Appalachian and Ardennes Levels of Erosion Compared

Abstract

In the course of detailed geomorphic studies in the Ardennes massif of Belgium, the writer devised a method for recognition of partial planation surfaces. The method rests primarily on the study of flat benches and flat-topped summits. The many erosion levels (up to ten in a vertical range of 250 meters) in the Ardennes show a clear relationship to the drainage net, and their extent depends much on the resistance to erosion of the substratum. The levels are characterized by near-horizontality and are commonly separated by quite distinct scarps. Field work in the Appalachians, where multiplicity of levels has been reported, revealed surfaces quite similar to those of the Ardennes. These surfaces are commonly separated by small vertical intervals. A departure from the Ardennes conditions in the Ridge and Valley Province seems due mostly to differences in the range of resistance of the various formations. The several levels are believed to represent imperfect cycles of erosion, but they must have extended laterally from the alluvial plains of the rivers in the form of faint slopes due to mass-wasting agents. Recognition of many closely spaced and somewhat pediment-like erosion levels in widely distant regions with temperate humid climate suggests modifications of W. M. Davis' classic theory of erosion cycles.