Original Source: sites.tenafly.k12.nj.us/~plobosco/

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Volcanoes

• Original Source sites.tenafly.k12.nj.us/plobosc
  o/

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Volcanoes and Earths Moving Plates

• Objectives
• To describe how volcanoes can affect people.
• To discuss the conditions that cause volcanoes.
• Identify the relationship between volcanoes and
  Earths moving plates.

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Volcanoes

• A volcano is an opening in the Earth that erupts
  gases, ash and lava.
• Kilauea is the worlds most active volcano.

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Lava

• When the magma reaches the surface, it is called
  lava. The place in the Earths surface through
  which magma and other materials reach the surface
  is called a volcano. In some places, lava can
  build up to form a cone-shaped mountain.
• The opening from which lava erupts is the vent.
  Volcanoes often have more than one vent.

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Formation of a Volcano

• The opening where lava flows out is a vent.
• The steep walled depression around the vent is a
  crater.

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Volcanoes

• Volcanoes can be both destructive and
  constructive forces.

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Destructive Effects of Eruptions

• Lava destroys everything in its path. Ash can
  cause lung damage.
• If ash and debris run down the side of the
  mountain, this is called a pyroclastic flow.
  Temperatures in this flow can be hot enough to
  ignite wood.
• Sulfurous gases can mix with water vapor and form
  acid rain that kills plants and animals.

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Constructive Effects of Eruptions

• The soil formed from volcanoes is very fertile
  and will eventually lead to abundant plant
  growth.
• The sulfur in volcanic vents along the ocean
  floor allow life to exist without sunlight
• Volcanoes recycle earths minerals

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Where do Volcanoes occur?

• Volcanoes form along divergent plate boundaries,
  convergent boundaries and hot spots.

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Divergent Plates

• Volcanoes often form where plates are moving
  apart, such as the Surtsey in Iceland.
• Iceland is located on the Mid Atlantic Ridge.

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Convergent Plate Boundaries

• Soufriere Hills On the Island of Monserrat is an
  example of a volcano that formed when one plate
  slide under another and melted.
• The magma was forced up and formed a volcano.

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Hot Spots

• Some volcanoes form over hot spots in the mantle.
  
• These are not on a plate boundary but in the
  center of a plate.
• The Hawaiian Islands formed over a hot spot in
  the Pacific Plate.

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Types of Volcanoes

• Objectives
• To discuss how explosiveness of a volcano is
  related to the silica and water content.
• To discuss the three types of volcanoes.

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Magma

• Deep within the Earth, under tremendous pressure
  and at great temperatures, rock exists as a hot
  liquid called magma. This molten rock is found
  in pockets called magma chambers.

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What Controls Eruptions?

• Eruptions are controlled by
• 1) the amount of trapped gas and the water vapor
• 2) how much silica is present in the magma

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Trapped Gas

• As magma reaches the surface, it is under less
  pressure. Gas can escape. Gas escapes easily
  during quiet eruptions.
• If gas build up to high pressure this will cause
  an explosive eruption.

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Amount of Water Vapor

• The magma at some convergent boundaries contains
  a lot of water vapor.
• This is because oceanic plate material and some
  of its water slide under other plate material at
  some convergent plate boundaries.
• The trapped water vapor in the magma can cause
  explosive eruptions.

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Viscosity of Magma

• Magma is divided into two major types silica
  rich and silica poor
• The greater the silica content, the more viscous
  or thick the magma.

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Basaltic Magma

• Magma that is low in silica is called basaltic
  magma. It is fluid and produces quiet flows such
  as those at Kiluea.
• Basaltic lava flows under water produce pillow
  lava formations.

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Basaltic Lava

• Pahoehoe (p-hoi-hoi) forms a smooth, billowy,
  ropelike surface.
• Aa, flows at a lower temperature, is stiff and
  slow moving.

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Andesitic Magma

• Andesitic magma is more rich in silica than
  basaltic magma but it has less silica than
  granitic magma.
• It forms at convergent boundaries where one plate
  slides under the other.
• It is more explosive than basaltic magma.
• Krakatau was mainly andesitic in composition.
  The word andesitic comes from the Andes Mountains.

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Granitic Magma

• This type of lava is light in color. This lava,
  has high water content and high silica content.
  Light-colored lava causes explosive eruptions.
  Silica hardens in the vents and form rocks.
  Steam and new lava build up under the rocks.
  When the pressure becomes great, a violent
  explosion occurs. When this type of lava cools on
  the surface it forms the igneous rock, rhyolite,
  which resembles granite.

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Gaseous Lava

• When lava that contains large amounts of gases,
  such as steam and carbon dioxide, hardens it
  forms rocks with many holes in them, due to the
  gas bubbles.
• Pumice and scoria are igneous rocks formed from
  this type of lava.

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3 Types of Volcanoes

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

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Cinder Cones

• They are steep sided cones of basaltic fragments
  and are smaller and simpler than composite
  volcanoes.
• Streaming gases carry liquid lava blobs into the
  atmosphere that fall back to earth around a
  single vent to form the cone.
• The volcano forms when ash, cinders pile up
  around the vent to form
• a circular or oval cone.
• Most common kind of volcano

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http//www.k12.hi.us/kapunaha/student_projects/vo
lc_blowout/cinder_cone_volcano.htm
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Tephra

• Explosive eruptions throw lava and rock high into
  the air. Bits of rock or solidified lava dropped
  from the air are called tephra.
• The smallest particles are called volcanic dust.
  (less than 0.25 mm)
• Volcanic Ash ( 0.25 -5mm) falls to the Earth and
  forms small rocks.
• Cinder (5mm-a few cm)
• Volcanic bombs (a few cm to several meters) are
  molten and harden as they travel through the air.

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Paricutin Volcano in Mexico
http//4.bp.blogspot.com/-x6k8MObhuIg/T0vD-JmMSxI/
AAAAAAAAGv8/myMqukEGkwk/s1600/paricutin.jpg
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Shield Volcanoes

• Volcanoes composed of quiet flows are called
  shield volcanoes.
• Because it is runny, 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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Mauna Loa, Hawaii Earths Largest Volcano
http//hvo.wr.usgs.gov/maunaloa/4303062_M.jpg
http//hvo.wr.usgs.gov/maunaloa/
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Flood Basalts

• Basaltic lava can also flow onto Earths surface
  through large cracks called fissures.
• This type of eruption forms flood basalts
• Columbia Plateau was formed as the lava spread
  out over the ground.

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Composite Volcanoes (Stratovolcano)

• Most deadly
• 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.
• Lower slope is gentle, but they rise steeply
  toward the summit

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Composite Volcano (Stratovolcano)
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Mount Vesuvius (near Naples, Italy)
http//www.history.com/topics/pompeii/videos
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Mount St Helens
http//dsc.discovery.com/tv-shows/discovery-presen
ts/videos/understanding-volcanoes-mt-saint-helens.
htm
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Krakatau

• One of the most violent eruptions in recent times
  occurred on an island in the Sunda Straits neat
  Indonesia in 1883.
• 36,000 people were killed.
• The island fell into the magma chamber.
• http//www.history.com/shows/how-the-earth-was-mad
  e/videos/the-krakatoa-volcanothe-krakatoa-volcano
  

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Igneous Rock Features

• Objectives
• To describe intrusive rock features.
• To explain how a volcanic neck and a caldera form.

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Predicting Volcanoes

• There are four indicators of volcanic activity
• Rising magma (increase in electric current)
• Seismic activity (tremors)
• Ground deformation
• Changes in gases (carbon dioxide and sulfur
  dioxide)

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Instruments used to Detect Volcanic Activity

• Tiltmeters are sensors that use laser beams to
  help create map of the physical changes in the
  earths surface that rising magma causes.
• Scientists also measure the levels of gases
  escaping, such as carbon dioxide and sulfur
  dioxide.
• Gravimeters measure the electrical currents given
  off by magma. An increase indicates a rise in
  the level of magma
• The most recent development uses satellites to
  detect heat from the gases released by volcanoes.
• The satellite Landsat uses infrared sensors.

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Limits of Seismography in Detecting Volcanic
Activity

• Seismographs cannot determine magma height, depth
  or how fast the magma is rising.

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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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Intrusive Igneous Rock Features

• Most magma never reaches the surface.
• Much of it hardens in the earth.
• Sometimes the hardened magma becomes exposed at
  the surface.
• These rock bodies are called intrusive igneous
  rock features.
• Examples are batholiths, sill, dikes and volcanic
  necks.

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Batholiths

• The largest intrusive igneous rock bodies are
  called batholiths. They form when magma bodies
  that are being forced upward cool and solidify
  before reaching the surface.

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Yosemite National Park

• The granite domes of Yosemite National Park are
  exposed batholiths.

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Sills and Dikes

• Magma sometimes squeezes into cracks below the
  surface.
• Magma that cuts across rock layers and hardens is
  called a dike.
• Magma that is forced into a crack parallel to the
  rock layers and hardens is a sill.

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Volcanic Neck

• When a volcano stops erupting, magma will harden
  inside the vent.
• Erosion wears away the outside of the volcano and
  the solid igneous rock in the vent remains.
• Ship Rock in New Mexico was formed this way.

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Calderas

• Sometimes after an eruption, the top of a volcano
  can collapse. This produces a large depression
  called a caldera.
• Crater Lake in Oregon is a caldera that filled
  with water and is now a lake.

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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 whether
  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 is an example of a dormant volcano in the
  United States.
• Scientists can be wrong. Mount St. Helens was
  considered to be dormant but erupted after long
  periods of inactivity.

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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.

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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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Ring of Fire
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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.
• Under the ocean, there is 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
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