Earthquakes, Volcanoes, tsunamis by qxQF2o4


Integrated Science
   A mountain that forms when magma reaches the
   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
   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
   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
   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.

  Cindercones- 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
   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
   Quiet- very hot, low-silica magma generally erupt
     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
   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 livestock-
    lead to worst famine in 19th century.
   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.
   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

   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
   Stress- force that squeezes rocks together, stretches
    or pulls them apart, or pushes them in different
   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

   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             S Waves- Secondary Waves

   Longitudinal waves similar        Transverse Waves like
    to sound waves.
   Compress and expand the
    ground like an accordion.         Particles move at right
    Particles move in direction        angles to the direction
    of waves.
   Fastest seismic waves and
                                       of the waves.
    first to be detected at a         Cannot travel through
    distance.                          liquids.
   Travel in solids and liquids
P and S Waves
Surface Waves
   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
   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
   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.
   Large sea wave
    generated by an
    earthquake, volcano,
    or landslide.
Significant Tsunamis and Environmental
   March 11, 2011- Japan, earthquake that led to a
    tsunami. Dead/missing is 22,000. Radioactive
    material released into atmosphere.
   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
   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
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?

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