FOCUS: Our study of the geosphere begins with a look at how, over time, the powerful agents of erosion have shaped and formed our landscape. Gravity, water, wind, and ice are constantly weathering, wearing away, and moving rocks, soil, sand, and sediments and depositing them elsewhere. We’ll also consider the impact humans have on erosion, deposition, and our ever-changing landscape.
Objective: To begin to explore and ask questions about erosion.
Find a good example of erosion on the school grounds for children to visit, and ask children what they think is going on.
DROP BY DROP
Objective: To use a model to investigate the effects of water drops falling on bare soil.
Ask the children if they think that a drop of water could be an agent of erosion – could it move soil, sand, or fine sediment around? How could we find out?
One way would be to drip water on some soil to see if it causes a change. Place a mound of dry soil on the sidewalk or pavement. Have a child measure and record the height and width of the mound. Now have children take turns using a baby bottle or dropper filled with water to squeeze one drop at a time onto the mound, noting what happens as it strikes the dry soil. Compare the effect when water drops hit the center or edges of the mound. Test if there is a different effect if you raise or lower the height of the dropper. Does the height from which the water falls affect how far the soil is splashed?
Switch to a spray bottle and continue to “rain” onto the mound. What happens as more and more water rains down? (It forms puddles, streamlets.) Finally, measure the height and width of the mound again. How is it different? (Shorter and more spread out.) Can raindrops move soil?
Materials: for each small group: eyedropper and/or baby bottle, spray bottle, water, dry soil supply, tablespoon measure, ruler.
SHAKE IT UP
Objective: To use a model to investigate the erosion of rocks carried by moving water.
How could we model what happens to rocks when they are carried by a fast-moving river, or picked up by waves and thrown against the shore? One way would be to put some rocks in a jar of water and shake them up. Place ten pre-washed rocks (approximately walnut-sized works well) into each of two plastic containers with screw-on lids. One jar will be shaken, and the other jar will be set aside and not shaken, to serve as a control. Measure and add one cup of water to each jar, and screw on the tops securely. Ask the children for their ideas about what might happen, if anything, to the rocks being shaken together.
Set the control jar to one side, and pass the other container from child to child, with each person giving it ten to twenty shakes, so that the jar gets at least 100 shakes. Now compare the two jars. How clear is the water in the jar that was shaken, compared to the control?
Using two kitchen strainers lined with coffee filters, pour the water from each jar through a filter into a clean, labeled jar. Note and describe any material collected on the filters. Which sample had more sediment? Which sample had the cloudier water? Is there any noticeable difference in the rocks? Where did the sediment come from? (Chipped off the rocks as they bumped together.) Where in nature might this kind of erosion be happening? (In fast-moving streams, waterfalls, waves on the sea shore.)
Materials: Two sets of ten similar-sized rocks, rinsed to remove sand; two plastic pint-sized containers with screw-on lids, cup measure, water, two kitchen strainers, paper coffee filters, two clear pint-sized containers, one marked “shaken” and one marked “control.”
Objective: To use a model to study the effect of wind erosion on loose sediments.
Wind picks up loose sediment, like sand and dust, and moves it around. What factors might affect how and where sediment is deposited?
Wind-shaping: Beforehand, prepare aluminum baking trays by poking three holes, evenly spaced, along the longest side of the pan, at mid-level height (or you can use clear lettuce boxes with lids, making a single hole in one side). Spread sand at least one inch deep throughout the tray, leaving some space along the side with the holes. Bury small objects in the sand and include a few small rocks for barriers. Secure the snap-on lid in place. Have the children take turns using balloon pumps to blow at the sand from different angles (across the top, at the base, from the side) to simulate blowing wind. Observe what happens to the sand, depending on wind direction or force. Do they notice any patterns? How does varying the force affect how far the sand moves? What effect does varying the angle have? Look for wind shadows, places protected from the wind where sediments build up. Where in nature might this kind of erosion be happening? (Beaches, deserts, places where the soil is exposed.)
Optional: try using a turkey baster, empty condiment spray bottle, or other blower to move the grains. How does strength of the wind affect the results?
Wind-sorting: Place a large lasagna or roasting pan on the ground. Mark three crosswise lines, dividing the pan into four sections. Make a mixture of different sized pebbles ranging from ¼” to 1” in diameter (about one cup total). Pour this mixture out in a row, about two inches from one end of the pan. Now have the children take turns using the balloon pump to blow on the pile from this end of the pan so it spreads out lengthwise. After a few pumps, analyze which materials ended up in each section. Was there a difference between how far the smallest, lightest kinds traveled and how far the heavier kinds traveled? Where might sorting like this occur in nature? (Beaches, deserts.)
Alternative: Instead of using pans, put dry sand and obstacles like rocks on blacktop or sidewalk and use balloon pumps to see how it moves around.
Materials: aluminum baking trays with plastic snap-on lids or clear plastic lettuce boxes, balloon pump, dry sand, small items to hide such as coins, glass beads, shells, figurines, different sizes of seeds, a few small rocks; optional: turkey baster, condiment squirt bottle. For Wind-sorting: large lasagna or roasting pan, marker, about half a cup of each of sand and different sized pebbles ranging from ¼” to 1” in diameter.
UPPER GRADES CHALLENGE: Angle of Repose (Grades 5-6)
Objective: To use a model to measure and compare the angle of repose of a variety of different materials.
The angle of repose is the maximum angle that a granular material will take before it begins to slide, the maximum angle when this material is stable. How does the angle of repose of different materials compare?
Place a piece of letter-sized paper on a table, close to one edge. Carefully pour one cupful of dry rice onto the paper to make a pile. Hold a protractor up against the edge of the table so that the ‘0’ is lined up with the outer edge of the rice pile. Now, looking at the pile from the side, at eye level, move the protractor arm up or down until it is parallel with the slope of the rice pile. Read the angle. This is the angle of repose of rice. Try other granular materials to compare, such as cornmeal, split peas, kidney beans, dry sand, wet sand, pea stone, etc. How do the angles of different materials compare? How might this affect erosion on hillsides or excavation sites?
Where might the angle of repose determine how steep a slope is in nature? (Landslides, dunes, eroding cliffs, avalanches.)
Materials: for each small group: white paper, protractor (preferably with moveable arm), one cupful each of materials such as sand, pea stone, cornmeal, rice, lentils; Angle of Repose data sheet.
PUPPET SHOW “Just Wearing Away”
Objective: To meet some agents of erosion and learn how they move and shape the landscape.
Perform the puppet show, or have a group of children perform it for the class. Afterward, ask questions to review the key details and vocabulary in the story. What does “erosion” mean? (Wearing away and carrying away.) What were the different agents of erosion in the puppet show? (Glaciers, gravity, wind, rain, rivers, waves.) How does each of these agents cause erosion to happen?
Materials: puppets, script, props, stage.
Objective: To learn more about erosion and how to control it through pictures of real life examples.
Show pictures to illustrate the effects the various agents of erosion can have on the landscape and to show some new methods used to control erosion.
Materials: slides or pictures of erosion and control methods, projector, screen.
DESIGN CHALLENGE: HOLD THAT SOIL!
Objective: To design and build a system to prevent erosion and the loss of topsoil on a bare hillside.
Ahead of time, collect soil and use it to form sloping “hillsides” within plastic dish basins. Create one “hillside” basin for each small group of children and one additional to serve as a control. Pat the hillsides down a bit to hold the soil in place, with the bottom ending about three inches from the opposite side of the basin.
Gather the children in a circle around the control basin. Ask the children what they think will happen to the “hillside” if it rains? What will the water that collects in the basin look like? To simulate a rainstorm, pour a quart of water onto the hillside with a watering can and have the children observe and discuss the results.
Ask the children to use the knowledge gained from previous experiments and the pictures to design a system for preventing soil erosion on the basin “hillsides.” The main criterion for success is for the water that collects in the basin to be clear, not carrying any sediment off the hillside. The main constraint is to use natural materials available around the school grounds. In small groups, have children discuss their ideas and decide on a plan to implement. Then have them gather materials for construction. Have them draw or describe their design in their journals. Have the groups bring their basins to a central gathering place once they have built their erosion control system. One at time, have each group explain how they protected the soil on their hillside. Test each design by pouring a quart of water onto it. Discuss the results. What designs seemed to work well to slow runoff? What would they do differently if they could do this experiment again?
*Afterward, have children dismantle their structures and return materials they collected.
Materials: white plastic dish basins, one per team and one for a control; soil to form “hillsides” in each basin, journals or clipboards and paper, pencils; optional: additional natural materials such as twigs, dead leaves, bark, dried grasses and weeds, small stones.
Objective: To think about the many ways in which erosion is important in our lives.
Ask the children where the soil in which we plant our gardens comes from. What about sand on beaches or sand dunes? What about mountains where we like to hike or ski? What about lakes and rivers where we can go fishing or swimming? Have the children write about or draw a picture of one thing they like to do in a place that was made or changed by erosion. Afterward, in small groups, have them share their journal entries.
Materials: science journals or paper and clipboards, pencils; optional: colored pencils.
Objective: to review the different agents of erosion and how they wear away rocks and soil and change the landscape.
Have children complete this sentence: If I were an agent of erosion, I’d like to be _____________(gravity, rain, a river, a glacier, etc.) so I could ___________________.
A STEP BEYOND
Erosion in Action: Make a mound of soil two to three feet high at the edge of the schoolyard. Have students record its measurements (height, width, circumference). Place a rock or two near the top of the mound to represent Benny Boulder and Roger Rock from the puppet show. Discuss how the mound might change over time, and what factors (rain, wind, animals, children) might affect it. Observe changes, especially after precipitation, taking measurements at intervals to compare to the original dimensions.
Soil Splash: To measure how high soil can be lifted and splashed, use a watering can to “rain” on bare soil in the schoolyard. Wrap a four-sided half-gallon milk jug or juice carton in white paper, taped on securely, and label each side with the height from which the water will be poured (e.g. 6 inches, 1 foot, 2 feet, 3 feet). The paper on the milk jug will show how high soil gets splashed. Place the milk carton about six inches away from the patch of bare soil. Have children take turns sprinkling water, watching to see where the dirt splashes on the paper. Repeat at four different heights, turning the milk jug for each trial. Afterward, measure and compare the height of the soil marks on the paper. Does the height of the watering can affect how high the soil is splashed? Where in nature might this kind of erosion be happening? (Wherever rain falls on bare soil.)