Forms of bluffs degraded for different lengths of time in emmet county,Michigan, U.S.A.

Distinct differences in morphology are found among bluffs cut and abandoned by Glacial Lake Algonquin and by the Nipissing Great Lakes in Emmet County, Michigan and modern, active bluffs presently being eroded by Lake Michigan in Mason and Manistee Counties, Michigan. The Algonquin, Nipissing, and modern bluffs are all composed of a sandy, morainic material. Because the composition and mode of formation of the three sets of bluffs are similar, it is assumed that the abandoned bluffs had the same initial configuration as the modern bluff. The morphologic differences are likely a function of the different periods of time each bluff has degraded. With time, the angle of the bluff midsection decreased, the extent of the convex crest and the concave base increased, and the angle of the crest increased. This course of hillslope degradation is believed similar to that occurring elsewhere on heavily vegetated hillslopes underlain by cohesionless material and situated in temperate, humid climates. The morphologic changes may be understood in terms of an analytical model which assumes that the rate of change in elevation at a point on a hillslope profile is proportional to the profile curvature at that point.