INTRODUCTION: This lab exercise is designed to help you to move from viewing simple textbook diagrams of crustal deformation processes and landforms to recognizing and interpreting these elements in real landscape settings. You will Google Earth to view a number of specific locations within the United States that have folded or faulted landforms. Each location and landform that you visit is listed below and includes the name or coordinate of the location, some additional background information, and a series of questions to answer. Your learning goals in this exercise are to: 1) review learned knowledge of processes and landforms, 2) identify real topographic expressions of processes and landforms, thus practicing the terminology, and 3) critically analyze and interpret the processes that formed specific landforms using the Google Earth visualization and supporting information. INSTRUCTIONS: Turn on Google Earth. Type in the location in quotes or the indicated coordinates to find the landforms and answer questions about them. A. Fly to “Greybull, Wyoming” and explore Sheep Mountain just to the North. 1. What type of fold is this? 2. Zoom out and examine the surrounding area. What type of rock (Igneous, Sedimentary, or Metamorphic) is creating most of the landscape here? How can you tell (support your answer with visual evidence). B. Fly to “Moab, Utah” 1. Moab is located in a valley. Examine the valley by looking down its axis (tilt your view) and determine whether the valley is in the center of a syncline or anticline. How can you tell (support your answer)? The area around Moab, UT is known as the Colorado Plateau which was covered in a shallow sea for much of its history. As the seas evaporated, they left behind large deposits of salt. When under high confining pressure, for example if it is buried deeply under other sedimentary rocks, rock salt flows like wet putty or glacial ice toward areas of lower pressure. The salt can flow laterally or vertically until it encounters an area of less pressure such as a fault. Topographic bulges (anticlines or domes) can develop where salt flowage lifts overlying strata. 1 Figure 1. Moab Valley Salt Diapir (Baars and Doelling, 1987) C. Fly to the coordinates: 38°26’12.21”N, 109°55’46.65”W, just to the SW of Moab and between the Green and Colorado Rivers in Canyonlands National Park. Zoom out enough so that you can see the feature. 1. Describe this feature 2. What is this feature called 3. Think about the geologic history of nearby Moab that you just learned about in part B. How do you think this feature formed? D. Fly to Steens Mountain, Oregon. To the east of Steens mountain you’ll see the dry lakebed of the Alvord Desert. 1. Describe the Terrain between the top of Steens Mountain and the Alvord Desert. 2) Are the Steens Mountains eroding or accumulating sediment. In other words, are they a sediment source or sink? 2 3. Is the Alvord Desert eroding or accumulating sediment. In other words, are they a sediment source or sink? Rotate and tilt your view so that you are looking straight Steens Mountain from above the Alvord Desert and fly up and down the mountain front. You will notice that the mountain ridges perpendicular to the mountain front look like they’ve been lopped off leaving triangular shaped faces. These are called “triangular facets” or “faceted spurs” (Figure 2). Figure 2. Erosion of a tilted fault block produces a rugged mountain range. A line of triangular facets at the mountain base marks the position of the original fault plane. (Drawn by A. N. Strahler) 4. Zoom out to look at SE Oregon more broadly. Fly around and observe the terrain between Summer Lake (search for it if you don’t know where it is) and the Idaho border. Do you see other mountain ranges or valleys that have similar characteristics to Steens Mountain and the Alvord Desert? Name a few of them and describe the patterns you notice when looking at this landscape. 5. Based on your knowledge of different types of faults from lecture and reading, what type of fault do you think formed Steens Mountain? What observations above lead you to this conclusion? 3 5. What type of stress causes this fault? Steens Mountain is part of the Basin and Range region that extends from eastern Oregon/California across most of Nevada to Western Utah and parts of Arizona. Zoom out and look at the Basin and Range area – you’ll notice a similar patterns of alternating mountains and valleys across this entire region. 8. The Basin and Range is a result of continental extension. Draw a simplified cross section showing how continental extension creates faults that produces alternating mountains and valleys: (label Steens Mountain and the Alvord Desert in your sketch) 4 E. Now let’s go view some other big mountains. Fly to Chief Mountain, MT! Chief Mountain (and the mountains to the west that are part of the Rocky Mountains in Glacier National park) consists of older sedimentary rocks that have been faulted on top of younger sedimentary rocks. 1. Sedimentary rocks form in basins (lakes, valleys, oceans) or sediment ‘sinks’ as we’ve referred to them in this class. Because of the way they form, the older rocks are always located below the younger rocks. The orange line in the image represents a fault that pushed the older rocks on top of the younger ones. What type of fault can push younger rocks on top of older ones as observied at Chief Mountain? 2. What kind of stress is responsible for this type of fault? 5 3. Draw a simplified cross showing the type of fault you think is responsible: 4. How come these mountains don’t look exactly like your drawing of the simplified drawing of faults in your text/lecture? (hint: think about whats been happening to all these rocks over time as they are exposed to rain, snow, glaciers, rivers, etc…) E. Finally, let’s take a look at the San Andreas Fault in California. Fly to the coordinates: 35°06’45.87”N, 119°38’40.63”W. This is the Elkhorn Scarp area east of San Luis Obispo, CA, and the site of the often used photo of the fault (photo is viewing fault from the North). 1. Zoom out to about 10 miles and observe the fault. As you know from class, the San Andreas Fault is a classic example of what type of fault? 2. Scan back and forth across the fault near the Elkhorn Scarp and note that many rivers are flowing from the mountains in the NE toward the SW. Also note that many of these rivers become offset along the fault. This offset can tell you the relative motion of the fault. Is it right lateral or left lateral and how do you know? 6 7
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