The Physical Earth Chapters 13 and 20 Living in the Environment , 11 th Edition, Miller

1. The Physical EarthChapters 13 and 20Living in the Environment, 11th Edition, Miller Advanced Placement Environmental Science La Canada High School Dr. E

2. Genesis of Earth Earth is 4.6 billion years old. • Same age as all other planets and the sun. Earth formation. • Nebular hypothesis. Diffuse cloud of matter rotating in space, formed a disk shaped body, which later formed into sun and planets. Planets are cooled and condensed gases that surrounded the sun.

3. Distribution of Elements • More than 100 elements in entire Earth, but 99% of Earth's mass is made up of only 8 elements Whole Earth: • Fe>O>Si>Mg>Ni>S>Ca>Al (others constitute < 1%) Earth's crust • O>Si>Al>Fe>Mg>Ca>K>Na (other constitute <1%)

4. Composition of Earth’s Crust Earth’s Crust Oxygen 46.6% All others 1.5% Magnesium 2.1% Silicon 27.7% Potassium 2.6% Sodium 2.8% Calcium 3.6% Iron 5.0% Aluminum 8.1% Fig. 10.4, p. 213

5. Crust: • Continental crust (20-70 km) • Oceanic crust (~6 km) • Mantle • Upper mantle • Lower mantle (660km - 2900 km) • Core • Outer core (liquid) • Inner core Earth’s Internal Structure: Compositional Layers

6. Earth Structure Mechanical layers • Inner and outer core • Mesosphere (lower mantle) • Asthenosphere - warm, ductile, weak, mantle beneath lithosphere • Lithosphere - cold, brittle, strong, uppermost crust and mantle

7. http://www.cotf.edu/ete/modules/msese/earthsysflr/rock.html

8. Igneous • Rock formed by cooling and crystallization of magma • If the cooling occurs at the surface, it is called extrusive igneous • If the cooling occurs in the Earth, it is called intrusive igneous • Extrusive igneous usually cools fairly rapidly and therefore has smaller crystals than intrusive • Examples: Granite, Basalt, Quartz, Mica, Feldspar, Obsidian http://hvo.wr.usgs.gov/hazards/dds24167_L.jpg

9. Sedimentary Rock • Rock formed by the piling of material over time • Sediment is compressed, heated and chemically changed over long period of time • Examples: Sandstone, Shale, Gypsum, Limestone, Chalk http://realgar.mcli.dist.maricopa.edu/alan/pix/grand-canyon.jpg

10. Metamorphic Rock • Igneous or sedimentary rock subjected to tremendous pressure and heat • Examples: Slate, Marble, Quartzite

11. Lithosphere • Lithosphere is divided into plates (7 major plates and about 16 plates). • Consists of rigid, brittle crust and uppermost mantle.

12. … Movement of these plates influences climate and evolution.

13. Evidence for Continental Drift • Coastline fit • Alignment of mountain ranges • Similar Rock Sequences • Fossils • Modern Fauna • Ancient climates

15. Plate Boundaries • Defined by earthquake data. • Depths of earthquakes indicate types of boundaries.

16. There are 3 types of plate boundaries • Convergent plate boundaries: when plates collide • Subduction: one plate of crust slides beneath another • Magma erupts through the surface in volcanoes, forming volcanic mountain ranges (the Cascades in Washington). • Two colliding plates of continental crust may lift material from both plates. • Resulted in the Himalaya and Appalachian mountains

17. Divergent plate boundaries: magma surging upward to the surface pushes them apart, creating new crust as it cools and spreads • Transform plate boundary: two plates meet, slipping and grinding alongside one another

18. Oceanic Divergent Boundary • Processes of extension, fracturing, crustal thinning, and magmatism. • Mid-ocean ridges are thermal bulge - lithosphere thin and hot at ridge. • Oceanic lithosphere cools and sinks as it moves away from ridge.

19. Oceanic Divergent Boundary • Extrusion of basaltic magma at spreading centers (decompression melting) • Shallow extensional earthquakes associated with mid-ocean ridges • Ocean drilling confirms that rocks get older away from mid-ocean ridges • Examples: Mid-Atlantic Ridge, East Pacific Rise

20. Convergent Boundaries • Crust destroyed at convergent margins, mountain building • Three types: • Ocean-Ocean • Ocean-Continent • Continent-Continent

21. Ocean-Ocean Convergent Boundaries • Deep oceanic trenches

22. Ocean-Ocean Convergent Boundaries • Documented by "missing" magnetic stripes (part of ocean crust has been subducted) • Deep-sea trench in front of accretionary wedge (scaped off oceanic rocks: greenstone blocks, blueschists, deep-sea sediments) • Volcanoes form above decending slabs • Dense root of island arc => magmas rise efficiently • Island arcs => arcuate chains of volcanic islands • Examples: Aleutians, Marianas, Island of Java, Indonesia

23. Ocean-Continent Boundaries • Heat added to crust by magmas causes regional and contact metamorphism • Heat added also produced more felsic magma types by crustal assimilation/fractional crystallization • Stratovolcanoes built on continental crust => continental volcanic arc • Deep-sea trench and accretionary wedge (melange) along coast of continent • Examples: Andes, Cascades, Central America

24. Ocean-Continent Boundaries • Magmas produced in mantle wedge above subducting slab • Much ascending magma stalls in continental crust -> batholith (roots of volcanic arc)

25. Transform Boundaries • Most fracture zones connect segments of mid-ocean ridges • Areas of different water depth on each side of fracture zone • Shallow earthquakes occur on transforms between sections of mid-ocean ridge

26. Transform Boundaries • Connect other plate margins (convergent and divergent) • San Andreas Fault - on land transform (Pacific plate sliding north relative to North America)

27. Hot Spots • Columns of hot material rising through mantle (plumes). • Source seems to be core-mantle boundary area (D" layer) - low velocity zones in lower mantle • Hot spot fixed in position underneath moving lithospheric plates

29. Hot Spots • Islands associated with hot spots (island chains, mid-ocean ridges, triple junctions). • Iceland (mid-ocean ridge). • Galapagos Islands (triple junction). • Island of Hawaii (mid-plate volcanic chain; hot spot trace). • Linear island chains form as plate moves over hot spot. • Hawaiian islands get older in direction of plate movement (older away from mid-ocean ridge).

30. Earth’s Magnetic Field • Liquid outer core consists of iron • Produces dynamo • Produces magnetic field • Dipolar magnetic field • Bar magnet • Reversals of magnetic field over time • Produces magnetic polarities in rock – Rock magnetization

32. Driving Forces of Plate Tectonics • Plate movement due to Earth's attempt to lose internal heat • Conduction • *Convection

33. Earthquakes Most destructive forces on Earth. But it is buildings and other human structures that cause injury and death, not the earthquake itself 1988 - Soviet Armenia: magnitude 6.9, 25,000 people died 1985 - Mexico City: magnitude 8.1, 9500 people 1989 - Loma Prieta, CA: magnitude 7.1, 40 people died 1995 - Kobe, Japan: magnitude 7, ~6000 people died

34. 30,000 earthquakes occur worldwide annually that are strong enough to be felt Typically only 75 of them are considered to be significant

35. Vibration of earth produced by rapid release of energy (seismic waves) with radiate in all directions from the source (focus) • Like ripples from dropping a stone in a pond, energy dissipates with distance • Earthquakes don't occur randomly. Occur on faults or fractures within the earth • Explained by plate tectonics. Most occur on plate boundaries • Sometimes in plate interiors if enough stress is built up

36. Elastic Rebound Theory • Forces bend rock on either side of fault • Rock strains ever so slowly • Weakest point breaks • Break sends out shock waves, which migrate outwards from he original break, causing shaking • Stress is released • Aftershocks are adjustments to that change in stress • Always less strong than the main shock, but they may cause more damage to weakened structures

37. Duration of Shaking • 1989 Loma Prieta: 15 seconds • 1960 San Francisco: 40 seconds • 1962 Alaska: 4 minutes!!!!

38. Types of Waves Earthquake waves = seismic waves. Recorded on seismometers on seismographs. Types of Waves • Surface waves - travel on Earth's surface, away from epicenter. • Very slow waves. Cause a lot of damage, rolling feeling at end of earthquake • Body Waves - travel through Earth's interior, spread outward from focus

39. Body Waves P waves: • Pressure or compressional waves. Vibrate parallel to direction of wave travel like a slinky. • Fast travel: 4-7 km/sec (15,000 mph) • P is primary, or first wave to arrive at recording station S waves: • Shear waves. Vibrates perpendicular to direction of wave travel. Like snapping a rope • Slower than P wave: 2-5 km/sec (11,000 mph) • So S is secondary, or second wave to arrive at recording station

41. Locating the Epicenter of an Earthquake • P, S and surface waves all start out at same time. • The further you are away from the quake, the longer the time span between arrival of P and S wave. • The distance of the seismometer to the earthquake can be determined by the time between the arrival of P wave and arrival of S waves. • Can tell the distance, but not the direction. • Therefore, multiple sites must be used to find epicenter.

45. Volcanoes • Located at plate boundaries & EQ zones (why ?) • Result in surface pyroclastic and extrusive rocks • Pyroclastic : particles thrown into air during eruption - settle to form ash, tuff & agglomerate • Magma extruded to surface to form extrusive igneous rocks (lava), e.g rhyolite, andesite & basalt (type depends on acidity) • Acidic : viscous, flows poorly • Basic : more fluid - flows on very gentle slopes over vast areas, e.g basalt plains of Victoria

46. Volcanoes • Basic parts of a volcano • Crater (depression at the summit of a volcano, connected by a vent or pipe to the magma chamber below) • Caldera (crater more than 1 km in diameter, formed at the summit of a volcano when lava is drained from an underground magma chamber, causing the summit of the volcano to be unsupported, and to collapse)

48. Types of Volcanoes 1. Shield volcanoes - Hawaii • Docile lava outpouring. Only minor pyroclastic material • Lava forms broad dome with central crater • Slope is 2-10 degrees, like flattened shield • Very long lived, very large, massive amounts of lava (pahoehoe and aa) Example: Kilauea

49. 2. Cinder cones • Erupt pyroclastic material • Steep slopes (30 to 40 degrees) • Not very long lived. • Typically small, less than 1000 feet tall • Often parasitic on larger volcanoes Examples: Paricutin in Mexico, Sunset crater in Arizona

50. 3. Composite volcanoes • Erupt lava and pyroclastic material • Intermediate slopes because lava acts like protective coating on pyroclastic layers • Built up over long periods of time • Most picturesque, but most violent Examples: Mt. Vesuvius, Mt. Shasta, Mt. Fuji, Yellowstone