Chapter 6 Volcanoes

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Chapter 6 Volcanoes

• Volcanoes Plate Tectonics Volcanic
  ActivityVolcanoes in Idaho??? 
• http//www.youtube.com/watch?vbgRnVhbfIKQ

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Student Objectives

• Students will discuss where volcanoes generally
  form, specifically name the three types of
  locations, be able to draw picture showing how
  they form, and how it ties into plate tectonics.
• Students will distinguish between magma and lava
  and the three types of volcanoes.
• Students will also discuss how early volcanism
  changed the landscape of Idaho and describe its
  features.

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Volcanoes

• The Eruption of a volcano is among the most
  dangerous and awe inspiring events on earth!
• A volcano is a weak spot in the crust where
  molten magma comes to the surface.
• Magma is a mixture of molten rock-forming
  substance that includes gases, and water vapor
  from the mantle.
• When magma reaches the surface, it is called lava

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June 1991 Philippines Mt. Pinatubo
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Mt. Vesuvius The Unexpected!

• On August 23, 79 AD, Pompeii looked like any
  other busy, prosperous city. People were moving
  about, trading goods, news, and friendly talk.
• Three days later, on August 26, all of these
  sounds had fallen silent, and the place itself
  had vanished. Almost nothing was seen of Pompeii
  for more than 1500 years. Now, more than 1900
  years later, we are learning more and more about
  the last days of Pompeii.

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What happened to Pompeii preserved a treasury of
information about life in the ancient Roman
Empire. The ash and lava quickly ended their
lives and preserved their days
activities.These people below died instantly.
Their bodies decayed inside the rock and ash
tombs. Later, the hollowed areas were filled in
with minerals.
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Other Famous Volcanoes

• 1883 Indonesia Krakatau
• 1902 Martinique Mt. Pelee (29,000 killed)
• 1912 Alaska Mt Katmai
• 1991 Philippines Mt Pinatubo
• 1980 Washington Mt St. Helens
• Present - Kilauea - formed Caldera 1790
• Japan Mt Fuji erupted 16 times since 781 ad,
  most recent in 1708

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Location of Volcanoes

• There are about 600 active volcanoes on land.
  Many more lie beneath the sea.

Volcanoes occur in belts that extend across
continents and oceans, such as the Ring of Fire
in the Pacific Ocean.
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Volcanic Destruction!
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Several Different Locations of Volcanoes

• Volcanoes can be found at
• Convergent plate boundaries
• Divergent plate boundaries ? Hot spots

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FIRST TYPE LOCATIONVolcanoes at Convergent Plate
Boundaries

• Subduction causes slabs of ocean crust to be
  thrust down through a deep-ocean trench into the
  mantle. The crust melts and forms magma, which
  rises back toward the surface, erupting as lava.

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SECOND TYPE LOCATION Volcanoes at Diverging
Plate Boundaries

• Volcanoes form along the mid-ocean ridge, where
  new ocean crust is being formed and pushed in
  opposite directions.
• Only in a few places, such as Iceland and the
  Azores do the volcanoes of the mid-ocean ridge
  rise above the oceans surface.

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• Iceland is one the very few places where the
  mid-oceanic ridge rises above oceans surface.
• This is a common sight there!

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THIRD TYPE LOCATION Hot SpotVolcanoes

• A hot spot is an area where magma from deep
  within the mantle melts through the crust like a
  blow torch. Hot spots often lie in the middle of
  continental or oceanic plates far from any plate
  boundaries.
• Yellowstone marks a major hot spot. The last
  major eruption in Yellowstone was 75,000 years
  ago.

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Volcanic Activity

• Just like CO2 trapped in a can of pop, the
  dissolved gases are under lots of pressure.
• A volcano erupts when an opening develops in
  weak rock on the surface. The gases dissolved in
  the magma rush out, carrying the magma with them
  in an explosive display.

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830am May 18,1980 Mt St Helens
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Mt St. Helens

• Movie http//www.youtube.com/watch?vvBJ9xZws7r
  o

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This is the volcano named after me! (after an
episode a few years ago where students didnt
study for an important test!!!)
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Late March, 1986 Mt. Augustine
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Late March, 1986 Mt. Augustine
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Volcanism in Idaho??? Yellowstone Snake River

• The Snake River Plain extends 400 miles (650 km)
  westward from northwest Wyoming to the
  Idaho-Oregon border. The Snake River Plain is a
  broad, flat depression, which covers one
  quarter of the state of Idaho.

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The geysers, hot springs, and bubbling mud pots
of Yellowstone National Park indicate there is
extra heat beneath this corner of Wyoming.

• The heat is from a hot spot beneath Yellowstone
  that causes all the sensational features in
  Yellowstone.
• This hot spot used to be under Idaho!!

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• Yellowstone's Rocky Mountain splendor
• Thousands of steaming geysers, shimmering
  thermal pools, and bubbling mud pots are evidence
  of this hot spot activity

But the greatest wonder of all goes mostly
unnoticed.
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Whats going on in Yellowstone?

• Hidden underground, powerful volcanic, tectonic,
  and hydrothermal forces are continually reshaping
  the landscape of Yellowstone.
• Symptoms of the underground turmoil include
  numerous earthquakes (most too small to be felt),
  uplift and subsidence of the ground surface, and
  persistent but ever-changing hydrothermal
  activity.
• Eventually, the unrest will culminate in another
  large earthquake or volcanic eruption, both of
  which have occurred many times before in
  Yellowstone's geologic past.

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Calderas

• The largest and most explosive volcanic
  eruptions eject tens to hundreds of cubic
  kilometers of magma onto the Earth's surface.
  When such a large volume of magma is removed from
  beneath a volcano, the ground subsides or
  collapses into the emptied space, to form a huge
  depression called a caldera. Some calderas are
  more than 25 kilometers in diameter and several
  kilometers deep.

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Craters of the Moon is a volcanic field of old
calderas. Craters of the Moon had 8 eruptive
episodes from 15,000 to approximately 2,000 years
ago. Craters of the Moon lava field lies along
the northern border of the Snake River Plain.
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• Eight times in the past 15,000 years lava poured
  from cracks which opened along this weak spot in
  the earth's crust.
• Expanding gases in the lava ejected rocks
  hundreds of feet into the air.
• The tops literally were blown off (and the ash
  landed in Nebraska and Wyoming) resulting in the
  Idaho smiley face.

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• Beneath the crust of the Snake River Plain and
  into Yellowstone lies a "hot spot" or localized
  heat source.
• The hot spot does not move but rather remains in
  a fixed position.
• The crust of the earth moves over it as the
  North American plate slides southwestward over
  the hot spot.
• As the plate moves over the hot spot volcanic
  eruptions occur on the surface.

This picture shows how the plate moves over the
hot spot producing island arcs. Idahos caldera
were formed in a similar manner!
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• Initially these eruptions were very violent.
• Huge calderas of up to 30 miles in diameter were
  formed when these devastating eruptions took
  place.
• Later a more fluid lava flowed onto the surface
  and covered the crater, giving it the smoother
  texture that we see in the satellite photos.
• As you drive along the highway in southern Idaho,
  you are driving through these huge ancient
  Caldera!

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Idahos Calderas

• Calderas become progressively younger from west
  to east. The Yellowstone calderas are they
  youngest and mark the approximate location of the
  hotspot.

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Video 4 minutes long Watch all the different
kinds of lava flows Notice how the houses
instantly ignite when the lava comes
close Witness what happens to the highway when
the lava creeps across Why do you think the song
may be appropriate for the name Ring of Fire?

• http//www.youtube.com/watch?vESXWanLH7mUfeature
  related

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Do you know the answer?

• Where do volcanoes generally form?
• What are the three types of locations?
• How do volcanoes ties into plate tectonics?
• What is the difference between magma and lava?
• What are the three types of volcanoes?
• How do we know that Idaho had ancient volcanoes?
• What kind of volcano in the making is found
  under Yellowstone National Park?

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• A Volcanic Landscape The shallow arc of Idaho's
  Snake River Plain spans southern Idaho, gently
  rising from west to east. Current theories
  suggest that the plain marks the path of
  continental movement over a deep hotspot now
  lying beneath the Yellowstone Plateau. As the
  continent drifted southwestward over millions of
  years, calderassuper-volcanoes 10 - 40 miles (15
  - 64 km) wideerupted over the hotspot. When
  Yellowstone Caldera erupted 640,000 years ago, it
  released about 240 cubic miles (1,000 km3) of
  material, covering half of North America in 6
  feet (2 m) of debris.
• In the past 17 million years, there have been
  about a dozen catastrophic eruptions releasing
  huge volumes of rhyolitic magma and ash. Between
  these super-eruptions were long periods when more
  fluid basaltic lava flowed from more than 8,000
  shield volcanoes and numerous lava cones.
  Remnants of these dot the Eastern Snake River
  Plain today. Layer upon layer of basalt flows
  extend 3,000 - 6,000 feet (1,000 - 2,000 m) below
  the surface, completely covering the rhyolite
  "basement."
• 1. Sinking Rivers and a Flowing Aquifer Streams
  that flow here are indirect tributaries to the
  Snake River. The aptly named Lost River flows to
  an area known as "the sinks" where it soaks into
  the ground, becoming part of an aquifer the
  volume of Lake Erie. The aquifer flows through
  pores and fractures in the rock hundreds of feet
  beneath the surface, eventually emerging from
  springs along the Snake River Canyon at Thousand
  Springs about 100 miles (160 km) to the
  southwest.
• 2. Big Southern Butte Big Southern Butte, rising
  2,500 feet (760 m) above the Eastern Snake River
  Plain, is a prominent reminder of the region's
  volcanism. About 300,000 years ago, the butte
  intruded through surrounding layers of basalt,
  rising to an elevation of 7,560 feet (2,300 m).
  It is one of the largest composite rhyolite domes
  in the world.

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