Mass Wasting
Mass Wasting, is the failure and downslope movement of rock or unconsolidated materials in response to gravity. A landslide is a type of mass wasting event. An important reason for learning about mass wasting is to minimize risks from these events. Geologists, engineers, and others study the nature of the materials that fail, and how and why they fail. Using this knowledge, they classify mass-wasting events. In this chapter, we will learn more about the science behind mass wasting.
Mass wasting in Arizona is common; far more common than people think. The steepness of Arizona’s mountains, plateaus, mesas, and buttes, coupled with intense rain through monsoon events, provides the perfect landscape for mass wasting to occur. In the U.S., mass wasting events are a costly natural hazard, causing dozens of fatalities and ~$2 – 4 billions of damage to infrastructure, roads, buildings and homes annually (2). Below you can see some images of recent mass wasting events in Arizona.
Video 7.1 Select landslides in Arizona – translational, rotational, toreva blocks, slumps and debris flows. (00:56)
Arizona State Geological Survey, CC-BY
Learning Objectives
- Explain how slope stability relates to slope angle.
- Summarize the factors that influence the strength of materials on slopes, including type of rock, presence and orientation of planes of weakness such as bedding or fractures, type of unconsolidated material, and the effects of water.
- Explain what types of events can trigger mass wasting.
- List and describe the types of motion that can happen during mass wasting.
- Describe the main types of mass wasting—creep, slump, translational slide, rotational slide, fall, and debris flow or mudflow—in terms of the types of materials involved, the type of motion, and the likely rates of motion.
- Explain what steps we can take to delay mass wasting, and why we cannot prevent it permanently.
- Describe some measures that can be taken to mitigate the risks associated with mass wasting.
- Describe the mass wasting potential in Arizona.
The process in which rock, soil, or sediment moves down a slope under the force of gravity. Mass wasting is an umbrella term that includes hazards such as landslides, debris flows, rock falls, and mudslides.
A meteorological event that occurs during the summer and produces radical change in moisture conditions.
