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Chapter 3: Volcanoes


Chapter 3: Volcanoes Chapter 3.1 Key Concepts: Where are Earth s volcanoes found? How do hot spot volcanoes form? Definitions: Volcano: a weak spot in the Earth s ... – PowerPoint PPT presentation

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Title: Chapter 3: Volcanoes

Chapter 3 Volcanoes
Chapter 3.1
  • Key Concepts
  • Where are Earths volcanoes found?
  • How do hot spot volcanoes form?

  • Volcano a weak spot in the Earths crust where
    molten material (magma) comes to the surface
  • Magma a molten mixture of rock forming
    substances, gases and water from the earths
  • Lava when magma reaches the Earths surface.

Volcanoes Plate Boundaries
  • 600 active volcanoes on land, many more under the
  • Volcanoes occur in belts that extend across
    continents and oceans.
  • Ring of Fire - major volcanic belt formed by the
    many volcanoes that rim the Pacific Ocean.

Volcanic belts form along the boundaries of
Earths plates
  • Volcanic belts form along the boundaries of the
    Earths plates
  • Diverging (? ?)and converging (??) occur.
  • Results in fractures in the Earths crust
  • Magma reaches the surface.

Most volcanoes occur at
  • Divergent Boundaries
  • Mid Ocean Ridge
  • Convergent boundary
  • Points of subduction
  • ex. Mount Etna Eurasian and African plates

Volcanoes on Divergent Boundaries
  • Under ocean point of Mid ocean ridges occurring
    ( long underwater mountain ranges)
  • Many have rift valleys down the center
  • Lava pours out of rift valley creates new
  • Land - Great Rift Valley in East Africa

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Volcanoes on Convergent Boundaries
  • Volcanoes form when
  • Two oceanic plates collide
  • Oceanic and continental plates collide
  • In both situations, oceanic plates sink beneath a
  • Rock above the plate melts to form magma.
  • Erupts to the surface as lava

Volcanoes on Convergent Boundaries
Volcanoes on Convergent Boundaries
  • Magma less dense than the surrounding rock
  • Magma rises to the surface and breaks through the
    ocean floor creating volcanoes.
  • String of islands formed Island arc
  • Examples Japan, New Zealand, Indonesia, the

Hot Spot Volcanoes
  • Hot Spot an area where material from deep
    within the mantle rises and melts forming magma
  • Volcanoes form above a hot spot when magma erupts
    through the crust and reaches the surface.

Hot Spot Volcanoes
  • Some hot spots lie in the middle of plates far
    from plate boundaries.
  • Others occur on or near plate boundaries.

Hot Spot Volcanoes
  • A hot spot in the ocean floor can gradually form
    a series of volcanic mountains
  • Ex. The Hawaiian islands

Hot Spot Volcanoes
  • A hot spot can also form under continents
  • Ex. Yellowstone National Park, WY

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  • Vocabulary
  • Element-a substance that cannot be broken down
    into other substances
  • Compound-a substance made of two or more elements
    that have been chemically combined
  • Physical Property-a characteristic of a substance
    that can be observed or measured without changing
    the composition of a substance
  • Chemical Property-any property that produces a
    change in the composition of matter.

  • Pahoehoe-fast moving, hot lava that has low
  • aa-higher viscosity, slower moving, cooler lava
    that Pahoehoe
  • Viscosity-the resistance of a liquid to flow
  • Silicamajor ingredient in magma made of silicon
    and oxygen.

  • Magma Composition
  • Magma varies in composition and is classified
    according to the amount of silica it contains.
  • The graphs show the average composition of the
    two types of magma. Use the graphs to answer the

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  • What materials make up both types of magma?
  • Silica, oxides, and other solids
  • Which type of magma has more silica? About how
    much silica does this type of magma contain?
    Rhyolite, 70
  • A third type of magma has a silica content that
    is halfway between that of the other two types.
    About how much silica does this type of magma
    contain? 60
  • What type of magma would have a higher viscosity?
    Explain. The rhyolite forming would have higher
    viscosity because it contains more silica

Volcanic Eruptions 3.3
  • Objectives
  • Explain what happens when a volcano erupts.
  • Describe 2 types of volcanic eruptions
  • Identify stages of volcanic activity
  • What comes out of volcanic explosions?
  • Ash, lava, steam, rock, gases, dirt

Volcanic Eruptions 3.3
  • Magma forms in the asthenosphere
  • Convection currents in the mantle bring magma
    towards the surface
  • Magma tries to flow into any open crack
  • When magma reaches a weak spot in the crust, a
    volcano forms
  • Lava is magma that has reached the surface

Magma Reaches Earths Surface
  • Volcanoes are systems of passage ways through
    which magma moves.
  • Inside a Volcano
  • Magma collects below the volcano in the magma
  • Magma flows upward through a tube (pipe) that
    connects the magma chamber to the surface.

Magma Reaches Earths Surface
  • Inside a Volcano
  • Gas and magma leave through vents
  • Central vent is the opening at the top
  • Side vent anywhere along the side of the volcano
  • Lava pours out of the vents and creates a lava
  • A bowl shaped area called a crater may form
    around the central vent

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Magma Reaches Earths Surface
  • A Volcanic Eruption
  • Dissolved gases are trapped
  • in magma under extreme
  • pressure (CO2 in a soda bottle)
  • as magma flows , pressure because there
    is less rock on top of it.
  • the dissolved gases expand and form bubbles
  • When a volcano erupts, the force of the expanding
    gas forces magma up the pipe until it explodes
    out the vent

Content checkpoint think/pair sharetake two
minutes to answer these questions with a partner
  • What common everyday occurrence can we relate to
    a volcanic eruption?
  • What happens to the pressure in the magma as it
    rises toward the surface?

Kinds of Volcanic Eruptions
  • Volcanic eruptions can be quiet or explosive.
  • Eruptions depend on the properties of magma
  • Silica content
  • Viscosity

Kinds of Volcanic Eruptions
  • Quiet Eruptions
  • Magma has low silica content low viscosity
  • Magma flows easier so gases bubble out gently
  • Lava can flow many kilometers from the vent
  • Produce both pahoehoe and aa lava
  • Example Hawaiian Islands Mount Kilauea

Kinds of Volcanic Eruptions
  • Explosive Eruptions
  • Magma has high silica content high viscosity
  • Magma doesnt always flow out of vent and so it
    builds up (like a cork in a bottle)
  • Trapped gases build up pressure until they
  • Magma is pushed out of the vent with incredible

Kinds of Volcanic Eruptions
  • Explosive Eruptions
  • Lava breaks into fragments that cool quickly and
    harden into different sizes
  • Ash fine, dust sized particles of lava
  • Cinders pebble sized particles
  • Bombs baseball to car sized chunks of lava
  • Pyroclastic flow when an explosive eruption
    hurls out gases, ash, cinders and bombs.
  • Pumice forms when lava cools quick and traps air
    bubbles inside
  • Obsidian forms when lava cools quick leaving the
    surface smooth and glass-like

Kinds of Volcanic Eruptions
  • Volcano Hazards
  • Quiet eruptions cause lava to flow far ---
    burning and burying everything in its path
  • Explosive eruptions can bury entire towns in ash,
    cause landslides, avalanches, cause damage from
    gases and cinders/bombs.

Content checkpoint think-pair-share take two
minutes to answer these questions with a partner
  • What is pyroclastic flow?
  • How does volcanic ash cause damage?
  • What is the main difference between a quiet
    eruption and an explosive eruption?

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Stages of Volcanic Activity
  • Life Cycle of a Volcano
  • Scientists use historical records and monitor
    volcanoes to determine what stage of activity a
    volcano is in
  • A volcano can be active, dormant or extinct
  • An active volcano is erupting or showing signs of
    near future eruptions
  • A dormant (sleeping) volcano can awaken in the
    future and become active
  • An extinct (dead) volcano is unlikely to erupt
    ever again

Stages of Volcanic Activity
  • Monitoring Volcanoes
  • Geologists use tiltmeters to detect slight
    changes in surface elevation cause by magma
    moving underground
  • They monitor gases escaping from a volcano
  • Increase in temperature might mean magma is
    nearing the surface
  • The changes detected may give a short warning
    time BUT
  • We cannot be certain the type of eruption or how
    powerful it will be

Think and Discuss.
  • Which is more likely to be dangerous a volcano
    that erupts frequently or a volcano that has been
    inactive for a hundred years? WHY?

3.4 Volcanic Landforms
  • Objectives
  • List the landforms that lava and ash create
  • Explain how magma that hardens beneath earths
    crust creates landforms
  • Identify other distinct features that occur in
    volcanic areas
  • Volcanic activity on and beneath the surface has
    built up Earths land areas.

Landforms from Lava and Ash
  • Volcanic eruptions create landforms made of lava,
    ash and other materials
  • Shield volcanoes
  • Cinder cone volcanoes
  • Composite volcanoes
  • Lava plateaus
  • Another landform results from the collapse of a
    volcanic mountain
  • caldera

  • Shield volcanoes
  • Gently sloping mountains
  • Thin layers of low viscosity lava build up over
  • Ex) the Hawaiian Islands
  • CSAV Hawaii Pele's Hair (Volcanic Glass) -
  • Kilauea Lava Flows on May 6, 2012 - YouTube

  • Cinder cone volcanoes
  • High viscosity lava produces ash, cinders and
  • Those materials build up around the vent in a
    steep cone shaped hill/mountain.
  • Ex) Sunset Crater in Arizona

  • Composite Volcanoes
  • Form when volcanoes alternate between quiet lava
    flows and explosive eruptions of ash, cinders and
  • Tall, cone shaped mountain with alternating
    layers of ash and lava
  • Ex) Mt St. Helens, Washington and Mt. Fuji, Japan

  • Composite Volcanoes
  • Form when volcanoes alternate between quiet lava
    flows and explosive eruptions of ash, cinders and
  • Tall, cone shaped mountain with alternating
    layers of ash and lava
  • Ex) Mt St. Helens, Washington and Mt. Fuji, Japan

  • Lava Plateaus
  • Low viscosity lava flows out of several long
    cracks and travels far before cooling
  • After millions of years a high plateau forms
  • Ex) Columbia Plateau in Washington, Oregon and

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  • Calderas
  • Huge hole left by the collapse of composite
    volcanic mountains
  • Filled with fallen pieces of the volcano, ash and
  • Enormous eruptions may empty the pipe and the
    magma chamber
  • there is only hollow space left that cant
    support the weight and it collapses on itself
  • Overtime water from rain and snow may fill the
  • Ex) Crater Lake, Oregon

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  • Soil from lava and ash
  • People settle near volcanoes because of the rich,
    fertile soil
  • At first, after volcanic eruptions the land is
    empty and barren
  • Overtime the ash breaks down and provides
  • Potassium
  • Phosphorus
  • Other substances that plants need

Landforms from Magma
  • Sometimes magma forces its way through cracks in
    the crust but never reaches the surface
  • The magma cools and hardens within the rock
  • Overtime ice, wind, or rain erode away the
    surrounding rock and expose the hardened magma

  • Volcanic Necks
  • Forms when magma hardens in the pipe
  • Overtime the outer rock is weathered away
  • Looks like a giant tooth
  • Ex) Ship Rock, New Mexico

  • Dikes and Sills
  • Dike when magma forces its way across multiple
    rock layers and hardens
  • Sill when magma squeezes between horizontal
    layers of rock and hardens
  • Ex) Palisades, NY NJ

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  • Batholiths
  • Large masses of rock that are formed when a huge
    mass of magma cools inside the Earths crust
  • The outer layers of rock erode away leaving the
    hardened magma exposed
  • Ex) Sierra Nevada Batholith

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  • Dome Mountains
  • Created by smaller bodies of magma
  • The hardened magma uplifts the surrounding rock
    and causes it to bend into a dome shape
  • Ex) Black Hills, South Dakota

Geothermal Activity
  • Geo Earth, therme heat
  • Geothermal activity when magma a few km beneath
    the surface heats underground water.
  • Ex) hot springs and geysers found near past and
    present volcanic activity

  • Hot Springs
  • Forms when underground water is heated by magma
    or hot rock
  • The heated water rises and collects in pools

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  • Geysers
  • Fountains of water and steam that erupt from the
  • The heated water and steam build up pressure
    until finally it erupts
  • Ex) Old Faithful, Yellowstone National Park

  • Geothermal Energy
  • Heated water can provide an energy source
  • Heated water can be used to power turbines and
    create electricity
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