Simple Landslide Demo

Kate Scharer

Appalachian State University

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Initial Publication Date: April 30, 2008 | Reviewed: October 22, 2012 (see revision history: 2 events)

Summary

Demonstration of control of surface friction on slope stability. Simple analogue model uses a wooden board (the slope), a large rock (the landslide), and transparency and rough sand paper. Students anticipate how material roughness changes slope at which rock will slide.

Mass Movement, Geomorphology, Mass Wasting | College Introductory

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Context

Audience

Large (50-100 students) lecture section of environmental geology course for non-majors (largely non-science majors). Class has separate 2 hr/week lab.

Skills and concepts that students must have mastered

Types of mass wasting, force, stress, normal and shear stress, simplified slope stability equation, resisting and driving forces.

How the activity is situated in the course

In-class demonstration, ~5 minutes.

Goals

Content/concepts goals for this activity

Role of friction in slope stability

Higher order thinking skills goals for this activity

Formulation of hypothesis: will rock move at larger or smaller angle compared to other experimental set up?

Translation of force balance diagram and slope stability equation into physical model.

Other skills goals for this activity

N/A

Description of the activity/assignment

After brief introduction to landslides and slope stability maps, I prompt students to identify factors that control slope stability. I then explain force balance diagram and a slope stability equation I have modified for this audience:

Critical shear stress = friction * [(weight stress*cos (slope angle))—fluid stress]

And discuss the physical properties encompassed by each of the terms. This in-class demonstration was designed to illustrate some of the physical properties encompassed in "friction" term. [I also go through many calculations and effects of changing terms on critical shearing stress.]

Materials:

2 boards connected by door hinge
Large rock (or brick)
50-grit (course) sandpaper (1 sheet)
1 sheet of overhead transparency
String
Portable white board or sheet of cardboard
Marker

Procedure Start with rock on board, raise board. When rock slides, stop raising board and trace slope of board on whiteboard/cardboard (see picture in supplementary materials). Discuss concept of maximum slope angle. Show students sandpaper, prompt for hypothesis on change in maximum slope angle. Tie sandpaper around rock (quick and easiest method), run experiment again. Repeat with transparency. Discuss difference in smoothness/material properties on maximum slope angle.