Activity 32 “Modeling Erosion” Challenge . . . How do ocean waves affect the shape of the land?

Getting Started So far we have been modeling the kind of erosion made by water flowing down a hill or in a stream/river. Today you will investigate the earth processes at the coast of an ocean or a large lake. Share your ideas about erosion at the shore of a large body of water.

Key Ideas: Cliff erosion caused by waves begins with undercutting of the cliff below the water line. Depending on topography, this can lead to the formation of caves, arches and sea stacks The most common structures used to reduce the rate of cliff erosion caused by waves are: Sea walls made of concrete Large piles of boulders called riprap

Three basic types of erosion-control structures: Breakwaters (parallel to shore) Seawalls or ripraps (Parallel to shore) Jetty (perpendicular to shore) JETTY SEAWALL BREAKWATER RIPRAP

Procedure: Part A “Modeling Cliff Erosion” Read the procedure for “Part A” on pages 40-41. Be careful on step #5. Make sure you SLOWLY lift the wall STRAIGHT UP out of the box. For steps #7 and #8 you should create 20 total waves. You must record your observations in your journal after every 5 waves. This means you will have 4 observations before you begin step #9. IMPORTANT: Try to avoid splashing the sand and the water out of the box when you create the waves.

Procedure: Part B “Preventing Cliff Erosion” Read the procedure for “Part B” on pages 41-42. Make sure you add a bit more sand to the mixture when you complete step #11. You want the consistency (i.e., the “wetness”) of the sand to be the same as it was when you began Part A. Follow steps#4-9 in Part A for step #13. Step #14 will be completed as a group at your table before we have a class discussion. Make sure you record your conclusions when you COMPARE (i.e., find similarities) AND CONTRAST (i.e., find differences) the investigation with and without the retaining wall. IMPORTANT: Try to avoid splashing the sand and the water out of the box when you create the waves.

Procedure: Part C “Modeling and Slowing Down Beach Erosion” Read the procedure for “Part C” on page 42. The materials you are allowed to use in your construction . . . Long rectangular block Retaining rocks Smaller solid pieces

Analysis Questions Answers Analysis Questions #1-7 on page 43. The answer to all questions should be written in your journal.

1. The waves made the sand from the cliff model erode. Erosion The process began with erosion below the water Collapse of the cliff Deposition The material washed away was deposited on the bottom of the model.

#2 If the retaining rocks were placed directly against the cliff, you probably observed significantly less erosion. If the retaining rocks were placed a short distance away from the cliff, you likely observed a slowing of the process of erosion.

#3 A beach or underwater shelf was created at the bottom of the model cliff. The formation of the landform involved deposition of the sediments eroded from the cliff.

#4 Granite on a mountaintop will erode due to water flowing downhill. Granite on a cliff will erode from flowing water and wave action. Since the ocean’s waves are so powerful, it is likely that the cliff will erode more rapidly if the earth material is granite in both cases.

#5 There are two factors to consider regarding erosion: type of earth material and force of the eroding agent. Based upon earth material, Green Hill seems more likely to erode. However, based upon force of the eroding agent – waves vs. rain - Seaside Cliff seems more likely to erode.

#6 All of the structures slowed the erosion of a shoreline by breaking the waves before they hit the shore. The structures causes the waves to hit the beach or cliff with less force.

#7 The advantage of a wave-break structure is that it successfully shields the shoreline behind the structure from being eroded. However, a disadvantage is that the shoreline area to either side of the barriers experiences significant erosion. (The erosion is displaced, more than prevented.) Also, the cost of building such structures is high.