Chapter 10 Summary - Mass Wasting PDF

Chapter 10 Summary Mass wasting is the downslope movement of material under the direct influence of gravity. It may result in loss of life, as well as millions of dollars in damage annually. Mass wasting occurs when the gravitational force acting parallel to a slope exceeds the slo...

Chapter 10 Summary Mass wasting is the downslope movement of material under the direct influence of gravity. It may result in loss of life, as well as millions of dollars in damage annually. Mass wasting occurs when the gravitational force acting parallel to a slope exceeds the slope’s shear strength (the resisting forces that help maintain slope stability). The major factors causing mass wasting include slope angle, weathering and climate, water content, overloading, and removal of vegetation. It is usually several of these factors in combination that result in slope failure. Mass movements are generally classified on the basis of their rate of movement (rapid versus slow), type of movement (falling, sliding, or flowing), and type of material (rock, soil, or debris). Rockfalls are common mass movements in which rocks free-fall. They are common along steep canyons, cliffs, and road cuts. Two types of slides are generally recognized. Slumps are rotational slides that involve movement along a curved surface and are most common in poorly consolidated or unconsolidated material. Rock slides occur when movement takes place along a more or less planar surface, and they usually involve solid pieces of rock. Several types of flows are recognized based on their rate of movement (rapid versus slow), type of material (rock, sediment, or soil), and amount of water. Mudflows consist of mostly clay- and silt-sized particles and contain up to 30% water.  They are most common in semiarid and arid environments, and they generally follow preexisting channels. Debris flows are composed of larger particles and contain less water than mudflows. Earthflows move more slowly than either debris flows or mudflows, and they move downslope as thick, viscous, tongue-shaped masses of wet regolith. Quick clays are clays that spontaneously liquefy and flow like water when they are disturbed. Solifluction is the slow downslope movement of water-saturated surface material and is most common in areas of permafrost. Creep, the slowest type of flow, is the imperceptible downslope movement of soil or rock. It is the most widespread of all types of mass wasting. Complex movements are combinations of different types of mass movements in which no single type is dominant. Most complex movements involve sliding and flowing. The most important factor in reducing or eliminating the damaging effects of mass wasting is a thorough geologic investigation to outline areas susceptible to mass movements. Although mass movement cannot be eliminated, its effects can be minimized by building retaining walls, draining excess water, regrading slopes, and planting vegetation. Key Terms Complex movement Permafrost Shear strength Creep Quick clay Slide Debris flow Rapid mass movement Slow mass movement Earthflow Rockfall Slump Mass wasting Rock slide Solifluction Mudflow