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Plate Boundaries

Plate Boundaries. Plate Boundaries. Sea-Floor Spreading Harry Hess discovered that magma was rising on the sea floor causing it to spread. The hot magma rising in the mantle caused the spreading on the sea floor and the large pieces of crust (tectonic plates) to move.

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Plate Boundaries

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  1. Plate Boundaries

  2. Plate Boundaries Sea-Floor Spreading Harry Hess discovered that magma was rising on the sea floor causing it to spread. The hot magma rising in the mantle caused the spreading on the sea floor and the large pieces of crust (tectonic plates) to move. Continental Drift Theory Alfred Wegener developed the theory that the continents drift. At the time he did not know the mechanism that made this happen. Theory of Plate Tectonics These two theories lead to the Theory of Plate Tectonics.

  3. Plate Boundaries Plate Tectonics is the theory that Earth's outer crust (lithosphere) is divided into several plates that glide over the plastic-like and less ridged asthenosphere (upper mantle).

  4. Plate Boundaries What is the engine that moves the plates? Convection Currents • Transfers energy in the mantle • Causes the hotter magma in the mantle to rise • Causes the cooler magma in the mantle to sink

  5. Plate Boundaries Continental Crust • Layer of rock which forms the continents • Also forms shallow sea beds close to shore (continental shelf) • Floats on top part of the mantle (asthenosphere) • Older than oceanic crust, mostly granite rock • Thicker and less dense than oceanic crust

  6. Plate Boundaries Oceanic Crust • A thin layer of crust that underlies the ocean basins. • Consists mainly of basalt. • Younger than continental crust. • More dense than continental crust.

  7. Quick Action – INB Template Complete the table as you move through the PowerPoint Presentation. Glue into your notebook as a reference.

  8. Plate Boundaries What happens at plate boundaries? Plates do one of 3 things. • Converge (colliding or coming together) • Diverge (dividing or moving apart) • Transform (sliding past each other) Converge (destroys crust) Diverge (creates crust) Transform (neither destroys or creates crust)

  9. Quick Action – Plate Boundaries Ready for a song? The melody is to the “Adam’s Family.” Converging is colliding, Diverging is dividing, Transform is sliding, We are the plate boundaries. Dah na na na. <Snap, Snap> Bet you can’t get that out of your head!

  10. Plate Boundaries Divergent boundaries – dividing or moving apart • Two oceanic crusts diverge and create a mid-ocean ridge (mountains under the ocean). • This process is call sea-floor spreading. • New crust is created. The Mid-Atlantic Ridge actually comes above the ground in Iceland.

  11. Plate Boundaries Divergent boundaries – dividing or moving apart • Two continental crusts diverge and create a rift valley. • New crust is created. • Example is the Great Rift Valley in Africa • Over millions of years water will eventually fill the valley.

  12. Plate Boundaries Transform boundaries • Plates slip sideways past each other creating earthquakes. • Crust is neither created or destroyed. • Many of these boundaries are found on the sea floor. • The most famous transform boundary is the San Andreas fault in California.

  13. Plate Boundaries What happens when plates converge or collide? • Continental/Continental = folded mountains (Himalayas). • Continental/Oceanic = volcanoes form (Cascades in Oregon and Washington) • Oceanic/Oceanic = Volcanic arc of islands form(Aleutian Islands in Alaska)

  14. Plate Boundaries Converging boundary -continental/continental boundary. • Two continental crusts collide and push against each other. • This pressure causes both plates to rise creating folded mountains. • Not a subduction zone Himalaya Mountains

  15. Plate Boundaries Converging boundary - continental/oceanic boundary • The ocean crusts goes below the continental crust because its more dense. • Volcanoes form on the continent. • A trench forms at the place when the plates collide. • Subduction zone Cascade Volcanoes in WA, OR and CA Old crust is destroyed

  16. Plate Boundaries Converging boundary - oceanic/oceanic boundary • Two oceanic crusts collide and push against each other. • The older crust goes below the other one and creates a volcanic arc of islands. • Subduction zone Aleutian Islands in Alaska Old crust is destroyed

  17. Quick Action – INB Template

  18. Plate Boundaries Ring of Fire • A long chain of volcanoes that surround the Pacific Ocean. • One of the most geologically active area on Earth. • Site of frequent earthquakes and volcanic eruptions. • Caused by plate boundaries converging, diverging and transforming.

  19. Check for Understanding Can you… • Explain plate tectonics? • Name the three types of plate boundaries and describe their movement? • Relate plate boundaries to the formation of crustal features: such as mountains, trenches, volcanoes and ridges?

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