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TOPIC-TITLE Physical Parameters - Erosion Creates a Change in the Landscape AUTHOR Guy Jacob GRADE SUITABILITY Middle School SCOPE Earth Science

Sequence Before introducing the topic of erosion, you should teach students about waves. What is a wave? What can it do to the landscape? After students discuss erosion, lead them through a discussion on controlling and reducing erosion. < < go top

Background Summary The ocean is constantly in motion. Currents, tides, and waves that move ocean waters are the result of the Earth's position in the solar system, the rotation of the Earth, and actions that occur between the Earth and its inhabitants. Waves are generally produced by wind. The wind moves over the surface of the water, causing the water to rise. The stronger the wind, the higher the water rises, producing larger waves. When the wind is steady, it produces a wave train, which is a series of consecutive waves. As waves approach the shore, they move over shallow water. When the bottom of the wave hits the seafloor, the top of the wave moves forward and crashes. This process forms a breaker. When the incoming tide reaches the mouth of a river, another type of wave is formed. If the seafloor slopes at the mouth of the river and the tidal range at that point is more than five meters, a wave known as a tidal bore would be created (Greene, 1998). Sudden changes in the Earth's crust can lead to another type of wave, referred to as a tsunami. According to Greene (1998), an earthquake on the seafloor created a turnami off Japan in 1993. Currents, tides, and waves move not only the water in the ocean but also move sediments along the shoreline. The movement of these sediments is called erosion. When the sediments are relocated along a beach, it is termed deposition. When a wave crashes against a beach, sand is suspended into the water and may drift with the current. During storms, waves and currents have more energy; therefore, more sand may be removed. Governmental agencies attempt to contend with the problem of coastal erosion in a number of ways. One way is to create a barrier. A groin is a rock or wood barrier that extends from the beach into the water. A jetty is another type of barrier. Jetties are designed to trap sand drifting along the shore with the current, to prevent sand accumulations in a channel. When a large quantity of sand has eroded from a beach, one way it can be replaced is to pump the sand in the water column back to the beach. This process is known as dredging. All of these processes are temporary methods to reduce or control erosion. Researchers are currently testing a new erosion control theory. This new type of erosion control is a submerged artificial reef. According to Greene (1998), large concrete blocks that interlock are placed approximately 100 meters offshore. As the waves move toward the shore, they reach these concrete blocks and break. The sand then increases between the artificial reef and the shore, preventing the shore from eroding. This process may also be only a temporary solution as the sand beneath the reef eventually erodes, compromising the reef. Further studies must be conducted to determine whether this is the best and most natural course of action. < < go top Objectives Students will be able to conduct experiments to show evidence of soil erosion. < < go top Materials 20 rulers (4 for each group) All-purpose sand (70 lb. bag) Pencils Tap water Paper 5 rectangular pans or plastic bins (at least 9" or 12") < < go top Activity Divide students into five cooperative learning groups. Provide each group with a pan, sand, water, four rulers, paper, and pencils. Have students place sand in their pan approximately 1 2" thick on one half of the pan. Gently add tap water up to 2" deep on the side of the pan. Label the shorter sides of the rectangular pan, east and west. Have student groups draw a diagram of their respective pans. One student in each group should take a ruler and create a "wave" action against the shore in a general east-to-west movement. Ask the students to make a drawing after creating the wave action--noting the effects of erosion. How has the coastline changed? Following Step 7, have students place two or three rulers into the sand about 4" apart to represent groins. Have them develop a hypothesis for the function of groins. Draw these groins and shoreline. Use a ruler to create the same east-to-west wave movement. What happened in between the groins? What happened to the shoreline? What happened to the west of the last groin? Make a drawing after the wave action is complete. < < go top Possible Extension Obtain a slide of beach groins. Demonstrate beach groins to the class and discuss their thoughts. Compare and contrast jetties with groins. Groins protect barrier beaches. Both jetties and groins can be constructed of rock; however, jetties tend to be longer and protect channel or inlet areas. Humans can modify the landscape as does mother nature. How would you feel if you could not access a beach? Would you want tax dollars spent to have the effects of erosion controlled by human technology? < < go top Teacher Evaluation Have student groups write possible reasons the sand was eroded to the west of the last groin. Also, have student groups write how the problem could have been prevented. Students may wish to draw a plan demonstrating how shoreline erosion should have been prevented. < < go top