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Chapter TWELEVE. Volcanoes. If green dots are earthquakes and red triangles are volcanoes, What are two things that you notice about their locations??. Section 1: Volcanoes and Earth’s Moving Plates. What Are Volcanoes?. A volcano is an opening in Earth that erupts gases, ash and lava.

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slide2

If green dots are earthquakes and red triangles are volcanoes,

What are two things that you notice about their locations??

section 1 volcanoes and earth s moving plates
Section 1: Volcanoes and Earth’s Moving Plates

What Are Volcanoes?

  • A volcano is an opening in Earth that erupts gases, ash and lava.
  • Volcanic mountains form when layers of lava, ash and other material build up around these openings.
section 1 volcanoes and earth s moving plates1
Section 1: Volcanoes and Earth’s Moving Plates

What Are Volcanoes?

  • Kilauea (kee low AY ah), located in Hawaii, is the world's most active volcano.
  • The most recent series of eruptions began in 1983 and still continues.
section 1 volcanoes and earth s moving plates2
Section 1: Volcanoes and Earth’s Moving Plates

How Do Volcanoes Form?

  • Magma is forced upward because it is less dense than the rock around it.
  • After many thousands or even millions of years, magma reaches Earth's surfaces and flows out through an opening called a vent.
section 1 volcanoes and earth s moving plates3
Section 1: Volcanoes and Earth’s Moving Plates

How Do Volcanoes Form?

  • As lava flows out, it cools quickly and becomes solid, forming layers of igneous rock around the vent.
  • The steep walled depression around a volcano's vent is called a crater.
section 1 volcanoes and earth s moving plates4
Section 1: Volcanoes and Earth’s Moving Plates

Where Do Volcanoes Occur?

  • Divergent Plate Boundaries
    • The mid-Atlantic ridge is an area where the plates are moving apart.
    • When plates separate, they form long, deep cracks called rifts.
    • Lava flows from these rifts and is cooled quickly by sea water.
section 1 volcanoes and earth s moving plates5
Section 1: Volcanoes and Earth’s Moving Plates

Where Do Volcanoes Occur?

  • Sometimes, the volcanoes and rift eruptions rise above sea level, forming new islands such as Iceland.
  • In 1963, the new island Surtsey was formed during a volcanic eruption.
section 1 volcanoes and earth s moving plates6
Section 1: Volcanoes and Earth’s Moving Plates

Where Do Volcanoes Occur?

  • Convergent Plate Boundaries
    • Forms volcanoes where an oceanic plate slides below a continental plate.
    • Magma forms when the plate sliding below another plate gets deep enough and hot enough to melt partially and the magma is then forced upward to the surface.
    • Volcanoes that form at convergent plate boundaries erupt more violently than other volcanoes do.
section 1 volcanoes and earth s moving plates7
Section 1: Volcanoes and Earth’s Moving Plates

Where Do Volcanoes Occur?

  • Hot spots
    • Form when areas between the Earth's mantle and core are unusually hot and rock at these areas is forced toward the crust where it melts partially.
    • Magma breaks through the crust to form several volcanoes.
    • Not at a plate boundary
    • Formed Hawaiian islands
section 2 types of volcanoes
Section 2: Types of Volcanoes

What Controls Eruptions?

  • Trapped gases like water vapor and carbon dioxide build up in volcanoes.
  • If the gas escapes easily, it is a quiet eruption.
  • If gas and water vapor build up, eruptions can be explosive
section 2 types of volcanoes1
Section 2: Types of Volcanoes

Composition of Magma

  • Quiet eruptions: magma that is low in silica and is basaltic.
    • Has lava that pours from volcanic vents and runs down the sides of a volcano
section 2 types of volcanoes2
Section 2: Types of Volcanoes

Composition of Magma

  • Explosive eruptions: magma that is high in silica and is andesitic.
    • Has magma that is thick and when pressure builds up an explosion occurs. It often carries pieces of lava.
section 2 types of volcanoes3
Section 2: Types of Volcanoes

Forms of Volcanoes

  • Shield Volcano
    • Broad, gently sloping volcano formed by quiet eruptions of basaltic lava.
    • The basaltic lava flows over Earth's surface covering large areas with deposits of basaltic igneous rocks when it cools.
section 2 types of volcanoes4
Section 2: Types of Volcanoes

Forms of Volcanoes

  • Shield Volcano
    • Accounts for the greatest volume of erupted volcanic material.
    • Much of the new seafloor that originates at the mid-ocean ridge forms as underwater flood basalts.
section 2 types of volcanoes5
Section 2: Types of Volcanoes

Forms of Volcanoes

  • Cinder Cone Volcano
    • Steep-sided, loosely packed volcano formed when tephra falls to the ground.
    • Tephra: bits of rock or solidified lava dropped from the air after an explosive eruption.
    • Vary in sizes from volcanic ash, cinders, large rocks and blocks.
section 2 types of volcanoes6
Section 2: Types of Volcanoes

Forms of Volcanoes

  • Composite Volcano
    • Volcano built by alternating explosive and quiet eruptions that produce layers of tephra and lava.
    • Found mostly where Earth's plates come together and one plate sinks below the other.
section 3 igneous rock features
Section 3: Igneous Rock Features

Intrusive Features

  • Batholiths: large intrusive rock body that forms when magma being forced upward toward Earth's crust cools slowly and solidifies underground.
  • Dikes: magma that is forced into a crack that cuts across rock layers and hardens.
  • Sills: magma that is forced into a crack parallel to rock layers and hardens.
section 3 igneous rock features2
Section 3: Igneous Rock Features

Other Features

  • Volcanic neck: solid igneous core of a volcano left behind after the softer cone has been eroded.
    • When a volcano stops erupting, the magma hardens inside the vent.
    • Erosion, usually by water and wind, begins to wear away at the volcano.
section 3 igneous rock features3
Section 3: Igneous Rock Features

Other Features

  • Caldera: large circular-shaped opening formed when the top of a volcano collapses.
    • Crater Lake in OR is a caldera that filled with water and is now a lake.
section 3 igneous rock features4
Section 3: Igneous Rock Features

Effects of Eruptions

  • Examples of destruction:
    • Lava flows destroy everything in their path.
    • Falling volcanic ash can collapse buildings, block roads and can cause lung disease in people and animals.
    • Volcanic ash and debris rush down the side of a volcano: pyroclastic flow.
section 3 igneous rock features5
Section 3: Igneous Rock Features

Effects of Eruptions

  • Examples of destruction:
    • Temperature inside a pyroclastic flow can be high enough to ignite wood.
    • Sulfurous gases from volcanoes can mix with water vapor in the atmosphere to form acid rain.
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In your notes, create a diagram of a volcano. It must include the following features (with correct lables):

  • Ash cloud
  • Pyroclastic flow
  • Tephra
  • Layers of ash
  • Layers of lava
  • Crater
  • Main vent
  • Dike
  • Sill
  • Magma chamber