River Erosion Gizmo Answer Key

Name: Nicolas Franco Date: 12-14-2022 Student Exploration: River Erosion Directions: Follow the instructions to go through the simulation. Respond to the questions and prompts in the orange boxes. Vocabulary: cutbank, discharge, erosion, flood, floodplain, meander, meandering river, oxbow lake, point bar, river speed, sediments, slope, streambank, streambed, tributary, weathering Prior Knowledge Questions (Do these BEFORE using the Gizmo.) 1. The image above shows a raging mountain river in full flood. What do you think is making the water brown in color? Dirt or sediment carried by the river. 2. What impact do you think the flooding river will have on the surrounding landscape? Roads would be moved, houses would be destroyed, riverbanks would be ruined, etc. Gizmo Warm-up If you stand by the bank of a river, it may seem that very little is happening. But over thousands and even millions of years, rivers can have a profound effect on the landscape. In the River Erosion Gizmo, you will see how rivers move materials and how they affect landscapes. To begin, check that Mountain stream and Short-term erosion are selected. The Gizmo shows a typical stream that is moving through a hilly area. 1. The two movie cameras ( ) allow you to observe different parts of the stream up close. Click on the left movie camera. What do you see? A rocky stream and little particles being transported. 2. Sediments are small rock fragments such as sand or pebbles. What evidence do you see that sediments are being transported? Sediments being moved from left to right. 3. Now select the right movie camera to see the bank of the mountain stream. What is happening to sediments on the bank? Sediments are falling into the stream. Get the Gizmo ready: Activity A: Mountain streams ● Check that Mountain stream and Short-term erosion are selected. ● If necessary, click outside the circle to close the zoomed-in view. Introduction: Erosion occurs when sediments and other materials are moved from one place to another. Along with weathering, which is the breakdown of large rocks into smaller sediments, erosion can have a profound impact on the landscape. Question: How does river erosion affect landscapes in the mountains? ✏️ 1. Label: First, get to know some of the different parts of a mountain stream. Turn on Show labels. Label the image to the right, then fill in the word that goes with each description. A small stream that flows into a larger stream: tributary A place along a stream where water drops straight down: waterfall A letter that describes the shape of a typical mountain valley: V-shaped valley The side of a stream: streambed The bottom of a stream: streambank 2. Observe: Turn off Show labels. Next to “Release barrel,” click Play ( moves as it floats down the stream. ). Observe how fast the barrel What happens when the barrel goes over the waterfall? It continues to be on the side that it was before it plunged from the waterfall. 3. Calculate: The two red flags are 100 meters apart. The time at which the barrel passes the flag is shown. Remember, there are 60 seconds in a minute. A. How many seconds did it take for the barrel to go 100 meters? B. To find the barrel’s speed, use a calculator to divide the distance traveled (100 m) by the time it took the barrel to float 100 m. The units are meters per second (m/s). What is the speed of the barrel? 1 min 30 sec 100m/90sec =1.1 4. Record: Click Reset ( ). Turn on Show data. A. The slope of the channel is how steep it is, or how many meters the streambed drops for every horizontal kilometer. What is the slope of the stream? The slope travels one kilometer in 22 minutes. The slope is steep and gets steeper as it descends. B. River speed is a measure of how fast water flows. What is the river speed? 1.1 meters per second C. How does the river speed compare to the speed of the barrel you calculated on the previous page? They are both identical in every way. D. Discharge is the water volume that flows past a given It is 2.3 meters cubed per point every second, measured in cubic meters per second. As the barrel moves second (m3/s). What is the stream’s discharge? down, the volume is calculated E. What types of sediments are transported by this stream? The more quickly sediments travel, the more rocks are scooped up from the stream. Sediments are classified by size. The smallest sediments are clay particles, followed by silt, sand, and pebbles. Larger sediments include cobbles and boulders. 5. Observe: Turn off Show data. Next to River flow, select Flood. Look at the landscape, and then click on the movie cameras to see zoomed-in views. Describe what you notice below. One perspective shows rocks falling from the waterfall, another camera can be showing the difference in color of the rocks in the stream. The color of the rock sediments can vary depending on the perspective of the camera. 6. Calculate: Click Play to release the barrel. How many seconds does it take the barrel to get from one flag to the other? What is the speed of the barrel? Time: 31 seconds Speed: 100m/31s=3.2m/s 7. Compare: Turn on Show data. During a flood, how do the river speed, discharge, and transported sediments compare to normal flow conditions? A flooded river moves significantly more quickly than an ordinary river. The value of the discharge river is different from that of a normal or flooded river. Get the Gizmo ready: Activity B: Meandering rivers ● Select Meandering river. ● Select Short-term erosion, Low vegetation, and Normal river flow. Turn off Show data. Introduction: Meandering rivers are found in flatter areas. Unlike the V-shaped mountain valleys, the valleys of meandering rivers have wide, flat bottoms called floodplains. Question: How does river erosion affect landscapes in hilly or flat areas? ✏️ 1. Label: Turn on Show labels. Label the image to the right, then fill in the word that goes with each description. A large S-shaped bend in a river: Meander A flat area next to the river Floodplant A steep stream bank on the outside of a bend in the river: Cutbank A gently sloping deposit of sediments on the inside of a bend in the river: Point bar 2. Observe: Turn off Show labels. Click Play to release the barrel. Observe the path of the barrel as it floats down the river. (The flags are 100 meters apart.) A. How many seconds did it take for the barrel to go 100 meters? (Remember, there are 60 seconds in a minute.) 125 sec B. What is the speed of the barrel? 0.8 m/s C. Turn on Show path. Did the barrel stay in the center of the It went from side to side river or go from side to side? D. As the barrel went around each meander, did it stay closer to the point bars or the cutbanks? Cut banks In a meandering river, the water flows faster on the outside of a meander, near the cutbank, and moves more slowly near the point bar on the inside of the meander. The current carries the barrel toward the cutbanks and away from the point bars. 3. Compare: Click Reset. Turn on Show data. List the slope, speed, discharge, and transported sediments of the meandering river. Then select Mountain stream and fill in the remainder of the table. Change back to the Meandering river and compare the values. Slope Meandering river 1.0 m/s Mountain stream 22.0 m/s Speed 0.8 m/s 1.1 m/s Silt and Clay Sand, Silt, and Clay Discharge Transported sediments In what ways is a meandering river different from a mountain stream? The slope and speed of a mountain stream are greater than those of a meandering river, but the discharge is smaller. 4. Observe: Turn off Show data. Click the right movie camera to see the cutbank. Look at the sediments just above the water. What do you see? Particles falling Now select the left movie camera to see the point bar. Look at the sediments in the water. What do you notice? The point bar has fewer sediments than the cut bank. Erosion occurs at the cutbank, where water is moving faster. As a result, cutbanks are steep and often overhanging. Sediments are deposited in the slow-moving water near point bars. 5. Compare: Click in the simulation area to turn off the movie camera. Select Flood. A. The flat area surrounding the river is called a floodplain. Why do you think it has this name? It is a big area/plain flooded with water B. Why might it be a bad idea to build a house in a floodplain? Due to the destruction of the natural environment and the rarity of various species' habitats due to construction on floodplains, there is a high chance of flooding in your home. C. Turn on Show data. How do flood conditions differ from normal conditions? During a flood, the river's speed and discharge are increased. D. Look at the two close-up views. What do you notice? I noticed that the sediments nearthe point bar are no longer going to the ground of the river Activity C: Long-term erosion Get the Gizmo ready: ● Select Mountain stream. ● Select Long-term erosion and Low vegetation. Introduction: Both in the mountains and in flatter areas, river erosion can cause large changes to the landscape over time. In this activity, you will observe some of these changes. Question: How do rivers change landscapes over long periods of time? 1. Predict: How do you think the mountain valley will change over time? Mountain ranges will begin to crumble, and vegetation will begin to disappear. 2. Observe: Click Play. Observe the valley for 200,000 simulated years. What do you notice? The mountain's elevation dropped, 3. Analyze: Click Reset. Turn on Show data. Record the slope, speed, and discharge of the stream. Click Play, wait until the end of the simulation, and record the same data. Year 0 200,000 Channel slope 22 14 River speed 1.1 .8 Discharge 2.3 2.8 How does the stream data change over time? River speed and canal slope gradually decline as discharge gradually rises. 4. Observe: Click Reset. Click the movie camera to see a side view of the valley. Click Play. Over time, does the valley erode downward or side to side? The valley erodes downwards 5. Compare: Click Reset. Next to Vegetation, select High. Click Play. Compare the end result of 200,000 years of erosion with high vegetation to erosion with low vegetation. Which landscape eroded more, and why do you think this is so? The first land 6. Predict: Click Reset. Select Meandering river and Low vegetation. How do you think the meandering river valley will change over time? The river will grow and possibly become wider. As the river takes over, the land will also begin to lose some of its features. 7. Observe: Click Play. Observe the valley for 2,000 simulated years. (The time frame is much shorter for the meandering river valley because changes occur faster there.) A. What do you notice? It spread out more and is no longer compact B. Over time, do the meanders grow wider or narrower? The meanders grow wider C. How does the width of the floodplain change over time? It get more narrow the more it separates the river D. Turn on Show labels. What feature is formed when the river breaks through the narrowest part of the meander? An oxbow lake E. Click Reset. Turn on Show data. Click Play and observe the river data. It goes 1m per kilometer, and the river discharge get greater How does the river data change over time? 8. Observe: Click Reset. Click the movie camera to see a side view of the valley. A. What do you notice about the shape of the river channel? The river's waterway has a shore and a curved shape. The river shifts to the left as it erodes more. B. Click Play. Does the channel erode downward or side to side? Side to side Meandering rivers cause little downward erosion. Instead, the channel moves sideways as sediments are eroded from the cutbank and deposited on the point bar. 9. Compare: Click Reset. Next to Vegetation, select High. Click Play. Compare the end result of 2,000 years of erosion with high vegetation to erosion with low vegetation. Which landscape eroded more, and why do you think this is so? More erosion occurs in areas with less vegetation than in areas with no vegetation. Deforestation is a factor in soil erosion. Water will remain longer if there is more vegetation.