Angle of Repose

Carla Whittington and Dr. Eric M. D. Baer (derived from material originally published in Whittington and Baer, 2005)
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Summary

In this activity students measure the maximum slope at which grains are stable (angle of repose). They explore how different properties of the sediment influence slope stability and lead to different slope failures (mass movements). The results are then used to examine the nature, frequency, timing, and causes of landsliding events in Seattle.

Students make piles from a variety of sediments and measure (either with a protractor or using basic trigonometry) the angle. They examine sediments with different sizes as well as different angularities. They also add water to the piles to evaluate its impact.

Learning Goals

Angle of repose Upon completion of this exercise, students should be able to:
  • measure the angle of repose
  • determine how grain size, angularity, and water content impact the angle of repose
  • relate angle of repose to mass wasting types and causes
  • apply knowledge gained during the experiments to patterns of mass wasting in the Seattle area.

Context for Use

This is a short activity we use in a variety of classes including an intro to geohazards course, physical geology, and an intro level geomorphology course. There is no previous knowledge required.
This activity can be done in an hour to two hours in an introductory class.

Description and Teaching Materials

Angle of repose instructions and student worksheet (Microsoft Word 197kB Feb11 06) The complete directions for the students are here, along with spaces for them to write in answers. I have them put all their answers on one sheet of paper, which is the back page, to facilitate grading. It also allows them to keep their directions and notes for review.

Teaching Notes and Tips

Students need to be warned to take their measurements with care and precision. If they are little off, they could have difficulty answering the questions well. Also, students tend to make small piles which increases error. (This is a terrific place to discuss error and propagation of error).

This activity requires some additional materials:
  • sand
  • rounded gravel
  • angular gravel
  • coarse gravel
  • protractors and rulers
  • trays to contain the experiments

The gravel can be easily purchased at a pet shop - aquarium gravel works wonderfully. Most hardware or home improvement stores sell sand and gravel as well.

Assessment

I grade the submitted worksheet.

References and Resources

I highly recommend the students use trig to determine the angle of repose. The trigonometry page can be a useful resource for this.