1. 1 Natural Disasters Plate Tectonics & Physical Hazards Current Event--Mammoth Chile Earthquake Chile Tsunami

2. 2 Continental Drift – Geographic fit of continents – Fossils – Mountains – Glaciation Evidence supporting the idea that the continents had drifted Evidence supporting the idea that the continents had drifted. Researchers noted geographic fit of continentsResearchers noted geographic fit of continents e.g. Africa and S. Americae.g. Africa and S. America Atlantic formed by separation of Africa from S. AmericaAtlantic formed by separation of Africa from S. America Seuss, 1885, proposed super continent by studying fossils, rocks, mountainsSeuss, 1885, proposed super continent by studying fossils, rocks, mountains Wegener and Taylor, early 1900’s, proposed continental drift and PangaeaWegener and Taylor, early 1900’s, proposed continental drift and Pangaea

3. 3 Continental Drift – Geographic Fit Continents seem to fit like pieces of a puzzle

4. 4 Continental Drift - Fossils Similar distribution of fossils such as Mesosaurus

5. 5 Continental Drift – Mountain Ranges Mountain ranges match across oceans

6. 6 Continental Drift - Glaciation Grooves left by glaciers indicate location of glaciers and direction of movement Past glaciation indicates position of paleocontinents

7. 7 Problem with Continental Drift Alfred Wegener Presented hypothesis to other professionals Did not provide plausible mechanism to explain how continents driftedDid not provide plausible mechanism to explain how continents drifted

8. 8 New Theory Developed – Seafloor Spreading Harry Hess suggested new seafloor is created at mid- ocean ridges and destroyed in deep ocean trenches

9. 9 Seafloor Spreading Continental drift reexamined in 1960’s with new information Supporting evidence for seafloor spreadingSupporting evidence for seafloor spreading –Earthquakes –Volcanos –Age of Seafloor –Paleomagnetism

10. Evidence for Seafloor Spreading World Seismicity Earthquake distribution matches plate boundaries

11. Evidence for Seafloor Spreading Volcanism Volcanoes match some plate boundaries; some are hot spots

12. Evidence for Seafloor Spreading Age of Seafloor Youngest sea floor is at mid-ocean ridge Oldest sea floor away from mid-ocean ridge

13. 13 Seafloor Spreading - Paleomagnetism Earth’s magnetic field reverses approx. every 600,000 years As seafloor spreads, normal and reverse polarities are preserved in the rock record When rocks cool at the Earth’s surface, they record Earth’s magnetic field Earth has a magnetic field

14. 14 Seafloor Spreading – Age of Seafloor Young rocks (red) found near mid-ocean ridges (MOR) Away from MOR, age of seafloor gets progressively older (blue)

15. 15 What Drives Plate Motion? Convection Currents Air heats up, expands, and rises As air moves away, it cools, contracts, and sinks

16. 16 Mechanism for Seafloor Spreading Convection Currents –As heat rises, it moves away at spreading centers pulling plates apart –Plates slide over asthenosphere –The upper mantle then cools and becomes more dense – sinking at ocean trenches

17. 17 Plate Tectonics Theory John Tuzo Wilson combined ideas of Continental Drift and Seafloor Spreading into “Plate Tectonics”

18. 18 Earth’s Structure Earth’s internal structure – Chemical Composition – Physical Property

19. 19 Earth’s Structure Chemical Composition Layers divided by its composition –Crust Continental crust – Granite (2.8 g/cm 3 ) Oceanic Crust – Basalt (3.0 g/cm 3 ) –Mantle Composed of Fe & Mg –Core Composed of Fe & Ni Two parts –Outer core –Inner core

20. 20 Earth’s Structure Physical Properties Layers divided into rigid, plastic, or liquid –Lithosphere Rigid –Asthenosphere Plastic –Mesosphere Rigid –Outer Core Liquid Layer –Inner Core Solid Layer

21. 21 Lithospheric Plates Comprise approx. 12 large plates and 12 smaller plates Lithospheric plates are rigid layers that flow over a partially molten (plastic) asthenosphere

22. 22 Plate Boundaries Divergent Convergent Transform Where plate boundaries meet...

23. 23 Divergent Plate Boundary Boundaries where plates pull apart New crust is being formed

24. 24 Divergent Examples East Africa Rift ZoneMid-Atlantic Ocean Ridge

25. 25 Convergent Plate Boundary Plates move toward each other (collide) Crust is being destroyed Three types: –Ocean-continent –Ocean-ocean –Continent-continent

26. 26 Ocean-Continent Collision Produce volcanic arc system

27. 27 Ocean-Continent Examples Cascade Ranges – Northern California, Oregon, and Washington (left) –Form as oceanic crust collides with continental crust Mount St. Helens, Washington (right)

28. 28 Ocean-Ocean Collision Form a chain of island arc volcanoes

29. 29 Ocean-Ocean Examples Japanese Islands –Form along a trench as two oceanic plates collide –Mount Fuji (right) active volcano in Japan –Mount Ontake Erupts- 9\14Mount Ontake Erupts- 9\14

30. 30 Continental-Continental Collision Continental crust have same densities –Neither plates sink (subduct) –Form high mountain chains

31. 31 Continental-Continental Examples Himalayas – home of Mount Everest (highest mountain in the world)

32. 32 Transform Plate Boundaries Plates slide past one another Crust is neither created nor destroyed

33. 33 Convergent Boundary Examples San Andreas Fault –Runs almost the entire length of California

34. 34 Hot Spot Volcanism Hot spot volcanoes around the world Site of mantle plumes from deep within the core- mantle boundary Lithospheric plates slide over hot spots leaving a chain of dormant (not active) volcanoes

35. 35 Hot Spot Examples Formation of a volcanic island chain as oceanic plate moves over a stationary hot spot The age of the islands increases toward the left New islands will continue to form over the hot spot –Loihi will be the next island in the chain