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Unit 4: Earthquakes & Volcanoes

Unit 4: Earthquakes & Volcanoes. AIM: How does stress in the crust change Earth’s surface?. Forces in Earth’s Crust. The movement of Earth’s plates creates enormous forces that squeeze or pull the rock in the crust. Stress – a force that acts on a rock to change its shape or volume.

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Unit 4: Earthquakes & Volcanoes

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  1. Unit 4: Earthquakes & Volcanoes AIM: How does stress in the crust change Earth’s surface?

  2. Forces in Earth’s Crust • The movement of Earth’s plates creates enormous forces that squeeze or pull the rock in the crust. • Stress – a force that acts on a rock to change its shape or volume. • Some rocks can become brittle and snap • Some rocks can bend slowly

  3. What are the 3 Types of Stress? • Tension, compression, and shearing work over millions of years to change the shape and volume of rock. • Tension: stretches rock so it becomes thinner • Occurs where 2 plates are moving apart.

  4. What are the 3 Types of Stress? 2. Compression: squeezes rock until it folds or breaks. • Occurs where 2 plates are colliding.

  5. What are the 3 Types of Stress? 3. Shearing: pushes a mass of rock in two opposite directions • Can cause rock to break and slip apart, or change its shape.

  6. Kinds of Faults • Fault – a break in the crust where rock surfaces slip past each other. • Most faults occur along plate boundaries.

  7. Kinds of Faults • Normal Faults: tension pulls crust apart – divergent • Fault is at an angle: • 1 block of rock lies above – hanging wall • the other lies below – footwall • Hanging wall slips downward Animation

  8. Normal Fault at Death Valley, California http://geotripper.blogspot.com/2008_02_01_archive.html

  9. Kinds of Faults 2. Reverse Faults: caused by compression • Same structure as normal fault, but rock moves in opposite direction • Hanging wall slides upward Animation

  10. http://rst.gsfc.nasa.gov/Sect2/Sect2_7.html

  11. Kinds of Faults 3. Strike-Slip Faults: plates move past each other sideways • Caused by shearing formed at transform boundaries Animation

  12. http://comp.uark.edu/~sboss/ex4s02answers.htm

  13. Changing Earth’s Surface • Folding – rock bends without breaking • Upward folds – anticline • Downward folds – syncline • Colliding plates can compress and fold crust over wide area • Produces largest mountain ranges • Ex: Himalayas in Asia “Folding” Video Clip

  14. Anticline-syncline pair in Silurian strata, Newfoundland, New Jersey. http://www.rci.rutgers.edu/~schlisch/structureslides/rte23folds.html

  15. Small-scale folding in stepping stones

  16. Changing Earth’s Surface 2. Stretching Earth’s Crust - two normal faults cut into rock • Parallel formation creates fault-block mountains Fault-Block mountains Video Clip

  17. Basin and Range

  18. Changing Earth’s Surface 3. Uplifting forces can raise plateaus • Large area of FLAT land elevated high above sea level • Forces in crust push up large, flat blocks of rock Plateau nearZion National Park, Utah

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