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 Streams and Rivers Assessment

 Introduction

Over the past two weeks we have be using Google Earth as a tool to visualise and interpret a variety of landscapes. This assessment exercise is designed for you to demonstrate your learning by analysing some fluvial landscape features on both Earth and Mars.

The learning objectives of this exercise are listed below. You should ensure that your answers address these topics.

• Identify different drainage patterns, and draw or sketch your observations;
• Explain the relationship of drainage patterns to underlying geology/tectonics;
• Identify locations of erosion and deposition, and explain the relationship of these locations to the morphology of the river;
• Identify river/stream terraces and explain how these features form;
• Compare/contrast two different river systems and explain why they are different;
• Apply the concepts discussed for terrestrial fluvial systems to similar-looking systems on Mars, and thus interpret how these systems may have formed.

EXERCISE 1: TERRESTRIAL RIVERS

1. Locate Oxbow Bend by double-clicking its placemark. This feature is part of the Snake River in Grand Teton National Park, Wyoming. Make some careful observations of this feature by zooming in and out, rotating the view and using the 3D terrain perspective. Use these observations to answer the following questions.

• What type of river is this? What characteristics have you used to determine this?         2 marks
• Discuss briefly the processes of erosion and deposition that are occurring in this area. Where do they occur? Why do they occur in these specific locations?                                                            4 marks
• What will eventually happen to Oxbow Bend if this stream system continues to evolve? Is there any evidence of this particular process operating in the past along this portion of the Snake River? If so, describe the evidence and include a labelled snapshot of it (Edit > Copy Image). If not, describe the evidence you would have expected to see but did not.                                                          3 marks

2. Open the Oxbow Bend panorama. You can do this directly in Google Earth by clicking the Enter panorama link in the Places panel (you may have to click it twice). Please note that the panorama should appear as a circular overlay in this case. Zoom in and out of the pan as needed and change your perspective by clicking and dragging the mouse. When you are done, click Exit Photo in the top right-hand corner to return to the regular Google Earth view. You can also view the panorama via the webpage http://www.gigapan.org/gigapans/31360 – use fullscreen to get a better view. This option may be preferable if your computer struggles a bit with the Google Earth overlay.

• Consider the processes of erosion and deposition you observed in Question 1. What evidence of these processes can you find in the panorama?                                                                     2 marks
• Observe the morphology (overall shape) of the Snake River plain as seen in the pan, and get a broader view by using the terrain perspective in Google Earth. The river plain extends from the foreground out to the base of the Tetons in the distance. You can get a broad view of the river plain from the Tetons here: http://www.360cities.net/image/the-summit-of-the-grand-teton#338.29,21.60,70.0. Examine the river plain to determine if any river terraces are present. Describe any terraces you observe and how they are likely to have formed, or suggest an explanation for why there are no terraces present.                                                                                3 marks

3. Locate Horseshoe Bend (near Page, Arizona) by double-clicking its placemark. This feature is part of the Colorado River east of the Grand Canyon.

• Explore this part of the Colorado River by zooming out in Google Earth. Describe the type of river present. How is this river similar or different to the portion of Snake River you observed in Questions 1 and 2?                                                                                                                        2 marks
• Examine Horseshoe Bend in more detail by zooming in and using some additional perspectives. What type of river feature is Horseshoe Bend itself? How is it similar or different to Oxbow Bend in terms of erosional and depositional processes?                                                                          2 marks
• Open the Horseshoe Bend panorama by following the same procedure as before. It can also be viewed online at http://www.gigapan.org/gigapans/33145 and an alternative view is available at http://www.panoramas.dk/US/Grand-Canyon-horseshoebend.html. Observe the morphology (overall shape) of Colorado River as seen in the pans, and get a broader view by using the terrain perspective in Google Earth. Examine the river plain to determine if any river terraces are present. Describe any terraces you observe and how they are likely to have formed, or suggest an explanation for why there are no terraces present. You can get a broader view of the Colorado Plateau in this region using these links: http://www.airpano.com/360Degree-VirtualTour.php?3D=Horseshoe-Bend-Arizona-USA and http://www.airpano.ru/files/Goosenecks-Utah-USA/2-2.                  3 marks
• What do the differences in the morphology of the Snake River and Colorado River plains suggest about the tectonic history of these areas? Use your answers to questions 2b and 3c to help you.                                                                                                                                                               3 marks
• Find some evidence of an ephemeral stream in the vicinity of Horseshoe bend and include a labelled snapshot of it.                                                                                                      1 mark