GEOGRAPHY

24. (Question A2, Figure page 51). Most of the movement along the San Andres Fault occurs during earthquakes. An average movement of about 5 m (16ft) along the San Andres Fault was associated with the devastating 1906 San Francisco earthquake that killed people and destroyed property. Assuming that all displacement along the fault was produced by earthquakes of this magnitude, how many Earthquakes are needed to produce the displacement observed in the previous question? 1. ~1,000 2. ~10,000 3. ~65,000 4. ~100,000 Lab manual (Busch, 9th Edition) Activity 2.7: Plate tectonics of the Northwest United States Notice the ages of seafloor rocks in Figure 2.6. The modern seafloor rocks of this region are forming along a divergent plate boundary called the Juan de Fuca Ridge. The farther one moves away from the plate boundary, the older the seafloor rocks. 25. (Question B2, Figure 2.6). Notice the seafloor rocks older than 8 million years are present west of the Juan de Fuca Ridge but not east of the ridge. What could cause their absence from the map? They are absent because ______________. 1. a strike slip fault along the ridge has moved older rocks further north. 2. older rocks have been subducted underneath the North American Plate 3. rifting has produced metamorphism, which obliterated the old age of the seafloor 4. erosion of the sea floor destroyed rocks older than 12 million years 26. (Question B3, Figure 2.6) The type of plate boundary represented by the red line on the figure is a/n __________________ boundary. 1. transform 2. convergent 3. divergent 4. unconformity 27. (Question B4, Figure 2.6) Which of the following best explains the origin of magma that builds Cascade Range volcanoes? 1. As the North American Plate and the Juan de Fuca Plate slide past each other on a horizontal plane, friction produces the heat to generate magma. 2. As the Juan de Fuca plate is rifted apart, lower pressure at the rift produces magma that feeds the volcanoes at the Cascade Range. 3. Subduction of the Juan de Fuca Plate under the North American Plate brings rocks from the ocean floor and marine sediment to depths where partial melting ensues due to the increased temperature and the influence of water. 4. Migration of the North American Plate over a hot spot is responsible for the Cascade Range volcanoes. Part 2- Google Earth The exercises that follow use Google Earth. For each question (or set of questions) paste the location that is given into the “fly to” box. Examine each location at multiple eye altitudes and differing amounts of tilt. For any measurements use the ruler tool, this can be accessed by clicking on the ruler icon above the image. Google Earth: Hawaiian Islands Fly to Hawaii. Please review the section on Hotspots and the Hawaiian Islands in the Lab manual and in the unit notes. Rocks have been dated on each of the Hawaiian Islands and their ages are as follows: Big Island- 0 (active), Maui – 1.1 million, Kauai- 4.7 million, Nihoa (23 03 32.79N 161 55 11.94W)- 7.2 million years 28. Consider the ages and positions of the islands listed above along with what you know about plate tectonics and hotspots. In what general direction is the Pacific Plate moving? 1. Northwest 2. Southeast 3. Northeast 4. Southwest 29. How fast was the Pacific plate moving during the last 1.1 million years between the formation of the Big Island and Maui in cm/year? 1. ~5 cm/year 2. ~10 cm/year 3. ~15 cm/year 4. ~20 cm/year 30. How fast was the Pacific plate moving from 7.2 million years ago to 4.7 million years ago between the formation of Kauai and Nihao in cm/year? 1. ~5 cm/year 2. ~10 cm/year 3. ~15 cm/year 4. ~20 cm/year 31) Examine the headings of the measurements that you took for the previous two questions. The headings indicate the direction the Pacific Plate is moving over the hot spot. How does the direction of motion of the Pacific Plate during the last 1.1 million years differ from direction of movement between 4.7 and 7.2 million years ago? The direction of plate movement in the last 1.1 million years________. 1. shows no change 2. has become more northerly 3. has become more southerly 32) Zoom out and examine the dozens of sunken volcanoes out past Nihoa, named the Emperor Seamounts. As one of these volcanic islands on the Pacific Plate moves off the hotspot it becomes inactive, or extinct, and the island begins to sink as it and the surrounding tectonic plate cool down. The speed the islands are sinking can be estimated by measuring the difference in elevation (tilting the image helps to find the highest elevation) between two islands and dividing by the difference in their ages (this method assumes the islands were a similar size when they were active). Using Maui and Nihoa, how fast are the Hawaiian Islands sinking? 1. ~0.05 cm/year 2. ~0.5 cm/year 3. ~5 cm/year 4. ~10 cm/year 33) Using the speed you calculated in the previous question (and ignoring possible changes in sea level), when will the Big Island of Hawaii sink below the surface of the ocean? 1. ~650,000 years 2. ~1.2 million years 3. ~8 million years 4. ~13 million years 34) Examine the Emperor Seamounts and notice that it is a continuous chain that reaches far north to the Aleutian Islands of Alaska. Using a speed halfway between that which you calculated in questions 29 and 30, calculate the age of the oldest (furthest North) seamount in the Emperor Seamounts? (Hint 1- using the line mode of the ruler tool will not work since the Pacific Plate had a drastic change in direction, try using the path mode of the ruler tool to give a more accurate distance; Hint 2- Since you know the plate does not move at the same speed over time, the age you estimated will differ from the real age based on radiometric dating, therefore your answer will be different from the one given in the lab manual!). 1. ~30 million years 2. ~45 million years 3. ~60 million years 4. ~75 million years Google Earth: Identifying Plate Boundaries 35. Fly to 15 19 48.78 S 75 12 03.41 W. What type of tectonic plates are present? 1. Ocean- Ocean 2. Ocean- Continent 3. Continent- Continent. 36. What type of plate tectonic boundary is present? 1. Transform 2. Convergent 3. Divergent 37. Fly to 6 21 49.68 S 29 35 37.87 E. What type of process is going on at this location? 1. Seafloor spreading 2. Continental rifting 3. Subduction 38. What type of plate tectonic boundary is present? 1. Transform 2. Convergent 3. Divergent 39. Fly to 28 04 27.04N 86 55 26.84E. What type of tectonic plates are present? 1. Ocean- Ocean 2. Ocean- Continent 3. Continent- Continent. 40. What type of plate tectonic boundary is present? 1. Transform 2. Convergent 3. Divergent

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