Chapter 8 - MASS WASTING

Beware of landslides

MASS WASTING: the downslope movement of rock, regolith, and soil under the direct influence of GRAVITY.

  • occurs practically anywhere in hill or mountainous terrane.

  • often violent, causes on immense disasters.

  • needs a trigger (ice melt, change in groundwater, earthquake)

    ANGLE OF REPOSE: the steepest slope materials can maintain (may be different if wet or dry) 25-40 degrees.

    TALUS SLOPE - accumulation of rock debris at the base of a cliff.


    Movement occurs downslope along defined surfaces; the type of slope, the kind of material (rock, cinders, mud, etc), and the amount of water (or ice) involved result in different forms: CREEP: the slow movement downslope due to repeated expansion and contraction of the surface (mostly ice, wetting and drying). The soil-covered slope of a hillside very slowly moves downslope to a creekbed at the bottom of a hill. Creep can cause soil to pile up against the side of a house, breaking its foundation. Trees that are bent at their base are an indication of creep.

    PERMAFROST: - zone of frozen soil in arctic regions and mountain tops. (Soil often directly overlies ice.) Building is a problem in areas of permafrost, because the heat of a house or a black road surface (heated by the sun) can cause permafrost to melt (i.e. sinking houses).

    SOLIFLUCTION - mass movement due to meltion of permafrost.

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