Sedimentation and geomorphic changes following the 1980-1983 eruptions of Mount St. Helens

Reduced infiltration and burial of surface roughness elements, together with the loss of root strength and reduced evapotranspiration associated with blast-toppled vegetation have dramatically accelerated erosion of blast-affected hill slopes. Other investigators have found that rill erosion rates were initially higher than the yearly average, but then declined sharply so that rill erosion rates during the second year were only 5 percent of the average first year rate. Initial rates of sheet erosion were substantially higher than the average rate for the year, but the rate of decline was not as pronounced as in the case of rill erosion (Swanson, et al., 1983b).


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