Shaking and Landslides

Materials / Preparation

For each group of students, provide the following:

• one half gallon milk cartons or stream table;
• materials to develop your slope, e.g., wet sand
• newspapers
• large protractors
• source of shaking: electric sander, massager, etc.
• scale or balance (optional)

Grouping

Groups of three or four

Teacher tips

This activity is modified from the one shown at Landslides. This site focuses on landslides caused by water saturation. We have modified it to demonstrate landslides caused by shaking. The original lab asks you to pour water on the slope – instead, use a sander, electric massager, drill (anything that causes a consistent vibration) to initiate the landslide. Since degree of slope will influence the earthquake, consider having students elevate the slope to different angles – use large protractor to measure the amount of slope.

Students will need to apply a consistent shaking. Placing an electric sander, electric massager, or anything else that creates constant vibrations against the stream table is a good start. Students can also try to shake the table manually. The challenge with that is to ensure consistent shaking intensity. One way to accomplish this is to place a heavy object (e.g., small cardboard box filled with books or bricks) about an inch away from the stream table on both sides. That will limit the distance that students can shake the table from side to side. Do one or two trials like this.

Do the lab yourself before having the students do it. Prepare the wet sand, so that the amount of water is just sufficient to saturate the sand.

Procedures

1. Introduce the activity by asking students if any of them have seen or heard about landslides. Ask students where and when the landslide occurred and the effects it had.
2. Then ask students what they think causes landslides – record their answers on the board.
3. If they have not mentioned earthquakes as a cause, tell students that landslides are also caused by earthquakes, and that is what they will study in this activity. Ask the class to brainstorm a list of the different variables that trigger landslides, such as slope, material, and magnitude of earthquake (amount of shaking).
4. Tell students that they are going to design an experiment that will test these variables. Review the materials they’ll be using to simulate a small-scale landslide.
5. Divide the class into small groups and provide each team with the materials needed for the lab. Have them brainstorm how they will simulate the landslide and share their ideas with you before beginning. Remind students that they should test only one variable at a time—and carefully record the variable each time (for example, the angle of the slope, the amount of material used, or the amount of shaking). They will need to repeat their experiment three times, then average the results of each to obtain more accurate data.
   NOTE: See teacher tips (above) on consistent shaking.
   After each landslide has occurred, students should measure the distance the debris flow travels down the slope and/or its weight or volume.
6. Depending upon the amount of time you have, have students explore various parameters. They should begin by changing the amount of shaking. If your electric device has multiple speeds, use them. If you're doing shaking manually, move the two objects a bit further away from the stream table so that you can do higher amplitude shaking. Also, try shaking at different speeds (this is analogous to the frequency of seismic waves). You can also vary the slope angle. Compare the distance the debris flow travels down the slope for different shaking intensities and slope angles.
7. After the students have completed the lab, discuss the lab and elicit from students what they have learned from the lesson. If they have made measurements of extent of debris flow as related to slope, record results on board for class to see. Discuss.
   NOTE: Earthquakes “trigger” landslides. As the lab exercise hopefully demonstrates, shaking can make it easier for a landslide to initiate. The ultimate driving force of earthquake-induced landslides, however, is still GRAVITY. That’s why slope steepness is so important. If a slope is not steep enough, no amount of shaking will cause a landslide. The factors that affect the likelihood of regular landslides (water, slope steepness, rock type, lack of vegetation, human-altered hillslopes, etc.) all affect the likelihood that a landslide will be triggered by an earthquake. Mapping these factors allows us to predict the areas most at risk for land sliding.
8. Ask students to compare two hypothetical earthquakes:
   a. Earthquake during the rainy season,
   
   b. Earthquake during the dry season. Will more landslides occur from the rainy season earthquake, the dry season earthquake, or will they have the same? (Answer: Rainy season – water makes landslides more likely). You could extend this lesson by asking students to devise another experiment that would test this.
   

Resources used

Landslides
http://www.teachingboxes.org/catalog.jsp?id=DLESE-000-000-002-229