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<br /> <br />table, reduce shear strength, increase the <br />weight of the soil mass, and may increase <br />erosion and freeze-thaw activity. Periodic <br />high-intensity precipitation and rapid snow- <br />melt can signifcantly increase slope instability <br />temporarily (Figure 7). <br /> <br />Erosion <br />Erosion by intermittent running water (gully <br /> <br />Figure 7. <br />The remains of a <br />house where three <br />children died in a <br />mudflow in Kanawha <br />City, West Virginia. <br />The movement was <br />triggered by heavy <br />rainfall from a cloud- <br />burst on July 9, 1973 <br />(Lessing et al., 1976). <br /> <br />10 <br /> <br />Figure 6. <br />Aerial view of the <br />Savage Island land- <br />slide on the east <br />shore of the <br />Columbia River, <br />Washington, 1981. <br />This landslide was <br />caused by irrigation <br />water (photograph <br />by Robert L. <br />Schuster, U.S. <br />Geological Survey). <br /> <br />ing), streams, rivers, waves or currents, wind, <br />and ice removes toe and lateral slope support of <br />potential landslides. <br /> <br />Weathering <br />Weathering is the natural process of rock deter- <br />ioration which produces weak, landslide-prone <br />materials. It is caused by the chemical action of <br />air, water, plants, and bacteria and the physical <br /> <br />