Objective: Students will understand that a landslide occurs when the stability of a pile of dirt (angle of repose) is overwhelmed. By using various materials students can also understand how the addition of various materials can change the surface of the earth resulting in a landslide.
Materials: a piece of wood about 1/2 meters in length and 30cm wide, meter stick, block or brick, dirt, pebbles, small sticks, water, books on which to rest the board, pencil, chart to record information
Note that students should have science notebooks and/or graphic organizer to help record their observations. They should record what they do and see in words and illustrations.
1. Place the board at a small angle and rest the block upon it. Students should see that the block is at its “angle of repose” because it is stable and not moving.
2. Slowly raise the angle of the board and let students see that as the angle increases the block begins to move as the static friction is overcome. Students should measure the height at which the block moves.
3. Now put the board down at a low angle again and put a small amount of dirt on the board. The dirt will stay in place again showing that it is stable.
4. If you begin to slowly add more dirt to the pile it will eventually fall over and begin to cascade down the slope.
5. Clear the board and set it up again with a small amount of dirt. Slowly lift the board up increasing the angle of the slope. At some point the “angle of repose” will be overcome and the pile will slide.
6. Have students discuss their observations and conclusions about what starts an avalanche.
Extension: Repeat the demonstration using just pebbles. Then add pebbles to the dirt, small sticks, and finally water.
Have students research ways to stop avalanches and what safety precautions are recommended.