Plate Tectonics

1. Plate Tectonics

2. Notes • Plate Tectonic Theory: • Geological theory that states that pieces of Earth’s crust are in constant, slow motion • Plate-section of the Earths crust that slowly moves over the mantle

3. Earths Plates

4. Three Types of Plate Boundaries • Divergent Boundary • Convergent Boundary • Transform Boundary

5. Divergent Boundary • Convection currents are spinning in opposite directions which begins to split the plate

6. Crust Crust Mantle

7. Rift Valley • When a continental plate begins to split a rift valley forms.

8. The Great African Rift

9. Process of Sea Floor Spreading • Once the plate is split in two, magma reaches the surface along the crack, cools, and creates new oceanic crust.

10. New crust Oldest Crust Older Crust Older Crust Oldest Crust Same Age Same Age

11. The plates continue to move apart creating an undersea mountain chain called a mid-ocean ridge.

12. New crust Mid Ocean Ridge

13. Convergent Boundary Where two plates come together. Converge = to move towards or meet at one point When two plates converge, the result is called a collision.

14. 1. Oceanic-Continental • Subduction occurs • Volcanic mountains on land are formed (Remember: Oceanic lithosphere is more dense than continental lithosphere.)

15. Example of Oceanic-Continental Convergence • Oceanic-continental convergence creates many of the Earth's active volcanoes, such as those in the Andes and the Cascade Range in the Pacific Northwest. Cascade Mountain Range

16. Mt. Rainier Mount St. Helens (pre-eruption) Mount Hood

17. 3 Types of Convergent Boundaries 2. Oceanic-Oceanic • Subduction occurs • Volcanic mountains under the sea are formed The density of the plates determines which plate sinks into the mantle.

18. Example of Oceanic-Oceanic Convergence Over millions of years, erupted lava and volcanic debris pile up on the ocean floor until a submarine volcano rises above sea level to form an island volcano. The Aleutian Islands (off of Alaska) are a chain of more than 300 small volcanic islands forming an island arc in the Northern Pacific Ocean.

19. 3. Continental-Continental • No subduction occurs. • Instead, the crust buckles and is pushed upward or sideways. • Mountains on land are formed.

20. Example of Continental-Continental Convergence • 50 million years ago, India collided into Asia • Eurasian Plate to crumpled up and over the Indian Plate • Slow continuous convergence over millions of years pushed up the Himalayas • Most growth occurred during the past 10 million years • The Himalayas, as high as 8,854m (5.50162 miles!) above sea level, form the highest continental mountains in the world Note: Mt. Rainier is only 4,392 m above sea level. Himalayas are over twice that!!!

21. Transform Boundary When two plates move past each other in opposite directions. • Earthquakes often occur along transform boundaries, but crust is neither created nor destroyed. • Also known as faults

22. Example of Transform Boundary San Andreas Fault in California

23. Let’s Review! • At divergent boundaries, plates move apart and new land forms. • At convergent boundaries, plates move towards each other, and if an oceanic plate is involved subducted occurs (pushed down) and the result is either volcanic islands (ocean-ocean) or volcanic mountains (ocean-continental). No oceanic plate is involved (two continental plates = no subduction and non-volcanic mountains). • At transform boundaries, plates slide past each other, and lithosphere is neither formed nor subducted.