Earthquakes, Volcanoes, and Tsunamis

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Earthquakes, Volcanoes, and Tsunamis
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Earthquakes

• Fault a break in the Earths crust.
• Blocks of the crust slide past each other along
  fault lines.
• When rocks that are under stress suddenly break,
  a series of ground vibrations is set off.
• These vibrations are known as earthquakes.
• Earthquakes are occurring all the time.

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Focus Epicenter

• The point beneath the surface where the rocks
  break and move is called the focus. The focus is
  the underground origin of an earthquake.
• Directly above the focus, on the Earths surface
  is the epicenter. Earthquake waves reach the
  epicenter first. During an earthquake, the most
  violent shaking is found at the epicenter.

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Seismologists

• Seismologists study earthquakes. They can
  determine the strength of an earthquake by the
  height of the wavy line recorded on the paper.
• The seismograph record of waves is called a
  seismogram.
• The Richter scale is used to calculate the
  strength of an earthquake.

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The Richter Scale

• Used by scientists to quantify the amount of
  energy released by an earthquake.
• Magnitude The measure of the energy released by
  an earthquake.
• The scale goes from 1.0 to 10.0.
• Each increase of magnitude by one whole number is
  ten times greater and releases 31.7 times more
  energy than the whole number below it.

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The Seismograph

• A weight attached to a spring remains nearly
  still even when the Earth moves. A pen attached
  to the weight records any movement on a roll of
  paper on a constantly rotating drum. The drum
  moves with the Earth and affects the line.

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Seismic Risk Map of the U.S.
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Tsunamis

• Earthquakes which occur on the ocean floor
  produce giant sea waves called tsunamis.
  Tsunamis can travel at speeds of 700 to 800 km
  per hour. As they approach the coast, they can
  reach heights of greater than 20 meters.

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How a Tsunami Forms
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Volcanoes

• A volcano is a mountain built from magma.
• Magma melted rock that found beneath the surface
  of the earth (called lava when above earths
  surface)
• Located near tectonic plate boundaries where
  plates are sliding or separating from one
  another.
• May occur on the land or under sea.

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Formation of a Volcano
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Volcanic Eruptions

• A volcano erupts when the pressure of the magma
  inside becomes so great that it blows open the
  solid surface of the volcano.
• Some volcanoes have magma flowing out of them all
  the time so the pressure never builds up and they
  never erupt.

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Local Effects of Volcano Eruptions

• Volcanic eruptions can be devastating to local
  economies and can cause great human loss.
• Clouds of hot ash, dust, and gases can flow down
  the slope of a volcano up to 200 km/hour and sear
  everything in their path.
• Volcanic ash can mix with water and produce a
  mudflow.
• Ash that falls to the ground can cause buildings
  to collapse, bury crops, damage engines, and
  cause breathing problems.
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Types of Volcanoes

• Different types of volcanic eruptions form
  different types of volcanoes.
• Cinder cones
• Shield volcanoes
• Composite volcanoes

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Global Effects of Volcano Eruptions

• Can change Earths climate for several years.
• Clouds of volcanic ash and sulfur-rich gases can
  reach the upper atmosphere. Iceland
• Ash and gas spread across the planet and reduce
  the amount of sunlight that reaches the Earths
  surface.
• Reduced sunlight can result in a decrease in the
  average global temperature over a period of
  several years.

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Ecological Functions of Earthquakes and Volcanoes

• Movement of the tectonic plates is an important
  part of recycling the planets crust.
• This helps form mineral deposits and promote and
  sustain life.
• Volcanic eruptions have played a key role in
  forming the atmosphere and climate of the Earth.

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Three Types
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Cinder Cones

• Volcanoes made mostly of cinders and other rock
  particles that have been blown into the air are
  called cinder cones. Cinder cones form from
  explosive eruptions. Because the material is
  loosely arranged, the cones are not high. The
  have a narrow base and steep sides such as
  Paricutin in Mexico.

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Cinder Cone Volcano
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Shield Volcanoes

• Volcanoes composed of quiet flows are called
  shield volcanoes. Because it is rummy, the lava
  flows over a large area. After several
  eruptions, a dome-shaped mountain is formed such
  as Mauna Loa (4km over sea level) in the Hawaiian
  Islands.

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Shield Volcanoes
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Composite Volcanoes

• Volcanoes built up of alternating layers of rock
  particles and lava are called composite
  volcanoes. During the formation of a composite
  volcano, a violent eruption first occurs, hurling
  volcanic bombs, cinder and ash out of the vent.
  Then a quiet eruption, produces lava flow that
  covers the rock particles. After alternating
  eruptions, a cone-shaped mountain forms such as
  Mount Vesuvius.

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Mount Vesuvius
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Mount Vesuvius

• Images of victims in eruption of Vesuvius in 79
  AD. Most died as a result of suffocation.

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Composite Volcano
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Crater

• There is often a funnel-shaped pit or depression
  at the top of a volcanic cone. This pit is
  called a crater. If the crater becomes very
  large as a result of the collapse of its walls,
  it is called a caldera. A caldera may also form
  when the top of a volcano explodes or collapses.

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Volcanic Crater
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Volcanic Activity

• Volcanoes are rather unpredictable . Some erupt
  regularly, others have not erupted in modern
  history. Scientists classify them as active,
  dormant or extinct.

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Active Volcanoes

• An active volcano is one that erupts wither
  continually or periodically such as Mount Katmai
  in Alaska and Mount St. Helens in the Cascade
  Range.

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Dormant Volcano

• A volcano that has been known to erupt within
  modern times but is now inactive is classified as
  a dormant volcano. Mount Rainier in Washington
  state are example of dormant volcanoes in the
  United States.

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Extinct Volcano

• A volcano not known to have erupted within modern
  history is classified as an extinct volcano.
  They have been worn away almost to the level of
  their magma chamber. Scientists can be wrong.
  Mount St. Helens was considered to be dormant but
  erupted after long periods of inactivity.

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Volcano and Earthquake Zones

• Most major earthquakes and volcanic eruptions
  occur in three zones of the world. Scientists
  believe that there is a great deal of movement
  and activity in the Earths crust in these three
  zones.

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Ring of Fire

• One major earthquake and volcano zone extends
  nearly all the way around the edge of the Pacific
  Ocean. This zone goes through New Zealand, the
  Philippines, Japan, Alaska and along the western
  coasts of North and South America. The San
  Andreas fault is part of this zone.

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Mediterranean Zone

• A second Major earthquake and volcano zone is
  located near the Mediterranean Zone and extends
  across Asia into India. Many countries in the
  zone, including Italy, Greece and Turkey, have
  violent earthquakes. Many volcanic eruptions
  also occur in this zone.

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Mid-Atlantic Ridge Zone

• The third major earthquake and volcano zone
  extends through Iceland and to the middle of the
  Atlantic Ocean. There is under the ocean a long
  range of volcanic mountains called the
  Mid-Atlantic Ocean Range. Scientists believe
  that the volcano and earthquake activity are due
  to the formation of new parts of the Earths
  crust along the ridge. The volcanic island of
  Iceland is part of this zone.

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Earthquake Belts