J. David Rogers INTRODUCTION TO SLOPE STABILITY AND LANDSLIDES

Landslide susceptibility map of the continental United States, taken from the U.S. Geological Survey.Landslide susceptibility map of the continental United States, taken from the U.S. Geological Survey. Worldwide annual landslide losses cost between US$10 and 20 billion per year, causing on average, about 1,000 deaths per year in the CircumPacific countries (from Schuster, 2003).Worldwide annual landslide losses cost between US$10 and 20 billion per year, causing on average, about 1,000 deaths per year in the CircumPacific countries (from Schuster, 2003).

Part 1 BASIC CONCEPTS OF SLOPE EQUILIBRIUM

Slopes in equilibrium with their environment typically exhibit concave, straight, and convex hillslope profiles shown at left. Slopes out-of-equilibrium typically exhibit anomalous, hummocky profiles, shown at right Concepts of Equilibrium

Stepped Topography Stepped topography is not necessarily indicative of slope instability, but can be structurally controlled by underlying stratigraphy, as shown here. Shales are most often associated with landslides.Stepped topography is not necessarily indicative of slope instability, but can be structurally controlled by underlying stratigraphy, as shown here. Shales are most often associated with landslides.

Out-of- Equilibrium Slopes Slopes that are experiencing rampant erosion are typically out- of-equilibrium, and exhibit truncated concave slope profiles, shown at left.Slopes that are experiencing rampant erosion are typically out- of-equilibrium, and exhibit truncated concave slope profiles, shown at left.

The slope profile is also influenced by runoff requirements and the relative position of controlling base level, as sketched here.The slope profile is also influenced by runoff requirements and the relative position of controlling base level, as sketched here. Note change in hill profile as channel moves away from the ridgelineNote change in hill profile as channel moves away from the ridgeline

Beginning of an erosive cycle. Note slight changes in hillslope profile

Continuation of an erosive cycle, with gradual shift of the hillslope profile, resulting in hummocky topography. Hummocky slopes are typical of slopes experiencing landslippage.

EXAMPLES OF HUMOCKY TOPOGRAPHY Hummocky topography is usually indicative of solifluction or active landslippage