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<br />OD2795 <br /> <br />Debris avalanche: <br /> <br />Varnes (1978) <br /> <br />classifies these as <br />In comparing debris <br /> <br />a variety of very rapid <br />avalanches to debris <br /> <br />to extremely rapid debris flow. <br />flows he says, <br />"In debris avalanches, progressive failure is more rapid, and the <br />whole mass, either because it is quite wet or because it is on a steep <br />slope, liquefies, at least in part, flows, and tumbles downward, <br />commonly along a stream channel, and may advance well beyond the foot <br />of the slope. Debris avalanches are generally long and narrow and <br />often leave a serrate or V-shaped scar tapering uphill at the head, <br />in contrast to the horseshoe-shaped scarp of a slump." <br /> <br />Mudf10w: The term mudf10w is generally used to describe mass movements that <br />have the speed and characteristics of a debris flow and the consistency of a <br />very wet earthf10w. In fact, types of flows are distinguished mostly on the <br />basis of viscosity and shear strength. <br /> <br />Earthf10w: These ground failures have a characteristic "hourglass" shape <br />(figure ). A bowl or depression forms at the head where the slope material <br />liquefies and runs out. The flow itself is elongate and usually channelized <br />and'spreads out at the toe. Generally flows occur in fine-grained materials <br />or clay-bearing rocks on moderate slopes and,under saturated conditions. <br />Although dry flows of granular material are common. <br /> <br />Rapid earthflows usually occur in fine-grained silt, clay, and clayey sand of <br />marine orlgln. They are similar to lateral spreads except they involve not <br />only liquefaction of the underlying materials, but also retrogressive failure <br />and liquefaction of the entire slide mass (Varnes, 1978). <br /> <br />Human and Environmental Factors Affecting Landslides <br /> <br />Both natural and human-induced changes in the environment can affect <br />landslides. The geo109ic history, as well as activities associated with human <br />occupation directly determine, or contribute to the conditions that lead to <br />slope failure. <br /> <br />Human activities: These are mainly associated with construction and involve <br />changes in slope and in the surface and groundwater regimes. Changes in slope <br />result from terracing for agriculture, cut-and-fil1 for highways, buildings <br /> <br />- 9 - <br />