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Hillslope Gradient-Particle Size Relations: Evidence for the Formation of Debris Slopes by Hydraulic Processes in the Mojave Desert

1985; University of Chicago Press; Volume: 93; Issue: 3 Linguagem: Inglês

10.1086/628956

1537-5269

Athol D. Abrahams, Anthony J. Parsons, Paul J. Hirsh,

Soil and Unsaturated Flow

This study is concerned with debris slopes free of superincumbent cliffs or basal stream channels and developed on closely jointed and/or mechanically weak rocks in the Mojave Desert. Analyses of the relation between hillslope gradient S and mean particle size $$\bar{D}$$ reveal that the slope coefficient of the relation varies with debris slope plan form and, where plan form is constant, the intercept varies with rock type. A theoretical model is developed which shows that the observed pattern of variation in the slope of the S-$$\bar{D}$$ relation with plan form is consistent with the debris slopes being formed by and adjusted to hydraulic processes. Debris slopes in the Mojave Desert appear to lie along a continuum. At one end are debris slopes underlain by closely jointed and/or mechanically weak rocks, such as those examined in this study, that are transport-limited, well adjusted to present hydraulic processes, and exhibit a strong relationship between S and $$\bar{D}$$. At the other end are debris slopes developed in widely jointed and mechanically strong rocks, such as those investigated by Oberlander, that are weathering-limited, poorly adjusted to contemporary hydraulic processes, and display little or no relationship between S and $$\bar{D}$$.