Landslides not only are dangerous causing more than 25 deaths
and over $1 billion in damages a year on average but are also widespread,
occurring in all 50 states. Compounding the hazards to humans, these natural disasters often occur along with other similar natural phenomena,
such as floods or earthquakes.
To minimize risk, the slope of land and the materials underground must
be considered when planning how to build in a community. Altering the
slope of the land, or even the amount of vegetation on a slope, can have dangerous consequences.
Consider: How might the slope of land determine development in a community? How might changing the slope of land by cutting through the land to build a road or housing project, for example create potential hazards for citizens?
1. Cover a flat surface, such as a lab table, with newspaper. Slowly
pour 500 mL of dry sand through a funnel onto the flat surface so that
makes a pile. Describe what happens to the sides of the pile as you pour the sand.
2. Hold a protractor upright (with the bottom edge held against the flat
surface) and carefully begin to 3. At the point where the curved upper
edge of the protractor intersects the surface of the pile of sand, read
the angle in degrees. This is the natural angle of the side (slope) of
the pile. Its
called the angle of repose. This is the steepest slope that can be formed in the material without the material slumping or sliding down the slope. Slide it behind the pile as shown in the diagram.
4. Repeat step 3 several times. Record the measurement of the angle of the slope each time.
Do you get the same angle each time? Why? Why is it important to make
this measurement several times? What do you think will happen to the
angle with a greater or lesser amount of sand? How might added water, as in heavy rains or flooding, affect the risk of sliding?
5. Repeat steps 1, 2 and 3 using different amounts of sand. Record the measurement of the angle of the slope each time. Does the angle of the slope change? If so, how much?
6. Pour extra sand onto a pile of sand several times. Record the measurement of the angle of the slope each time. Does the angle of the pile change?
7. Optional: Gather other materials such as coarse sand, clay or mud, gravel, silt, soil, table salt, and granulated sugar. Predict what will happen if you repeat steps 1-6 using these materials.
8. For each of these materials:
9. Record measurements on a chart. How do particle size and shape relate to the maximum slope angle the particles will maintain?
For local landslide examples, visit www.stategeologists.org and contact your state geological survey.