Grade 7 Science Unit 4: The Earths Crust

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Grade 7 ScienceUnit 4 The Earths Crust

• Earthquakes, Volcanoes and Mountains

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Earthquakes

• The shaking of the Earth
• Measured using a seismograph
• The Richter Scale measures the strength of the
  earthquake

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• They are the result of energy released from
  forces built up due to plate tectonics in Earths
  crust
• When this energy is released, it travels in
  seismic waves.

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Local Earthquakes?

• Usually minor in our region. They occur due to
  the movement along local faults on the floor of
  the Atlantic Ocean.

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• Burin Peninsula, 1929, tsunami (pg. 374)

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Volcanoes

• An opening in Earths crust.

Mt. St. Helens May 18, 1980 Washington
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Paricutin February 20, 1943 Mexico
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Mt. Pinatubo June 1991 Philippians
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Kilauea November 24, 2007 Hawaii
The most active volcano on Earth
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Where Do Volcanoes Form?

• 1. At collision zones intense pressure can melt
  rock that later flows to the surface as a volcano
  (the Pacific Ocean is being subducted under Japan)

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• 2. Where plates separate, molten rock flows up to
  the surface (Mid-Atlantic Ridge)

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• 3. In area where the plates are thin, lava can be
  forced up through the cracks to the surface.
  (Hawaiian Islands)

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Pacific Ring of Fire

• The name given to the volcanoes encircling the
  Pacific Ocean.

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Activity 11-2E Patterns in Earthquake and
Volcano Locations

• Page 386-7

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• 2. Glooscap Mikmaq legend about the Sugarloaf
  Mountains.

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Theories and Explanations In the Past...

• 1. Pele Hawaiian goddess who makes the mountains
  shake and lava flow at Kilauea.

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• 3. Anaxagoras Greek who believed that volcanic
  eruptions were caused by great winds within the
  earth.

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• 4. René Decartes French philosopher who believed
  an incandescent earth core was the source of
  volcanic heat.

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Mountain Formation

• Due to
• 1. folding
• 2. faulting
• 3. volcanic eruptions.

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1. Folding...

• A bend in rock layers.
• Created when plates collide at convergent
  boundaries.

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Himalayan Mountains Asia
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Appalachian Mountains North America
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2. Faulting...

• A break in rock layers.
• When the rock is too brittle to fold.
• Faulting can result from squeezing or stretching
  the Earths crust.

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Andes Mountains South America
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3. Volcanic Eruptions

• When magma is forced up by pressure from deep
  within Earth, it can uplift the rock and create
  features on the surface. The magma may erupt as
  volcanoes.

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Mount St. Helens Washington