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Mass Wasting

What Can We Do About Mass Wasting?

In a natural setting, mass wasting presents little threat. Most slopes are relatively stable most of the time. However, when people modify slopes—their gravitational loads, or their water content—they may become unstable and fail. Engineers can study the stresses acting on a slope, test the material of which it is made, make some assumptions about behavior with higher pore pressure, etc., and predict how likely that slope is to fail if the additional load of a house were added to it. This study might conclude that the slope would still be stable, and so the house might be constructed. Later, after it has changed hands a few times, a new owner might decide to put in a swimming pool. A neighbor in the property just downhill, might decide to cut into the slope in order to widen a driveway, or a neighbor just uphill might inadvertently introduce large amounts of water into the ground while trying to maintain a gracious green lawn. Any one of these actions could bring the slope close to where it is unstable. A period of heavy rain could provide the final impetus, and a sudden mass wasting event could occur. To avoid such problems, property owners on such slopes must have their freedoms restricted. One way to accomplish this is to prohibit certain activities through zoning, deed restrictions, or insurance requirements. A less satisfactory means is by threat of litigation.

Resources

Books

Cooke, Ronald U. Geomorphological Hazards in Los Angeles: A Study of Slope and Sediment Problems in a Metropolitan County. London; Boston: Allen & Unwin, 1984.

Costa, John E., and Gerald F. Wieczorek, eds. Debris Flows/Avalanches: Process, Recognition, and Mitigation. Boulder, CO: Geological Society of America, 1987.

Haneberg, William C. and Scott A. Anderson, eds. Clay And Shale Slope Instability. Boulder, CO: Geological Society of America, 1995.

Press, Frank, and Raymond Siever. Understanding Earth. New York: W.H. Freeman and Co., 1994.

Small, R.J., and M.J. Clark Slopes And Weathering. Cambridge; New York: Cambridge University Press, 1982.


Otto H. Muller

KEY TERMS


Angle of repose

—The slope made by a pile of loose material, such as the sand in an hour glass.

Avalanche

—A mass movement in which a chaotic mass of rock and/or soil very rapidly flows down slope along a discrete surface; an avalanche is a type of flow.

Creep

—A mass movement that involves gradual downslope movement (flow), too slow to be observed directly, but apparent in many long term observations.

Erosion

—Movement of material caused by the flow of ice, water, or air, and the modification of the surface of the earth (by forming or deepening valleys, for example) produced by such transport.

Flow

—A mass movement process in which a chaotic mass of Earth material moves down slope; rates of flow are a function of fluid content of the mass and the grain size the higher the fluid content and finer the particles, the faster the flow.

Landslide

—A mass movement in which a fairly coherent mass of rock and/or soil rapidly moves down slope along a discrete plane; sometimes used to include all types of moderately rapid mass movements involving flows, falls, or slides.

Lateral spreading

—Mass wasting of water saturated sediments; lateral spreading involves the flow of finegrained sediments (clay, silt, or sand).

Pore pressure

—The pressure of fluids contained within the pores of a rock, which influences the strength of the rock and is often a factor in dramatic landslides or mudslides.

Rock creep

—Very slow mass movement of large rock fragments (pebbles, cobbles, and boulders) in response to the weight of overlying rocks.

Rock fall

—Very rapid mass wasting of large rock fragments that have fallen from an exposed cliff.

Slide

—A mass movement process in which a fairly coherent mass of rock and/or soil rapidly moves down slope over a discrete surface.

Slumps

—A mass movement process in which a fairly coherent mass of rock and/or soil moves down slope over a discrete surface, but curved (concave-upward) surface. Slumps occur much faster than creep but slower than slides.

Talus

—Large rock fragments that accumulate at the base of a steep slope, transported there by mass wasting.

Weathering

—Biological, chemical, and mechanical attack on rock which breaks it up and alters it at or near the surface of the Earth.

Additional topics

Science EncyclopediaScience & Philosophy: Macrofauna to MathematicsMass Wasting - Mass Wasting Processes, Moving Mountains To The Sea, Mass Wasting In Loose Aggregates, Mass Wasting In Rocks And Soils