Using Google Earth to Investigate Streams

    Using Google Earth to Investigate Streams Objectives • Identify features of drainage basins, including channel evolution • Investigate and classify different types of stream drainage basin patterns • Collect and interpret data to calculate the gradient of different streams Laboratory Materials • Computer with internet access and GoogleEarth • Appendix F Pre-lab Assignment Prior to lab, read Chapter 13 Sections 13.2, 13.3 and 13.4 in your textbook. If GoogleEarth is not already installed on your computer, you will need to follow Step 1 in the exercise below to install this free program. Exercise 1: Streams are the number one agent of erosion on land, removing more sediment than glaciers, wind or ocean waves. The sediment eroded by streams is carried in the stream channel until it is deposited in a basin or flood plain. A drainage basin is the entire area of land drained by one stream or an entire stream drainage system made of a main stream and its tributaries. Common drainage patterns include: Dendritic Drainage Basin – resembles a branching tree in map view. The water starts high in the tributaries and flows into the main channel as the water moves downhill. This drainage basin pattern is found when water cuts through flat-lying layers of rock or sediment. It also develops where streams cut into homogenous rock, such as igneous rock or sediment. Rectangular Drainage Basin – a network of stream channels with right-angle bends that form a pattern of interconnected rectangles and squares. This pattern is associated with fractured or faulted bedrock. The water in the stream erodes the fractured and faulted bedrock. Radial Drainage Basin – channels flow outward from a central point and resembles spokes on a wheel. This pattern develops on conical, tectonically active hills, like volcanoes and structural domes. Centripetal Drainage Basin – channels flow inward towards a central point, often forming a lake or playa at the center of a closed basin because the water cannot flow outwards. This pattern is associated with structural basins. Trellis Drainage Basin – pattern resembling a vine on a trellis, where the main channels are long and run parallel to each other. The tributaries are short and flow at nearly right angles into the main channels. This pattern forms over bedrock that is made of alternating layers of resistant and nonresistant rock that have been tilted and eroded to form a series of parallel ridges and valleys. The main channels flow in the valleys and the tributaries flow down the ridges. In this exercise, you will be using Google Earth to investigate and identify different stream drainage basins in the U.S. Before you begin, please open Google Earth on your computer and the necessary Google Earth files. This program is free. 1. Step 1: Install Google Earth. Go to http://earth.google.com/intl/en/download-earth.html to download Google Earth to your computer. This program is free. If you already have Google Earth installed on your computer, go to the site to make sure you have the most recent version of the program. Follow the instructions to download Google Earth to your computer. 2. Type “38.18N, 100.42 W” in the “Fly To” search box. Google Earth with zoom into the location to the point that you can see trees on the ground. This is too close to answer the questions! Make sure you zoom out to an Eye Altitude of 18 kilometers. You can check the zoom height in the bottom right-hand corner of the screen. a. This area is an agricultural area developed near a stream. The stream is darker green than the surrounding farms. What type of stream drainage basin is found at this location?   b. Without any other information, what can you say about the bedrock in this part of Kansas? NOTE: Use your knowledge, not what you find in a Google search.   3. Type “41.41N, 122.20, W” in the “Fly To” search box and zoom to an Eye Alt of 32.6 km. The white you see is an area covered with snow. a. What type of stream drainage basin is found at this location?   b. Why is this drainage basin found at this location? What does it tell us about Mount Shasta?       4. Type “38.95N, 116.63 W” in the “Fly To” search box and zoom to an Eye Alt of 132 km. a. What type of stream drainage basin is found at this location?   b. Why is this drainage basin found at this location? What does it tell us about the underlying geology of this area? It may help to zoom out to view the entire state of Nevada with this one.     5. Type “35.14N, 119.68 W” in the “Fly To” search box and zoom to an Eye Alt of 3 km. a. What type of stream drainage basin is found at this location?   b. Why is this drainage basin found at this location? What does it tell us about the underlying geology of this area?   c. What major tectonic feature is found in this area? It may help to zoom out to answer this question.   6. What type of drainage basin pattern would you expect to find in the Appalachian Mountains? Explain why you would expect to find this pattern in that location.     a. Now, its time to test your hypothesis. Go to the Appalachian Mountains. West Virginia is a good place to look. What type of basin pattern do you see?   b. Sketch and label the drainage pattern you see in the Appalachians in the space below.     Exercise 2: Three processes are at work in all streams – weathering, transportation and deposition. Weathering dominates where the gradient or slope of the land is high and the stream physically erodes or cuts its channel into the bedrock. Transportation is the movement of eroded sediment downstream. Deposition of the sediment occurs when the stream velocity decreases and can no longer carry or push the sediment downslope. Because a stream changes from the point of origin or head down to their terminus or mouth of the stream, the stream’s channel changes as well. These changes are determined by the following factors: Geology – the bedrock geology of the land affects the streams ability to erode the channel. Gradient – this is the steepness of the slope at a point along the stream. Gradient is expressed in feet per mile and is determined by dividing the vertical change in elevation between two points on the stream (measured in feet) by the horizontal distance between the points (measured in miles). In general a stream’s gradient decreases from the head to the mouth of the stream. Base Level – this is the lowest point to which a stream can erode. As this point, the erosional power of the stream is zero and only deposition can occur. Discharge – the rate of stream flow at a given point on the stream at a given time. Discharge is measured in cubic feet per second (ft3/sec) and increases as you move from a stream’s head to its mouth. Load – this is the amount of material transported by the stream. Load plays a role in the depositional features that develop in a stream channel. Up near a stream’s head, the stream’s channel is fairly straight or slightly sinuous. The channel is narrow and the valley is V-shaped in cross-section. At this point in the stream, erosion dominates because the gradient is high (very steep). There are very few, if any, depositional stream features present. As the stream moves downslope, the channel becomes more sinuous until it is classified as a meandering channel. Meandering channels have significant bends present. They form where the gradient is low and deposition dominates. Meandering channels occur within the stream’s floodplain, which is a flat area carved overtime by the channel. The area is filled with sediment deposited by the stream during floods. Erosion is highest on the outer bends of the meanders. Deposition occurs on the inside of the meanders. Point bars, made of sand, are deposited on the inside of the meanders. The stream channel migrates over time towards the outside edge of the meander. Other features found in association with meandering channels are oxbow lakes, natural levees and yazoo tributaries. Braided channels are unique channels found in flat-bottomed valleys where the stream flow is variable. These channels have a high sediment load and variable discharge, which results in a pattern of multiple channels separated by sediment bars. Braided streams are associated with glaciers, as the melt varies through the day and the year. Braided streambeds can also be found in deserts and other places with wet and dry seasons. In this exercise, you will practice identifying different channel shapes found along streams. Type “Ennis, Montana” into the “Fly To” window. You will be taken to the location shown in Figure 1 of Appendix F. Once there, you will be able to zoom in and out of the various locations to answer the questions about the stream channel types found in this one location. 7. Zoom into Area A. a. What channel shape is found in this area? (Select one): _____straight _____sinuous _____meandering _____braided b. Why does this area have that channel shape?   8. Zoom into Area B. a. What channel shape is found in this area? (Select one): _____straight _____sinuous _____meandering _____braided b. Why does this area have that channel shape?   9. Zoom into Area C. a. What channel shape is found in this area? (Select one): _____straight _____sinuous _____meandering _____braided b. Why does this area have that channel shape?   10. In which area would you expect to find the highest gradient? _____Area A _____Area B _____Area C 11. In which area would you expect to find the highest sediment load? _____Area A _____Area B _____Area C 12. In which area would you expect to find the lowest gradient? _____Area A _____Area B _____Area C 13. Now, you will calculate the gradient of each of the three areas. To calculate gradient, you will need to zoom in and measure the elevation (shown at the bottom section of the Google map screen) and horizontal distance (use the Google Earth ruler) between two places in Google Earth along the streams. Make sure your measurements are taken on top of the river channel. Then, you can calculate the gradient with the data you collect. Location Point 1 Elevation (feet) Point 2 Elevation (feet) Elevation Difference between Pt 1 and 2 (feet) Horizontal Distance between Pt 1 and 2 (miles) Calculated Gradient (feet per mile) Example 487 ft 379 ft 108 ft 3.69 mi =108ft/3.69mi = 29.27 ft/mi A B C 14. How did your answers in question 13 compare with your hypotheses in questions 10 and 12?     15. What general statement can you make about gradient and channel shape?       16. Type “33.32N, 93.69W” into the “Fly To” window and zoom in to an Eye Alt of 13 km. You will be looking at a segment of the Mississippi River. What channel shape is found at this location?         17. What depositional and erosional features do you see at this location? List all the features: Erosional Features Depositional Features 18. Type “Lake Wisconsin” into the “Fly To” window and zoom in to an Eye Alt of 8 km. Check the northeastern area of the lake, what is happening to the sediments as the river enter the lake?     19. Type “Liberty, WI” into the “Fly To” window and zoom in to an Eye Alt of 35 km. What drainage pattern is found at this location?