ENV 101 Ch04 lecture ppt_a
- 1. 4-1 Environmental Geology James Reichard Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.
- 2. 4-2 Chapter 4 Earth’s Structure and Plate Tectonics Amante, C. and B. W. Eakins, ETOPO1 1 Arc-Minute Global Relief Model: Procedures, Data Sources and Analysis, National Geophysical Data center, NESDIS, NOAA, U.S. Department of Commerce, Boulder, CO, August 2008.
- 3. 4-3 Deformation of Rocks (1) Elastic limit deformation becomes permanent Jump to long description
- 4. 4-4 Deformation of Rocks (2) (top): Courtesy of Phil Dombrowski; (bottom): © Jim Reichard Jump to long description
- 5. 4-5 Earth’s Interior Seismic waves • Travel at different speeds through different materials • Reflect and refract when density changes Jump to long description
- 6. 4-6 Earth’s Structure Crust – • Lithosphere < 15 km Mantle • ~2900 km thick • top is asthenosphere Outer core • liquid Inner core • solid Jump to long description
- 7. 4-7 Earth’s Magnetic Field • Inner core is solid, rotates faster than liquid outer core • Generates magnetic field National Geophysical Data Center/NOAA Jump to long description
- 8. 4-8 Earth’s Internal Heat • Geothermal gradient 25°C/km • Heat from radioactive decay of uranium, thorium, and potassium • Friction and pressure • Convection transfers heat Jump to long description
- 9. 4-9 Continental Drift Frank Taylor 1910 suggested the continents were once joined Alfred Wegener 1922 book on theory of continental drift • More evidence than Taylor • No mechanism
- 10. 4-10 Plate Tectonics NOAA Jump to long description
- 11. 4-11 Developing Theory of Plate Tectonics Mapping ocean floor • Mid Atlantic ridge Magnetic studies • Polar reversals Map location and depths of earthquakes • Fall on plate boundaries Polar wandering • Moving poles and continents supported data Jump to long description
- 12. 4-12 Mapping the Ocean Floor NOAA Jump to long description
- 13. 4-13 Magnetic Reversal NOAA Jump to long description
- 14. 4-14 Earthquake Locations Jump to long description
- 15. 4-15 Polar Wandering A. Fixed continents B. Moving continents Jump to long description
- 16. 4-16 Plate Tectonics and Earth’s Systems Plates • Rigid slabs in lithosphere Plate Boundaries • Plates move, slide past • Override • Tear • Smash into each other
- 17. 4-17 Plates Jump to long description
- 18. 4-18 Plate Boundaries Jump to long description
- 19. 4-19 Movement of Plates © Jim Reichard © Jim Reichard Jump to long description
- 20. 4-20 Surface Features & Plate Boundaries Divergent • Ocean ridges • Rift valleys Convergent • Oceanic-oceanic island arc • Oceanic-continental continental arc • Continental-continental mountain belt Transform Jump to long description
- 21. 4-21 Divergent Plate Boundaries (inset): NASA Jump to long description
- 22. 4-22 Convergent Plate Boundaries (1) (a-b): National Geophysical Data Center/NOAA NOAA Jump to long description
- 23. 4-23 Convergent Plate Boundaries (2) National Geophysical Data Center/NOAA NASA Jump to long description
- 24. 4-24 Transform Plate Boundry Jump to long description
- 25. 4-25 Plate Boundaries and People Natural hazards • Earthquakes, volcanic eruptions Natural resources Climate Development of life USGS Jump to long description
- 26. 4-26 The shifting position of continents affects Earth’s climate by altering the circulation of heat and water in the oceans. Jump to long description
- 27. 4-27 Allopatric Speciation due to a ocean trench Jump to long description
- 28. Appendix of Image Long Descriptions
- 29. Deformation of Rocks (1) Long Description A two-dimensional representation of the deformation (strain) that would result from different types of stress acting on a square. Jump back to slide containing original image
- 30. Deformation of Rocks (2) Long Description Rocks will deform elastically up to a point, beyond which deformation becomes permanent. Ductile materials deform permanently by flowing plastically, whereas brittle materials fracture. Rocks near the surface are typically brittle and will fracture, but when buried, the higher temperatures and pressures cause them to become ductile and deform plastically. Jump back to slide containing original image
- 31. Earth’s Interior Long Description Seismic waves generated by earthquakes and human-made explosions will reflect and refract when encountering layers of different density. Recording instruments measure the waves that return to the surface, enabling scientists to determine the depth of different layers all the way to Earth’s core. Jump back to slide containing original image
- 32. Earth’s Structure Long Description The Earth has a layered structure consisting of a high-density metallic core surrounded by a less dense rocky shell of silicate minerals, called the mantle. Near the top of the mantle the silicate minerals are close to their melting points, creating a weak and plastic zone called the asthenosphere. The outermost silicate shell is called the crust, which has the lowest density of all the layers. Geologists refer to the crust and uppermost mantle as the lithosphere since they behave as a single, rigid slab that moves over the asthenosphere. Note that the lithosphere in continental areas contains granitic crust, whereas basaltic lithosphere lies beneath the oceans. Jump back to slide containing original image
- 33. Earth’s Magnetic Field Long Description Earth’s strong magnetic field is believed to be the result of the metallic ions in the outer core circulating as the planet rotates. The magnetic field is important to the biosphere because it helps shield the Earth from harmful radiation streaming from the Sun. Jump back to slide containing original image
- 34. Earth’s Internal Heat Long Description Soon after Earth formed, enough heat was generated to cause the planet to become molten, with only a thin crust. Convection cells developed and began transporting both heat and matter to the surface, where some of the heat was lost to space by conduction—similar to that of a pot of boiling soup. Earth soon developed its layered structure as molten iron and nickel sank to the core and lighter elements tended to rise, eventually forming the crust and mantle. Jump back to slide containing original image
- 35. Plate Tectonics Long Description a) The distribution of unique plant and animal fossils on different continents (A) supports the idea of a single supercontinent. The matching fossil assemblages between South America and Africa were first noted by Alfred Wegener. The supercontinent called Pangaea (B) was originally proposed by Wegener, who suggested that the continents slowly drifted to their present position. Modern data show that Pangaea began to break up approximately 225 million years ago. b) The mismatch of glacial deposits and present day climates on several continents helped support the idea of continental drift. Jump back to slide containing original image
- 36. Developing Theory of Plate Tectonics Long Description A near-perfect fit of Africa and South America was obtained when the two landmasses were reassembled using the edge of their continental shelves as opposed to their coastlines. Jump back to slide containing original image
- 37. Mapping the Ocean Floor Long Description Modern map showing the topography of both the land and seafloor. One of the striking features of the oceans is the extensive network of mid-oceanic ridges that circle the globe, shown here in white. The oceans also contain narrow trenches that reach depths of nearly 7 miles (11 km). Jump back to slide containing original image
- 38. Magnetic Reversal Long Description a) Illustration showing the development of magnetic striping by seafloor spreading. Magma rises up through mid-oceanic ridges and then cools to form basaltic rocks whose magnetite grains record the orientation and polarity of Earth’s magnetic field. As the seafloor continues to spread and new rocks form, a symmetrical pattern of reverse and normal polarity develops on opposite sides of the ridge . b) Map showing the age in years before present (BP) and topography of the Atlantic seafloor. Note how the seafloor gets progressively older away from the mid-oceanic ridge, with the oldest seafloor being about 200 million years old. Jump back to slide containing original image
- 39. Earthquake Locations Long Description Map showing the location of earthquake epicenters from 1963 to 1998. Note how the earthquakes are not randomly distributed. Inset (A) illustrates how rising magma beneath mid-oceanic ridges generates earthquakes whose epicenters lie in a relatively narrow zone at the surface. Inset (B) shows how epicenters near ocean trenches are spread over a wider area due to the way the subducting slab generates earthquakes in an inclined zone. Jump back to slide containing original image
- 40. Polar Wandering Long Description When paleomagnetic studies assumed that the continents remained fixed (A), the position of the magnetic North Pole appeared to wander over time. Moreover, each continent showed a different wandering path for the pole. When seafloor spreading data were used to reposition the continents at different times in the geologic past (B), a single location for the pole emerged. Jump back to slide containing original image
- 41. Plates Long Description Map showing the distribution of lithospheric plates. Note how the North American plate is covered by both continental and oceanic crust, whereas the Pacific plate is covered entirely by oceanic crust. Jump back to slide containing original image
- 42. Plate Boundaries Long Description Illustration showing how divergent, convergent, and transform plate boundaries are under tension, compression, and shear forces, respectively. Note how mid-oceanic ridges and mountain chains are features that form parallel to plate boundaries. Volcanic hot spots occur away from plate boundaries and are believed to be related to hot plumes of material that rise from deep within the mantle. Jump back to slide containing original image
- 43. Movement of Plates Long Description a) Relationship between mantle convection cells and plate boundaries. Note how the plates move in the direction of the convection cells. b) A thick layer of snow on this car provides an example of the ridge push mechanism. Gravity caused the snow to push downward on the sloping surface of windshield, forcing the rest of the snow to slide over the hood. Note that the snow layer behaved as a rigid plate, allowing it to buckle, forming a fold. Also note that unfrozen water was present on the surface of the car, creating a weak layer that facilitated the movement of the overlying snow. Jump back to slide containing original image
- 44. Surface Features & Plate Boundaries Long Description Map showing the types of movement taking place at the boundaries of Earth’s major plates. Jump back to slide containing original image
- 45. Divergent Plate Boundaries Long Description Sequence of events showing the development of a midoceanic ridge system. A rising convection cell (A) pushes upward against the brittle lithosphere, creating tensional forces that cause the plate to fracture. This also creates a zone of lower pressure, causing melting of the asthenosphere and formation of magma. Continued tension (B) leads to faulting and the development of a rift valley where rising magma forms layers of basaltic rock. As the rift widens, it becomes flooded (C), forming a new ocean with a spreading center in the middle. Map showing the location of a young spreading center in eastern Africa. The northern portion of the rift zone has opened to a point where it has flooded, forming the Red Sea and Gulf of Aden. To the south is the much younger Great Rift Valley. Inset is a satellite photo showing the Sinai peninsula located at the top of the Red Sea. This peninsula is bounded on the left by the spreading center and by a transform boundary on the right. Jump back to slide containing original image
- 46. Convergent Plate Boundaries (1) Long Description a) The Aleutian Islands off the Alaskan mainland (A) are a narrow string of volcanic islands that represent a young island arc system. The much larger islands of Japan (B) represent a more mature island arc. Note the deep ocean trench in both examples, caused by the subducting plate on the ocean side of the island arc.“ "The Andes Mountains are a continental arc system associated with an oceanic-continental boundary. The boundary of these plates is marked by the position of the ocean trench. b) The Andes are the result of continued convergence and subduction of the oceanic plate, which has produced volcanic activity and numerous earthquakes. Jump back to slide containing original image
- 47. Convergent Plate Boundaries (2) Long Description a) The Himalaya Mountains are a modern example of the collision between two continental plates. As India moved toward the Asian landmass, the subduction of oceanic crust created a volcanic arc (A). After the two landmasses collided, the subduction zone eventually shut down and volcanic activity ceased. The collision continues to cause uplift and deformation today (B). b) Subduction does not occur along convergent boundaries involving two continental plates composed of relatively low-density material. Instead, the collision creates a thick zone of highly faulted and deformed mountains where the rocks undergo regional metamorphism. Photo shows the folded Zagros Mountains in Iran. Jump back to slide containing original image
- 48. Transform Plate Boundry Long Description The San Andreas fault is a transform boundary associated with the East Pacific Rise spreading center. The San Andreas forms the boundary between the Pacific and North Amercian plates. Note that just north of San Francisco, the western edge of North America changes from a transform to a convergent boundary that includes a subduction zone and volcanic arc. Jump back to slide containing original image
- 49. Plate Boundaries and People Long Description Aerial photo showing the San Andreas fault in Southern California, which forms the boundary between the North American and Pacific plates. Note how the stream channel has been offset due to recent movement along this transform plate boundary. Jump back to slide containing original image
- 50. The shifting position of continents affects Earth’s climate by altering the circulation of heat and water in the oceans. Long Description The shifting position of continents affects Earth’s climate by altering the circulation of heat and water in the oceans. Climate is also affected by the uplift of mountains and by the rates at which heat-trapping gases are released by volcanic activity and absorbed in the rock cycle. Jump back to slide containing original image
- 51. Allopatric Speciation due to a ocean trench Long Description The Wallace Line in Southeast Asia represents the boundary between distinctly different groups of plant and animal species. This boundary coincides with a deep ocean trench that forced species to evolve in isolation from one another on opposite sides of it. Jump back to slide containing original image