Analyzing Rivers with Google Earth

Transcription

1 Name Per. Analyzing Rivers with Google Earth River systems exist all over the planet. You are going to examine several rivers and landforms created by rivers during this activity using Google Earth. While your ipad can view each location, you will need a laptop to use the ruler function. A B Figure 1: Meandering river terms. Image from: Part I: Meandering Rivers: Figure 1 shows several terms used to describe meandering rivers. We are going to focus on wavelength, amplitude, and sinuosity. Sinuosity is the ratio of river length (distance traveled if you floated down the river) divided by straight length line (bird s flight distance, i.e. from point A to B). The greater the number, the more tortuous (strongly meandering) the path the river takes. 1. Fly to Yakeshi, China. Just north of the city is a beautiful series of scroll bars (former point bars that have been abandoned) formed by the meandering river moving across the landscape. 1a. Describe the features you see. What age river is this (young, mature, old)? How are the meanders moving over time? Is the river becoming straighter or more curved?

2 1b. Find an area where the current river channel and clear meanders are easy to see (i.e. 49 o N, 120 o E). Measure the wavelength, amplitude and sinuosity of the river in this area. To measure straight line paths for wavelength, amplitude, and bird s flight distance, go to Tools Ruler Line. Use kilometers. Click and drag your cursor across the area of interest. Wavelength = km Amplitude = km To measure sinuosity, first draw a transect across the area you want to measure using the Line function in the tools menu. Write this number down in the denominator in the equation below. Leave the transect line there. To measure the path along the river, go to Tools Ruler Path. Click at the beginning of your transect line, and then click repeatedly along the path of the river until you get to your ending place on your transect line. Sinuosity = Path along river = = Bird s Flight Dist. 2. Fly to Black Diamond, WA. Move south and a little west of the town to so that you are centered over a large meander bend in a forest. This is the Green River. There should be a little button labeled 1990 or 1998 in the lower left of the screen. Click on that. You ll notice that the image changes back to 1990 and a tool bar with dates shows up in the upper left of your screen. If you don t see it, make sure Historical Imagery is turned on in the View menu. 2a. Describe how the river has moved over time and any changes in features you see. 2b. Zoom in on the meander curve located at 47 o N and 122 o W. Measure how far this meander curve has moved between 1990 and Do this by measuring the sinuosity for both 2013 and Do 2013 first and then leave the drawn transect and path lines there when you change to The movement of the river will be very obvious Sinuosity = Path along river = = Bird s Flight Dist Sinuosity = Path along river = = Bird s Flight Dist. Has the meander become more or less extreme with time? Is this what you would expect? Why or why not?

3 3. Fly to Harbin, China and then move a bit west on the image so that you see several clear meanders near Xu Wanzhentun. This river isn t too far away from Yakeshi and also has scroll bars. 3a. Measure the wavelength, amplitude, and sinuosity for meanders in this area. Wavelength = Amplitude = Sinuosity = 3b. Have the meanders become more or less extreme over time(based on what you can tell from the scroll bars as there are no historic images for China)? Is this what you would expect? Why or why not? 4. Fly to Carauari, Brazil. 4a. List at least 4 features of the river and state whether this river is young, mature, or old. 4b. Do you think the town is at risk for flooding? Why or why not? 5. Fly to Riberalta Bolivia. Zoom out and note that there are two rivers: the large one next to the town, and a much smaller one further to the north. Compare the features you see at these two very different-sized rivers. Do you think the scale of the river has an effect on the types of features that rivers will develop? Why or why not? Part II: Entrenched Meanders: 6. Now you re going to look at meandering rivers in bedrock. Fly to Supai, AZ. Zoom out and go a little to the NW, and find a meandering section of the Grand Canyon. 6a. Measure sinuosity, amplitude, wavelength over ~9 km (straight line) of the river. Wavelength = Amplitude = Sinuosity =

4 6b. Zoom into the bottom of the canyon and follow the river through a few meanders. Note that while the river strongly meanders, there are few, if any, point bars. Why do you think this is? 6c. Meandering is a sign of an old river, and meanders usually form on flat low-lying flood plains where the gradient is low. Steep canyons, on the other hand, are a sign of a young river. A river that has steep canyons and meanders is called an entrenched river. How did the Grand Canyon form such deeply incised meanders? 6d. To see how extreme some of the meanders are in some of the entrenched rivers in this area, fly to nearby Gooseneck State Park, UT. Measure the sinuosity in the extreme meanders just to the northwest of the park. Sinuosity = 6e. Fly to nearby Lake Powell, UT. Lakes are usually rounded in shape with smooth shorelines. Why is Lake Powell so strangely shaped? How was it formed? 7. Fly to Wutai, Taiwan. You should be looking down at a mountainous landscape with some seriously meandering rivers. Zoom in and fly around the landscape. 7a. Contrast this entrenched river to the Grand Canyon. What features do you see at the base of this river valley that is lacking at the Grand Canyon? 7b. Note that in the narrow river valleys there are areas where the stream is braided. What does this say about the sediment load and velocity of the rivers in these valleys? 8. There are also entrenched rivers in Washington State. Fly to Pomona, WA. Zoom out and fly north and a little east to the Yakima River Canyon. The Yakima River cuts through Columbia River Basalt flows in this area. What is the difference in topography on the inside verses the outside of the meander curves?

5 Part III: Tree-Shaped River Features: 9. Fly to Kimberly, Australia. Zoom in and fly northwest to ~17 o 11 S, 125 o 54 E. You will see a river system that looks like tree branches. 9a. What is this part of the river called? 9b. Where the branches all join into one river, which direction does this river flow? 9c. Measure distance from farthest branch of the easternmost area to the main trunk: We will use this number for comparison to another area later. 10. Fly to the Lena delta, Russia. 10a. What type of rivers do you see in this area and what does this indicate about the amount of sediment being transported and the energy of the water in this area? 10b. The Lena Delta is one of the a few deltas located in the arctic. The land in this area is considered tundra and is dominated by permafrost. Zoom in and note the unusual circular and oval patterns in the delta. Go to and read about this unusual delta. What does the author say causes the complex patterned ground on the delta plain? Part IV: Large-scale River Features: 11. Fly to Markle Pass, MT, and move to an area where there are east-west trending ridges around 47 o N, and 114 o W. 11a. What are the ridges and how did they form? (Hint: you saw these in a video during class). 11b. Fly to Astoria Canyon, which is off the coast of Oregon near the town of Astoria. This canyon was formed at the same time as the ridges near Markle Pass. How was this canyon formed? Why is the beginning of the canyon about 20 kilometers from the mouth of the Columbia River?

6 12. Fly to Khabary, Altayskiy kray, Russia. Zoom out and move a little west until you see north-south trending low ridges. 12a. What is the latitude of this area? 12b. These ridges are similar to the ridges you saw near Markle Pass, MT. What does this say about the geologic history of this area? Is this reasonable for the latitude of this area? 13. The features you looked at in questions 11 and 12 are much larger than normal river features. Once again, the idea of scale is important. Do features of rivers change when either going to very small scales (as in question 5) or to very large scales? Why do you think this is the case? Part V: Mars: Now you will compare the river features you have examined on Earth to some features on Mars. Click on the button that looks like Saturn and select Mars. 14. Go to Shalbatana Vallis. Zoom way out and look to the east around 7 o 40 N and 45 o 18 W. 14a. What is this feature? 14b. Use the ruler tool and measure the wavelength of this feature. How does it compare in size and appearance to similar features you have viewed on earth? 15. Fly to Tiu Valles and look at the teardrop features to west of location. The teardrop features are scour features. The point of the teardrop indicates the direction of flow. If these features were carved by an ancient river on Mars, which way did the river once flow? 16. Fly to Thaumasia Fossae. Zoom way out, and go north to 42 o S and 93 o W. 16a. Which location on earth that you visited does this resemble the most? 16b. If this feature was created by an ancient river, which way did it flow? 16c. Use the ruler to measure the distance from the edge of one branch to the place where all the branches meet: How does this compare to the scale of what you measured in the similar place on Earth? 17. In general, what does the scale of these possibly river-carved features on Mars say about the volume of fluid that may have once flowed on its surface? (Note that there is still some debate about how these features were created, and what, if any, fluid created the features).