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<br /> <br />Debris Fan <br /> <br />A OEI3i{IS FAI~ is a sloping, wedge-shaped deposit of loose <br />rOCK, earth and vegetative debris near or at the junction of <br />a smaller stream 'iiith a larger stream valley, or where the <br />gradient of a stream abruptly decreases. It is created by <br />debris flows--the downstream/downslope propulsion of rocks, <br />vegetative matter, junk and other material in a watery, muddy <br />slurry. The stream which deposited the fan normally <br />traverses or runs along one of the edges of the fan. <br /> <br /> l <br /> '.~~ " <br /> '0 . .' <br />1 '" <br />'" 2 <br /> <br /> <br /> <br />. <br /> <br /> <br />. <br /> <br />. <br /> <br />:5 <br /> <br />4 <br /> <br />Debris/mud flow fans frequently offer scenic bui Iding sites In mountain valleys. <br />This case illustrates the following sequence. 1l A time in the past, shortly <br />after a debris flow that removed many of the trees and left the channel on one <br />side of the fan. 2) Some years later the soi I and vegetation have recovered and <br />the fan shows I ittle evidence of past debris flow events. 3) Man develops the <br />fan area with housing. 4) An intense cloudburst causes a debris flow which <br />destroys structures and vegetation and moves the channel to a new location unti I <br />the next event. <br /> <br />16 <br />