet
– Scientists think as the magma in the Earth’s mantle
moves, it causes the plate boundaries to collide,
separate or slide along each other.
EARTHQUAKES
Plate Tectonics
• Scientists believe the Earth is made up of large
plates that float on the partly melted rock of the
Earth’s mantle.
• Pangaea – a large landmass that some scientists
think may have existed at one time
– No recorded observations
EARTHQUAKES
Causes of Earthquakes
• Earthquakes often occur when rocks along the
plate boundaries shift suddenly and release
stored energy.
• Construction of large buildings and the movement
of molten rock under a volcano can also cause
earthquakes.
EARTHQUAKES
Causes of Earthquakes
• Faults – breaks in the earth’s surface along which
rocks can move
– Three kinds of faults – determined by how the rocks
move against each other (thrust or reverse fault, normal
fault, strike-slip fault)
• Reverse fault – rocks push together until a section of
rock moves upward
EARTHQUAKES
Causes of Earthquakes
– Three kinds of faults – determined by how the rocks
move against each other (thrust or reverse fault, normal
fault, strike-slip fault)
• Normal fault – rocks moving apart
• Strike-slip fault – rocks moving horizontally past
each other
EARTHQUAKES
Earthquake Waves
• Earthquake is vibration or shaking of the earth’s
crust.
• What causes earthquakes: Plates move pass
each other, pressure builds up enough that rock
break, and the plates move suddenly.
• Focus (A) – beginning point of an earthquake
• Seismic waves – vibrations that flow out from the
beginning point of an earthquake
• Epicenter (B) – the point on the surface of the
earth directly above the focus
A= Focus
B= Epicenter
EARTHQUAKES
Earthquake Waves
• Body waves – seismic waves that occur beneath
the surface of the earth
– P Waves – primary waves; fastest moving; travel in a
straight path by a push and pull motion; these waves
move back and forth
S Waves – secondary waves;
move more slowly; move in an
up and down zigzag pattern;
causes the particles in the rock
to vibrate to the direction in
EARTHQUAKES
Earthquake Waves
• Surface Waves: the slowest moving and most
destructive waves
– Can move back and forth in a zig zag pattern; fastest
moving land waves
– Can move in a circular pattern; rolling motion along the
ground
EARTHQUAKES
Detecting Earthquakes
• Seismograph – a machine that detects, times,
and measures the movement of the earth
• Seismograms – records of the movements of the
earth
• Seismologists – scientists who study the
movement of the earth
EARTHQUAKES
Measuring Earthquakes
• Mercalli scale – based on the amount of
destruction caused to man-made structures
– Measures observable destruction
• Richter scale – measures the magnitude of an
earthquake’s seismic waves and assigns it a
number
– Magnitude – strength of the seismic waves of an
earthquake, this is how much energy is released.
EARTHQUAKES
Building for Earthquakes
• Features that help structures withstand
earthquakes:
– Concrete reinforced with steel rods
– Foundation laid in rock
– Steel framing
EARTHQUAKES
Related Disasters
• Tsunami – giant ocean waves triggered by
earthquakes, volcanoes, or landslides
• Other catastrophic events associated with
earthquakes:
– Volcanic eruptions
– Landslides
VOLCANOES
• Magma – molten rock under the earth
• Volcano – are a form of a mountain, they occur
when a crack in the earth’s surface allows
magma and gases to come to the surface
• Volcanologists – scientists who study volcanoes
• Magma chambers – pockets of molten rock in the
earth’s lithosphere
• Lava – hot molten rock that breaks through the
surface of the earth
• Vent – opening in the surface of the earth through
which lava flows
• Crater – the bowl shape at the top of a main vent
VOLCANOES
Causes of Volcanoes
• Volcanic ash – jagged bits of crushed rock
• Volcanic cone – funnel-shaped mound
Draw this Diagram in
your notes.
1
2
1. Side Vent
3
4
2. Vent
3. Lava
4. Magma Chamber
5
VOLCANOES
Locations of Volcanoes
• Volcanic activity may occur under the ocean, at
hot spots, along plate boundaries, and along the
Ring of Fire.
• Ring of Fire – active volcanoes around the edges
of the Pacific Ocean
• Under water eruptions (submarine eruptions) are
20x more frequent than eruptions on land
• Hot spots – places where a pool of very hot
magma rises toward the surface and forms new
land
VOLCANOES – Classifying
By Shape
• Shield volcano – large, gradually sloping sides;
erupts continuous flowing lava; mild, continuous
eruptions
• Cinder cone – resembles a hill; has a bowl-like
crater; usually has more than one vent; made of
cinders
– Cinders – bits of ash and lava
• Composite cone – steep sides and layers of lava
and tephra
– Tephra – a mixture of cinders, ash, and rock emitted by
a volcano
VOLCANOES – Classifying
By How Often They Erupt
• Volcanoes can have more than one kind of
eruption because one eruption can change the
conditions inside a volcano, causing it to erupt
differently the next time.
• Active volcano – one that has erupted at some
point during a recorded time period and is
expected to erupt again
• Dormant volcano – has erupted in the distant past
but is currently inactive and not expected to erupt
again
• Extinct volcano – does not have a recorded
eruption and is not expected to erupt in the future
– There is NO guarantee that it will remain extinct
VOLCANOES – Classifying
By The Type of Eruption
• Hawaiian eruption – runny lava and little or no cinder,
ash or steam; quiet; may continue for long periods of
time
• Strombolian eruption – fountain of lava that runs down
the sides
• Vulcanian eruption – violent; causes a loud explosion
that sends lava, ash, cinders, and gas into the air
• Pelean eruption – produces a pyroclastic flow
(avalanche of red-hot dust and gases emitted by a
volcano)
• Plinian eruption – most powerful; spews lava, blows
gases, ash, and debris into the atmosphere
• Pyroclastic flow – a high-speed flow of very hot gases
and dust
VOLCANOES
Effects of Volcanoes
• Vog – volcanic gases; volcanic fog; pollutes the
air and can cause acid rain and respiratory
problems
• The gases, ash, and dust of volcanoes can cause
cooling in the weather.
• Dangers of Volcanoes
– Debris flow – when part of the mountain collapses and
mud and rock fragments surge down the mountain
• Products of Volcanoes
– Soil rich in nutrients, valuable gems
– Igneous rock – formed as magma and lava cool and
harden
VOLCANOES
Effects of Volcanoes
• Other thermal eruptions
– Hot spring – a heated pool of warmed ground water
• Geyser – a hot spring that blows steam and water
into the air
• Mud pots – a hot spring that contains more mud than
water
Review for CFA #11 Earthquakes & Volcanoes
1.
Earthquakes occur along breaks in the earth surface, these breaks are
called___________. List and Describe the 3 types.
2. The _________is the beginning part of an earthquake & the ____________is the point
on the surface of the earth directly above the focus.
3. ________ ________ are the vibrations that flow out of the beginning point of an
earthquake. List and Describe the 3 types.
4. What are the 2 scales used to measure the strength of an earthquake? How do they
differ?
5. What is magnitude?
6. What is a volcano?
7. Where can volcanic activity occur?
8. What is the ring of fire?
9. What are some of the effects of a volcanic eruption?
10. What types of geological events occur at plate boundaries?