Document type: DU ETD
Collection: Geology Theses  
Title The Morphology Of Slope Profiles: a Statistical Method To Critically Analyze the Slope Hypothesis Of Willeam M. Davis, Walther Penck, And Lester C. King
Author(s) Clark, Robert Owen
School/Department Department of Geography
Institution University of Denver
Degree Type Doctoral
Degree Name Ph.D.
Type of Resource text
Degree Date 1970-6
Digital Origin reformatted digital
Rights Statement All Rights Reserved
Reason for Restrictions No restrictions
Type of Restriction No restrictions
Keyword(s) Geology
Abstract The classical theory that stages in a fluvially-initiated cycle of erosion are marked by similar and well-defined slope configurations has been postulated by William M. Davis and Walther Penck. Lester C. King has offered a third interpretation of hillslope morphology and changes that occur with time. Although this “uniformitarian” approach to cyclical landform development continues to permeate the literature, its verity has been questioned by some students of hillslope evolution. The need for a definitive statement on the nature of valley-side profiles is therefore of fundamental concern to the science of geomorphology. The classical works of Davis, Penck, and King are reviewed in depth to present an unbiased appraisal of the three geomorphic theories. Recent studies on hillslope development are also presented to clarify the problems related to hillslope evolution. Statistical techniques were employed to test the validity of the classical geomorphic theories and are based on mathematical profile curves and regression models. These procedures were used to evaluate over 1,200 slopes selected at random from large-scale topographic maps of the western United States. Since the geomorphic concepts under investigation are theoretical, slope configurations that depict various stages of these cycles can be expressed as mathematical (or theoretical) curves. If it is assumed that the theories of Davis, Penck, and King are valid indicators of slope form throughout a physiographic region, it is then theoretically possible to predict the configurations of large numbers of slopes within the same region. On this basis slopes selected at random from “Test Areas” in the Pacific Mountains, the Intermontane Plateaus, and the Rocky Mountains were mathematically fitted with theoretical profiles representing the “mature” stages of the classical geomorphic theories. Regression equations for each theorist were computed from comparisons of actual and theoretical curves in the Test Areas and then used to predict profiles of randomly selected slopes in sixteen “Prediction Areas.” By statistically comparing the predicted forms with their actual counterparts, the reliability of each geomorphic theory can be tested. If the variance between these two sets of profiles is significantly large, it would be logical to conclude that such a geomorphic system is neither compatible with nor representative of one or more of the physiographic regions. Statistical analyses of the classical slope theories revealed that uniformitarian development is not an entirely valid concept for the western United States. Although results varied considerably among several theorists, the statistical findings were almost wholly negative. Mean deviation values derived from a comparison of actual and predicted declivities rarely dropped below 4 degrees; more often these values were as high as 6 or 7 degrees and even higher. The percentage variances between actual and predicted slopes were also largely negative for the five profile categories (convex, concave, convexo-concave, concavo-convex, and straight). The concavo-convex form was the only statistically significant and, hence, predictable profile. This profile was accurately predicted by King’s multiple-element model in the Pacific Mountains, Intermontane Plateaus, and Rocky Mountains with percentage variances of 1.8, 7.5, and 4.6, respectively. Although King’s multiple-element model was found to be a valid predictor of concavo-convex slopes, the three major profiles (convex, concave, and convexo-concave) were not representative of the Test and Prediction areas. The logical conclusion is that hillslopes are highly variable and reflect the vagaries of the environment; hence hillslopes cannot be categorized on the basis of rigid slope models.
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