6: Mass Wasting
- Page ID
- 33119
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This chapter defines what mass wasting is and then addresses what causes slopes to be stable and what factors contribute to slope failures. It also offers a way to classify mass wasting events and suggests ways in which humans intervene to reduce the likelihood of an event from occurring in a given area.
- 6.1: Factors that Control Slope Stability
- Slope stability is controlled by the slope angle and by the strength of the materials on the slope. Slope is a product of tectonic uplift, and strength is determined by the type of material on the slope and also by its water content. Rock strength varies widely and is also determined by internal planes of weakness and their orientation with respect to the slope. In general, the more water, the greater the likelihood of failure.
- 6.2: Classification of Mass Wasting
- The key criterion for classifying mass wasting is the nature of the movement that takes place. This may be a precipitous fall through the air, sliding—as a solid mass—either along a plane or a curved surface, or internal flow—as a viscous fluid. The type of material that moves is also important—specifically whether it is solid rock or unconsolidated sediments. The important types of mass wasting are creep, slump, translational slide, rotational slide, fall, and debris flow or mud flow.
- 6.3: Mitigating the Effects of Mass Wasting
- We cannot prevent mass wasting, but we can delay it through efforts to strengthen the materials on slopes. Strategies include adding mechanical devices such as rock bolts, or ensuring that water can drain away. Such measures are never permanent. We can avoid practices that make matters worse, such as cutting into steep slopes or impeding proper drainage. In some situations, the best approach is to mitigate the risks. In some cases, we need to stay out of the way.