Geology Cafe

Landslide Hazards—An Awareness Guide

Table of Contents

Laboratory Activity: Make Your Own Landslides and Alluvial Fans


Objectives: This laboratory activity illustrates processes associated with landslides and debris flows in mountain canyon areas. The activity also illustrates how sediments are deposited and sorted by flowing streams on alluvial fans. The laboratory activity is intended to show students how different kinds of materials (gravel, sand, and soil) behave in response to flooding in a confined stream channel area and on different angles of slopes. The experiments also allow students to observe how alluvial fans form at the mouths of canyons in mountainous area. This laboratory should be used as a basis for inquiry about landslide, debris flow, and alluvial fan processes in the vicinity or region where students live or travel.

Learn more about alluvial fans.

Below is an illustration of a sample landslide flume setup used in this lesson's laboratory activities. One workstation is recommended for a group of 4 to 8 students.

Materials needed for each work station
  • 1 gutter section (at least 3 feet)
  • 1 low rim plastic basin (10 gallon size or more recommended)
  • 1 gallon plastic container (jug)
  • 1 pencil (to plug holes in water jug)
  • A “flume” prop (bricks, wood, or other objects to prop up the end of the flum)
Additional Materials (to share with all workstation groups)
  • 1 bag of sand
  • 1 bag of small gravel (average about 2-4 mm or 0.3 inch diameter average)
  • 1 bag of potting soil
  • large pebbles (a selection of 2-3 inches in diameter rounded and angular pieces)
  • Plastic Monopoly houses and hotels (small pieces of wood could be used to substitute)
  • Tin Foil
  • Saran wrap
( Note: a standard 10 ft. plastic gutter section costs about $5 and can be cut with a saw into three 39 inch troughs.)
Clean-up maintenance suggestions
  • The best thing to do is to conduct this activity outdoors on a playground or school grounds near the classroom.
  • Having buckets available to reuse or recycle used sand, gravel, and soil is recommended.
  • A garden hose and a broom might be needed for clean up.
  • A plastic tarp beneath each workstation could help confine any mess.
Preparing Students For the Landslide Activites
  • Students should already have been introduced to concepts relating to the rock cycle erosion, deposition, sediments and sedimentary rocks, mountain building, volcanism).

  • Students should be aware of the different on types of natural hazards (earthquakes, volcanic eruptions, tsunamis, floods, hurricanes, and wildfire).

  • Present information to students in the 4 introductory websites:
  • Students should already be introduced to the concepts of landslides hazards, types of landslides, debris flows and debris floods, and alluvial fans. Selected photographs and discussions are on the Image Gallery website. Some of these images could incorporated into a PowerPoint presentation, or printed and hung around the classroom.

  • Students should understand that the flume setup it intended to mimic a narrow canyon with an alluvial fan (basin area) at the mouth of canyon. The controlled floods generated in the experiments are intended to simulate storm events. The Monopoly buildings (or substituted items) are intended to represent urban development (they also bring a interest-generating sense of suspense to the experiment outcomes and discussions).

  • Students will need to keep organized notes about what they observe happening in the flume and in the basin. They will need to count events in seconds and record how long "events"take place in the flume, such as how many seconds it takes for the first water or "landslide"to fall into the basin? Or, when did the activity stop? Or, when and how did the objects move in the flume or fall into the basin?

How to Use the Sediment Flume

For a typical class, 3 flumes are probably enough. Set up the flumes in a location where each group can see what the others are doing. Assign students for each group one of the following tasks:
 
2 students set up the sediments (sand, gravel, soil) in the flume (they can be called “the engineers”)
1 student sets up and manages the water jug (they can be called “the hydrologist”)
1 student places the “buildings” and other objects in the flume (they can be called “the developers”)
All the other students are observers and record keepers (they can be called “the science reporters”)

STEP I The first stage is to try to conduct a controlled experiment that each group would replicate, and then compare results. All the “variables” need to be exactly the same in each flume for the first experiment.
 
Each set up at exactly the same angle set with a gentle slope (about 15 degrees, or about 5 inches higher at 1 end for a 39 inch flume gutter). The same amount of sand should be added to each flume.

Start with 1 quart of dry sand. The sand should be evenly distributed down the flume to a depth of about ½ inch. (This should be done by the “engineers.”)
 
Monopoly buildings, or pieces of wood should be spaced about 6 inches apart down the flume (by the “developer”).
 
To create a flood, a pencil should be stuck in the bottom corner of a corner of milk jug (see photograph). Have the student (the “hydrologist”) pull out the pencil (they can use the pencil to block the hole again after the “landslide” is complete. The students should start counting out loud at one-second intervals while the “reporters” watch and take note as to what happens in the flume and in the basin. The count should continue until all the water flows through the trough, and materials settle into the basin.
 
Typically what will happen is that the water builds up in the trough and starts to erode and transport sediment down the flume, and if the angel is right, most or all of the material may eventually slip down the trough into the basin. With the exception of reusing the “buildings,” do not have the students touch the material in the basin. This is where an“alluvial fan” starts to form and build up with each subsequent experiment step.
 
Have students compare their results. How many seconds did it take for a landslide to occur? What kinds of things happened with the water, sediment, and buildings over time? How did the "flood"compare to a natural flood event? How did the results of one group compare with another?

Step II Have the “engineers” fill the trough again. This time, fill one trough with soil, one with gravel, and one with a mix of equal parts of soil+water+sand. Again, a quart of material spread through the trough about ½ inch deep. The “hydrologist” should refill the water jug (with pencils back plugged back in the holes). The “developer” should put the building back in at the same six inch spacing.
 
Again, pull the plug as the “observers” start counting. Compare and contrast how the materials behaved. How did the type of sediment affect the timing and behavior of the landslide (if one occurred)?

Lab sheets and tables for making trigometry calculations

Step III

From this point, students should use their observations to make their own experiments and observations (in the same controlled manner). Here are some suggestions:
  • Try changing the angle of the slope of the trough. Can you predict what will happen in advance?
  • Add more sediments to the flume. Can you predict what will happen in advance?
  • Try lining one of the trough with crumples tin foil. Line another with Saran Wrap or wax paper. How does the texture of the trough bed affect landslide and flood activity? How might this compare with a natural setting?
  • Build dams out of Saran wrap or modeling clay, or other materials. Or, create channels to attempt to redirect the flow. Try different materials. Did the dam hold back the flood or prevent a landslide (and why)? What worked, and what didn't?How to the impact the floods, landslides, or security of the "homes"in the flume?
  • Challange students to come up with the best designs to prevent damage to "homes"placed in the flume or on the alluvial fan in the basin. What worked, what didn't work?
  • Ask students to evaluate how the sediments behaved in the basin (alluvial fan). Did an alluvial fan build up? Did the sediments become sorted? Where did the coarse and finer materials go? What color was the water in the basin, and why?

Follow-Up and Conclusion

Be sure that students record their observations. Make sure they note how the sediment builds up on the “alluvial fan” at the base of the trough, and that the sediments will natural sort from coarse grained to finer grained away from the “canyon” (trough). Ask students to decide where the “safest place to build” in this setting. How do the different materials behave, and how to the movement of water and sediment change?

Possible homework assignments and assessments
  • Have students review this website, the USGS Landslide Hazards website [http://landslides.usgs.gov] and the FEMA Natural Hazards and Preparedness website [http://www.fema.gov]. When and where should individuals be concerned and prepared for landslide and debris flow hazards?

  • Have students write a short paper about the potential of landslide and debris flow hazards where they live. Is there an alluvial fan in your community? What is underneath the home, school, and community where you live?

  • Have students go to the library or search on the World Wide Web for examples of landslide disasters in the United State or in other countries. Be sure to have them clearly explain all the basic facts of the landslide catastrophe. Why did it happen? [The La Conchita, Portuguese Bend, Mussel Rock Park, and Mission Peak slides have impacted communities and much has been written about them.]

  • Have students investigate the connections between landslides activity, climate, and wildlife habitats. How did the El Nino climate cycle of 1998 affect landslide activity in California? Do landslides hurt or help salmon and other wildlife?

  • Have students explain why landslide disasters occur and what efforts might prevent or reduce the impact of landslide and debris flows. How and where is this done in their own community?

< Students preparing to unleash a flood in the flume.
 
http://geologycafe.com/landslides/activities.html
8/28/2012