Retreat of lakeshore Bluffs

From a qualitative descriptive approach of the analysis of retreat of lakeshore bluffs, the key factors in failure and retreat are determined to be wave action, currents, wind, surface runoff, subsurface flow and sapping, raindrop impact, frost action, gouging by ice, chemical weathering, composition of materials, vegetation, lake levels, and shore protective structures. It is concluded that failure of bluffs need not lead immediately to retreat, but usually does so ultimately. In fact, retreat need not result solely from failure; i.e., from landslides. Cumulative resistance of glacial tills to all types of erosion is shown to be intermediate between that of bedrock and lacustrine materials, although in many areas, particularly where wave attack is dominant and the tills develop nearly vertical faces, the retreat of till bluffs does not differ significantly from that of shale bluffs. The cumulative resistance to erosion of a bluff in which a combination of materials is exposed is shown to depend, in most instances, on the resistance to wave attack and ice push of the material exposed at lake level. Quantitative data on soil and rock properties, available only in small quantities, are consistent with the behavior of corresponding materials in lakeshore bluffs.