EARTHQUAKES, VOLCANOES,
TSUNAMIS
Integrated Science
Volcano
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A mountain that forms when magma reaches the
surface.
Under certain conditions, small amounts of mantle
rock can melt, forming liquid magma. The magma
rises upward through the crust, erupting at the
surface as a volcano.
Magma rises because it is less dense than the solid
rock around and above it.
Structure of a Volcano
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Before an eruption magma often collects in a
pocket called a magma chamber.
Magma rises to the surface in a narrow, vertical
channel – pipe.
Vent- opening in ground where magma escapes to
surface.
Crater- top of the central vent in most volcanoes is a
bowl-shaped pit.
Caldera- chamber and main vent when empty may
fall in creating a huge depression.
Location of Volcanoes
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Most occur along plate boundaries or at hot spots in
the crust.
Hot Spot- region where hot rock extends from deep
within the mantle to the surface.
3 major types of Volcanoes
Shield volcanoes- quiet eruption of low-viscosity lava
and produces a wide, flat volcano.
 Cinder
cones- Eruption that is entirely ash and cinders
and results in a small, steep-sided volcano.
 Composite
volcanoes- Explosive eruptions that
produce a combination of lava and ash.
How a Volcano Erupts
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Magma is under pressure and contains dissolved
gases (Carbon dioxide and water vapor).
As magma approaches the surface, lower pressure
allows the gases in magma to expand rapidly.
Eruption occurs when the gases bubble out through
a crack in the crust.
Quiet and Explosive Eruptions
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Quiet- very hot, low-silica magma generally erupt
quietly.
 Lava
erupts in a stream of low-viscosity lava called a
lava flow.
Explosive- high-silica magma. Thick magma can clog a
volcanic pipe causing enormous pressure to build up.
Trapped steam inside the volcano adds to the pressure.
- Lava solidifies quickly
Significant Eruptions and Environmental
Impacts
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Mount St. Helens (1980)- Washington State, killed 57
people and large numbers of wild animals. Large areas
of forests were obliterated. Through succession some
vegetation has returned.
A positive from volcanoes is highly fertile soils from
weathering of lava.
Tambora 1815- Indonesia, largest in recorded history.
71,000 people died from impact alone or starvation and
disease afterwards. Ruined agriculture and livestocklead to worst famine in 19th century.
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Krakato 1883- Indonesia. Produced tsunami with
waves reaching 120-140 ft. 40,000 people killed.
Loudest explosion- heard 3000 miles from origin.
Mt. Vesuvius 1979- Italy. Wipes out entire town.
Hundreds of years later everything and everyone
was found by archaeologists, perfectly preserved in
ash. 13,000 people died.
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Yellowstone-super volcano.
 Researchers
report the super-volcano underneath the
state of Wyoming has been rising at a record rate
since 2004. Its floor has gone up three inches per
year for the last three years indicating the fastest rate
since records began in 1923
 http://dsc.discovery.com/convergence/supervolcano/su
pervolcano.html
Earthquakes
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Movement of Earth’s lithosphere that occurs when
rocks in the lithosphere suddenly shift, releasing
stored energy.
Small portion of this energy is carried by vibrations
called seismic waves.
Stress in Earth’s Crust
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Stress- force that squeezes rocks together, stretches
or pulls them apart, or pushes them in different
directions.
As tectonic plates move, they cause stress in the
crust, which in turn produces faults and folds.
Fault- break in a mass of rock along which
movement occurs
Fold- bend in layers of rock
Faults and Folds
San Andreas Fault
Earthquake Fold in California
Earthquakes and Seismic Waves
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Earthquakes occur because stress forces have
exceeded the strength of rock.
The location beneath Earth where an earthquake
begins is called the focus.
Epicenter- location on Earth’s surface directly above
the focus.
As earthquake occurs, seismic waves move out in all
directions from the focus.
Types of Seismic Waves
P Waves- Primary Waves
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S Waves- Secondary Waves
Longitudinal waves similar
to sound waves.
Compress and expand the
ground like an accordion.
Particles move in direction
of waves.
Fastest seismic waves and
first to be detected at a
distance.
Travel in solids and liquids
.
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Transverse Waves like
light.
Particles move at right
angles to the direction
of the waves.
Cannot travel through
liquids.
P and S Waves
Surface Waves
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Waves that develop when seismic waves reach
Earth’s surface.
Move more slowly than P waves and S waves, but
usually produce larger ground movements and
greater damage.
Some are transverse waves and others have a
rolling motion similar to ocean waves.
Measuring Earthquakes
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Seismograph- record seismic waves to measure
and pinpoint their epicenters.
Richter Scale- rates earthquakes based on
measurements of the times and amplitudes of
seismic waves by certain seismographs.
Moment Magnitude Scale- most useful, gives a
measure of the amount of energy released.
Modified Mercalli Scale- ranges from 1-12 and is
based on observations in the areas affected.
Significant Earthquakes and
Environmental Impacts
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Permanent vertical or horizontal displacement of the
ground affects people, buildings, bridges, freeway
overpasses, dams, pipelines.
China 1976- 655,000 deaths
Haiti 2010- 316,000 deaths
Peru 1970- caused massive landslide that buried
the town of Yungay killing 17,000 people.
Tsunamis
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Large sea wave
generated by an
underwater
earthquake, volcano,
or landslide.
Significant Tsunamis and Environmental
Impacts
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March 11, 2011- Japan, earthquake that led to a
tsunami. Dead/missing is 22,000. Radioactive
material released into atmosphere.
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2004 Indian ocean earthquake that led to tsunami.
The earthquake was the result of the sliding of the
portion of the Earth's crust known as the India plate
under the section called the Burma plate. 228, 000
people died. Devastated many coastal areas.
Intact mangrove forests helped protect buildings and
people.
In Sri Lanka, greatest damage occurred where illegal
coral mining and reef damage had caused severe
beach erosion.
Areas affected by 2004 tsunami
Asia Tsunami Timeline
Questions
1. The hypothesis that the continents move slowly over
Earth’s surface is called?
2. New ocean crust is formed along?
3. What is a break in a rock mass along which
movement occurs?
4. The location where earthquake begins?
5. Cause Earth to vibrate in the direction of the
wave’s motion?