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10: Mass Wasting

  • Page ID
    32224
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    Learning Objectives

    At the end of this chapter, students should be able to:

    • Explain what mass wasting is and why it occurs on a slope.
    • Explain the basic triggers of mass-wasting events and how they occur.
    • Identify types of mass wasting.
    • Identify risk factors for mass wasting events.
    • Evaluate landslides and their contributing factors.
    Massive landslide flows through the center of the photo. A river terminates at the landslide on the left.
    Figure \(\PageIndex{1}\): The 1983 Thistle landslide (foreground) dammed the Spanish Fork River creating a lake that covered the town of Thistle, Utah. The slide covered Hwy 6 and the main railroad between Salt Lake and Denver. (By R.L. Schuster; public domain via Wikimedia Commons.)

    This chapter discusses the fundamental processes driving mass wasting, types of mass wasting, examples, and lessons learned from famous mass wasting events, how mass wasting can be predicted, and how people can be protected from this potential hazard. Mass wasting is the downhill movement of rock and soil material due to gravity. The term landslide is often used as a synonym for mass wasting, but mass wasting is a much broader term referring to all movement downslope. Geologically, a landslide is a general term for mass wasting that involves fast-moving geologic material. Loose material along with overlying soils are what typically moves during a mass wasting event. Moving blocks of bedrock are called rock topples, rock slides, or rock falls, depending on the dominant motion of the blocks. Movements of dominantly liquid material are called flows. Movement by mass wasting can be slow or rapid. Rapid movement can be dangerous, such as during debris flows. Areas with steep topography and rapid rainfall, such as the California coast, Rocky Mountain Region, and Pacific Northwest, are particularly susceptible to hazardous mass wasting events.

    • 10.1: Slope Strength
      Mass wasting occurs when a slope fails. A slope fails when it is too steep and unstable for existing materials and conditions. Slope stability is ultimately determined by two principal factors: the slope angle and the strength of the underlying material. Force of gravity, which plays a part in mass wasting, is constant on the Earth’s surface for the most part, although small variations exist depending on the elevation and density of the underlying rock.
    • 10.2: Mass Wasting Triggers and Mitigation
      Mass-wasting events often have a trigger: something changes that cause a landslide to occur at a specific time. It could be rapid snowmelt, intense rainfall, earthquake shaking, volcanic eruption, storm waves, rapid-stream erosion, or human activities, such as grading a new road. Increased water content within the slope is the most common mass-wasting trigger. Water content can increase due to rapidly melting snow or ice or an intense rain event.
    • 10.3: Landslide Classification and Identification
      Mass-wasting events are classified by type of movement and type of material, and there are several ways to classify these events. The figure and table show the terms used. In addition, mass-wasting types often share common morphological features observed on the surface, such as the head scarp—commonly seen as crescent shapes on a cliff face; hummocky or uneven surfaces; accumulations of talus—loose rocky material falling from above; and toe of the slope, which covers existing surface material.
    • 10.4: Examples of Landslides
      This page contains various examples of landslides, including details such as causes, effects, and severity.
    • 10.S: Summary

    Thumbnail: Talus cones produced by mass wasting, north shore of Isfjord, Svalbard, Norway. (Public Domain; Wilson44691).


    This page titled 10: Mass Wasting is shared under a CC BY-NC-SA 4.0 license and was authored, remixed, and/or curated by Chris Johnson, Matthew D. Affolter, Paul Inkenbrandt, & Cam Mosher (OpenGeology) via source content that was edited to the style and standards of the LibreTexts platform.