Chapter 3: Volcanoes

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Chapter 3 Volcanoes
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Chapter 3.1

• Key Concepts
• Where are Earths volcanoes found?
• How do hot spot volcanoes form?

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Definitions

• 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
  mantle.
• Lava when magma reaches the Earths surface.

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Volcanoes Plate Boundaries

• 600 active volcanoes on land, many more under the
  sea.
• 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.

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Volcanic belts form along the boundaries of
Earths plates
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• 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.

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Most volcanoes occur at

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

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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
  mountains.
• 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
  trench.
• Rock above the plate melts to form magma.
• Erupts to the surface as lava

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Volcanoes on Convergent Boundaries
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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
  Philippines

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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.

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Hot Spot Volcanoes

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

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Hot Spot Volcanoes

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

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Hot Spot Volcanoes

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

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3.2 PROPERTIES OF MAGMA

• 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.

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• Pahoehoe-fast moving, hot lava that has low
  viscosity
• 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.

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• 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
  questions.

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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

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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

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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

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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
  chamber
• Magma flows upward through a tube (pipe) that
  connects the magma chamber to the surface.

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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
  flow
• 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

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Content checkpoint think/pair sharetake two
minutes to answer these questions with a partner
nearby..

• 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?

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Kinds of Volcanic Eruptions

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

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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

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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
  explode
• Magma is pushed out of the vent with incredible
  force

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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

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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.

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Content checkpoint think-pair-share take two
minutes to answer these questions with a partner
nearby.

• 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

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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

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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?

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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.

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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

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

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

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

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

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• 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
  Idaho

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• Calderas
• Huge hole left by the collapse of composite
  volcanic mountains
• Filled with fallen pieces of the volcano, ash and
  lava
• 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
  caldera
• 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

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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
  layers
• Overtime ice, wind, or rain erode away the
  surrounding rock and expose the hardened magma

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• 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

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• 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

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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

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• 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
  ground
• The heated water and steam build up pressure
  until finally it erupts
• Ex) Old Faithful, Yellowstone National Park

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