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Mass Wasting

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What is Mass Wasting?

Mass wasting is the downslope movement of rock, regolith, and soil under the direct influence of gravity. It is also the step that follows weathering. The combined effects of mass wasting and erosion by running water produce stream valleys.

Location, Location, Location

Mass wasting events occur in every state and U.S. territory. Nearly all occur in mountainous regions. What causes these events? Basically weak or fractured materials + steep slope = landslides.

USGS Landslide Overview Map of the Conterminous United States from https://landslides.usgs.gov/hazards/nationalmap/. Map is from Open-File Report 97-289 Digital Compilation of Landslide Overview Map of the Conterminous United States By Dorothy H. Radbruch-Hall, Roger B. Colton, William E. Davies, Ivo Lucchitta, Betty A. Skipp, and David J. Varnes, 1982 by Jonathan W. Godt


Not all mass wasting events occur in hilly or mountainous areas. Flat areas may not be as stable as they appear due to:

    Expansive soils
    Peat bog areas
    Loose sediment
    Uncompacted fill
    Quick clays
    Limestone caverns
    Active faults
    Subsiding areas

Flat land problems are amplified on hillsides

The Origins of Mass Wasting

There are many possible reasons behind why a slope might fail, but the number one cause is gravity. But there are other factors, which include:

  • Water
  • Steep Slopes
  • Vegetation
  • Geology
  • Earthquakes
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CSULA Department of Geosciences and the Environment
Pasadena City College Department of Geology    
    © Sonjia Leyva 2018