DAY ONE – INTRODUCTORY ACTIVITY
1. Have students log on to the interactive game “Shape It Up!” Explain that this game will challenge them to identify the forces that shape the earth’s surface and the relative speed with which they act. After explaining that “erosion” is generally a process whereby the earth’s surface is worn down, provide students with a FOCUS FOR MEDIA INTERACTION by asking them to determine which of the game’s four earth-shaping forces (wind, water, glacial and volcanic activity) is NOT a force of erosion. Allow students to play the game for approximately 5 minutes-enough time for everyone to have played every scenario in the game.
2. Review the focus question by asking which of the four earth-shaping forces in the game is NOT a force of erosion. (If students don’t answer “volcanoes,” explain that while erosion is generally a process whereby the earth’s surface is worn down, volcanic activity generally raises up the earth’s surface.) Have students click on the “Learn More” button and ask for four volunteers to each read one of the paragraphs describing the geological process in the game. Explain that water, wind, and glaciers are all forces of erosion. Erosion describes the process by which small particles of rock (or sediment) are washed, blown, or scraped away, wearing down the surface of the earth.
3. Explain that large rocks first need to be broken down into smaller pieces in order to be worn away by erosion, and that this is accomplished by weathering-the breaking down of rock by chemical or mechanical processes. Explain that the remainder of this lesson will explore and explain the phenomenon of weathering and erosion in greater detail, beginning with weathering.
LEARNING ACTIVITY 1 – MECHANICAL WEATHERING (Part I)
1. Explain that weathering involves two processes that generally work together to decompose rocks at or near the earth’s surface: mechanical weathering and chemical weathering.
2. Place an effervescent antacid tablet on a table and break it with a hammer. Explain that this is a form of mechanical weathering-the physically breakdown of rocks into smaller fragments without changing their chemical composition. Ask: What are some things that might cause mechanical weathering? (Answers will vary but may include: extreme heat, extreme cold, exfoliation, crystal growth, the growth of lichens and plant roots-also called biological weathering-and human and animal traffic.)
3. Have students log onto the “Types of Mechanical Weathering” Web site and click “next” twice, which should take them to the “Mechanical Weathering – Exfoliation” page. For this and the next four pages of the Web site, provide students with a FOCUS FOR MEDIA INTERACTION by asking them to complete the “Mechanical Weathering Student Organizer” (PDF)(RTF). Allow ten minutes for completion of the organizers.
4. Review the students’ answers to the organizer questions, correcting and explaining as necessary (Answer keys to all student organizers are available in the Materials list on the Overview page). Ask if they can think of any other types of mechanical weathering. (Answers will vary.) Tell them that in temperate climates like our own, frost wedging is one of the most common types of mechanical weathering. Explain that this is a different process than the thermal expansion and contraction they just learned about. Tell students that they will now be conducting a demonstration that will illustrate how frost wedging works.
5. Ask two student volunteers to come to the front of the class. Have one student fill a balloon with water until it is the size of a ping-pong ball, and then tie a knot at the end. Have another mix water with plaster of Paris; once the mixture is as thick as yogurt, have him or her pour half of the plaster in one milk carton and the other half in the other. Have the student with the balloon push it down into the plaster in one carton until the balloon is about 1/4 inch under the surface. Have him or her hold the balloon there until the plaster sets enough so that the balloon doesn’t rise to the surface. Let the plaster harden for about 1 hour. Put both milk cartons in the freezer overnight.
6. Ask students to predict what they think will happen when the milk cartons are frozen? (Accept all answers.) Tell students that they will see tomorrow what happened. Explain that in the meantime they will be looking at the other primary type of weathering: chemical weathering.
LEARNING ACTIVITY 2 – CHEMICAL WEATHERING
1. Explain that chemical weathering describes a process in which rock is broken down through a change in its chemical composition-most commonly through the dissolution of minerals in the rock by water. One common form of chemical weathering is oxidation of iron in rocks-otherwise known as rust. Another is when carbon dioxide from air combines with water to form carbonic acid, which dissolves rock-especially rock containing high amounts of the mineral calcium carbonate (e.g. marble or limestone).
2. Illustrate this last point by dropping an effervescent antacid tablet into a beaker of water. Explain as it dissolves that these tablets contain sodium bicarbonate which dissolves in water in much the same way that carbonate rocks dissolve in carbonic acid. Ask students if they think that temperature is a factor in chemical weathering? (Accept all answers.) Tell students that they will now be conducting an experiment to determine how the rate of chemical weathering might be affected in different climates around the world.
Divide the class into groups of 4-5 students. Distribute to each group an empty 250ml beaker, a 1000ml beaker filled with hot tap water, a tray of ice, a thermometer, a stopwatch, and the “Chemical Weathering” student organizer (PDF)(RTF).
3. Have each group combine some ice and hot water in their empty beaker until the temperature reaches the 40-50° C range, at which point any remaining ice in the beaker should be removed. Ideally, the total volume in the beaker should be about 200ml, although a little less or more won’t matter. Record the temperature of the water on the organizer.
4. Have one member of each group start timing with a stopwatch at the moment another group member drops an antacid tablet into the beaker. Stop the stopwatch when the tablet has completely dissolved and no traces of the tablet are visible. (Don’t wait for the bubbling to stop.) Record the dissolving time in the organizer. Also record the water temperature again; calculate the average temperature during the experiment (i.e. add the starting and final temperatures and divide by 2) and enter that into the organizer.
5. Empty the beaker (rinsing well to get rid of any antacid remnants) and repeat the experiment four more times, lowering the temperature range each time by 10 degrees (i.e. round two of the experiment should be 30-40° C, round three should be 20-30° C, and so on.) NOTE – if you are short on time, assign different temperatures to different groups of students rather than having all the groups repeat the experiment four times.
6. Direct students to the “Graphing Tutorial” Web site, providing a FOCUS FOR MEDIA INTERACTION by asking students which types of graph would be best suited to easily and effectively plot the data they’ve just collected. (A bar or line graph would be simplest and best.) Which would be least suitable? (A pie chart would be unsuitable as it does not reflect changes over time.) Have each group graph their tablet dissolution time answers in a bar or line graph on their graph paper (where the X axis is the Average Water Temp and the Y axis is Dissolving Time).
7. Have students answer the questions at the bottom of the organizer.
8. Ask students what else might accelerate the chemical weathering process they just modeled? Offer the hint that they learned about it earlier in the lesson. (Mechanical weathering.) Pull out another antacid tablet and crush it with a hammer. Drop the crushed bits into water-they will dissolve almost instantly. Explain that this shows how mechanical weathering facilitates the chemical weathering of rocks.
9. Ask students if they think the opposite is true (i.e. that chemical weathering facilitates mechanical weathering)? (Yes.) Have each group drip a few drops of water on antacid tablets-just enough to start its fizzing reaction. After a few seconds, have them rub the dissolving tablet between their fingers. Explain that the antacid residue coming off on their fingers shows how chemical weathering (i.e. the water dissolving the tablet) can facilitate mechanical weathering (i.e. the fingers rubbing-or abrading-the tablet).
DAY TWO – LEARNING ACTIVITY 1: MECHANICAL WEATHERING (Part II)
1. Review the previous activity’s experiment with the milk cartons. What were students’ predictions about what would happen when they froze? (The plaster containing the balloon should have cracked as the water in the balloon froze and expanded.) Remove the plaster-filled milk containers from the freezer. Ask students: what happened to the plaster that contained the balloon? (It cracked.) What happened to the plaster that had no balloon? (It did not crack.) Why the difference? (The water in the balloon expanded as it froze.) Explain that this is the same process which occurs when water seeps into cracks in rocks and freezes-a process called frost wedging.
2. Have students log on to the “Types of Mechanical Weathering” Web site and have them click “next” until they get to the “Frost Wedging” page. Provide students with a FOCUS FOR MEDIA INTERACTION by asking them to find the name of the process that describes how small frost wedging cracks can become larger over time? (The freeze-thaw cycle.) Ask a student volunteer to describe this process. (As water frozen in rock cracks thaws, it seeps deeper into the cracks it made when it froze before; when it freezes again, it widens the crack.)
LEARNING ACTIVITY 3: EROSION
1. Explain that once a particle of sediment loosened by any type of weathering is somehow transported somewhere else, the process is called erosion. Ask the class to name forces that might drive that movement, writing them on the blackboard or whiteboard. (Answers may include wind, water, ice, and gravity. Accept all.)
2. Explain that the class will now be taking a closer look at these forces that drive erosion. Distribute the “Erosion” student organizer (PDF)(RTF). Have students log onto the “Erosion and Weathering” Web site and click “view” at the center of the page. Provide a FOCUS FOR MEDIA INTERACTION for students by explaining that each of seven pages on the site has one corresponding question on the organizer, which they will have 5 minutes to complete.
3. Review the organizer questions with your students, correcting or clarifying their answers as necessary. Ask the class if they think all major factors of erosion were covered by the Web site (Accept all answers). Explain that water is an erosive agent not just in streams (where it forms V-shaped valleys), but along coasts, where wave action erodes shorelines over time. Explain that glaciers also scrape away the landscape (forming U-shaped valleys) as they move over time. Tell students that they will now be watching a video clip that describes the action of one of the most important forces behind erosion. Provide students with a FOCUS FOR MEDIA INTERACTION by asking them to form a hypothesis about whether the massive Hawaiian costal cliffs they’ll be seeing were mainly created by water erosion (i.e. like a river bank).
PLAY Clip 1, “Hawaiian Coastal Cliffs” (access the video segments for this lesson at the Video Segments Page).
4. Review the focus question: Were the Hawaiian coastal cliffs mainly created by coastal water erosion? (No. They were created by gigantic landslides.) What is the main force behind a landslide? (Answers may vary and might include Hawaii’s volcanic/tectonic activity, but explain that gravity is always the prime mover of any landslide-the geological term for which is “mass wasting.” Explain that gravity also promotes erosion through the downward flow of water and ice, which is one of the most important forces behind erosion.)
5. Explain that, in addition to being an inherently unstable volcanic land mass, Hawaii has a tropical climate: hot, humid, and rainy. Based on their chemical weathering experiment yesterday, ask students if they think chemical weathering is common there? (It is.) What type of erosion is probably most common? (Water erosion.) Tell students they will now be looking at another clip, which shows the effects of Hawaii’s heavy rainfall on its terrain. Provide a FOCUS FOR MEDIA INTERACTION by asking students to write down three places where the clip shows water flowing.
PLAY Clip 2, “Water Erosion” (access the video segments for this lesson at the Video Segments Page).
6. PAUSE the clip after the shot with the child and the boulder. Review the FOCUS question: Name three places in the clip where water is flowing? (A road, a river, and a waterfall.) Explain that all three represent channels, which confine the flow of water into a stream, and that this confinement increases the water’s velocity. Distribute copies of page 6 of the NY State Earth Science Reference Tables PDF and direct students’ attention to the “Relationship of Transported Particle Size to Water Velocity” chart.
Ask students what they can conclude about the capacity of higher velocity streams to carry sediment particles. (The greater the velocity of a stream, the larger the sediment particles it can carry.) Explain to students that Hawaii’s mountainous terrain tends to create high-velocity streams such as they’ve just seen in the video, and that this renders the landscape highly susceptible to water erosion.
7. Provide a FOCUS FOR MEDIA INTERACTION for the remainder of the clip by asking students to note measures Hawaiians have taken to prevent waterlogged hillsides from falling onto their homes.
PLAY Clip 2, “Water Erosion” through to the end.
Review the focus question: What measures have Hawaiians taken to prevent their homes from landslides? (Steel mesh draped over hillsides.) Ask student to name the term from the “Erosion and Weathering Web” site that describes this. (Erosion management.) Ask if the mesh will prevent weathering. (No-it will only temporarily control erosion. The mesh will do nothing to protect the soil from the physical and chemical weathering effects of rainfall.)
9. Tell students that they will now be reviewing what they’ve learned about the major forces and factors of erosion and weathering.
1. Load and project the Web site for “Weathering and Erosion Jeopardy” and tell students that they will be playing a Jeopardy-style game designed to review their understanding of key terms in the game’s first two subject categories-”Weathering” and “Erosion.” Divide the class into three groups, and have each group select one member to be its representative, or “contestant.”
2. Distribute a “Weathering and Erosion Jeopardy Student Organizer” (PDF)(RTF) to each group. Provide a FOCUS FOR MEDIA INTERACTION by explaining that for each point value selected by a contestant from either category, the game will give a definition. Groups may confer with their contestants about the correct answer, but once one of the contestants has raised his or her hand, all discussion must stop, and that contestant must give a term (phrased as a question!) corresponding to the definition. If he or she answers correctly (which should be checked against the “Erosion Jeopardy Answer Key”), scroll down in the game’s lower window to reveal and confirm the answer, and add that question’s point value to his or her group’s score. If the answer is incorrect, those points are deducted from the group’s score, and the other two contestants are free to raise their hands and attempt to answer. Use a blackboard or whiteboard to keep score, and have each group write down each question and correct answer on their “Weathering and Erosion Jeopardy Student Organizer.”
Have students research the Dust Bowl of the 1930s, when much of the American Great Plains suffered catastrophic wind erosion after protective prairie grass was removed and the soil loosened to support overly-intensive agriculture.
Have students study and model other chemical weathering reactions common in nature. Possible experiments could include the corrosive effect of acid rain.
Invite a civic engineer, landscape architect, or farmer to speak to the class about the various types of erosion and management and prevention strategies in the local environment.