level and the associated erosion. Few changes in strand- line position can- 

 not be explained in this manner. 



b. Terrace Bluff . Although somewhat subtle in the topographic expres- 

 sion at some locations, the presence and absence of vegetation are excel- 

 lent indicators of the lakeward margin of the foredune or sand terrace. At 

 some sites it was impossible to distinguish where the landward extent of the 

 terrace terminated, especially when it was adjacent to low-lying dune areas. 

 It is the lakeward edge of this feature which most authors refer to as the 

 bluff (e.g., Seibel, 1972). The terrace is present throughout most of the 

 eastern coast; where it is absent, recession rates represent the true, 

 steep bluff of Pleistocene glacial drift. However, it is impossible to 

 determine accurate recession rates of the Pleistocene bluffs in many parts 

 of the coast because they are almost always steep and capped by mature 

 trees. As a result, the actual position of the bluff is masked on the 

 photos. In the present study this was the case only at site 15 and to a 

 lesser extent at site 5. 



Although data were only available for a few of the sites during the 

 1940' s, all showed no significant changes in the position of the terrace 

 bluff. The northern sites showed both accretion and recession during the 

 period 1952-58, a general decline in lake level (Fig. 8) with the range 

 from accretion of 3 feet per year to recession of 3 feet per year (Fig. 10, 

 left) . As expected, the period 1950-55 shows a marked recession of the 

 terrace bluff at the southern sites. Rates ranged from 5 to 13 feet per 

 year (Fig. 10, right). The photo coverage of the southern sites (Fig. 10, 

 right) includes the extremely high levels of 1952 in which is not the case 

 for the northern sites (Fig. 10, left). 



During the late 1950 's and early 1960 's there was either stability or 

 accretion at all sites with the majority showing accretion (Fig. 10, 

 left). Maximum rates were 10 feet per year. This is also to be expected 

 because of the general decline in the lake level toward the alltime low of 

 1964. 



The next period (1965-70) between photo coverage shows mixed changes 

 throughout the east coast of Lake Michigan. Sites 4 and 5 showed accre- 

 tion between 1965 and 1970; however, the rest of the northern area experi- 

 enced modest recession with rates less than 5 feet per year (Fig. 10, left). 

 The corresponding period for the southern locations shows similar results 

 (Fig. 10, right). These rates and trends are to be expected because this 

 period is one of rising lake level. The two sites where a significant 

 rate of accretion is indicated (sites 4 and 14) are adjacent to large dune 

 areas, indicating areas of sediment accumulation. It is unlikely that ris- 

 ing lake level would cause recession at these sites until near the peak in 

 the cycle. 



All sites showed general recession from 1967 to 1972. Rates were less 

 than 10 feet per year except at site 4 where there was severe erosion in 

 the spring of 1972 (Davis, Fingleton, and Pritchett 1975). The rapid in- 

 crease in lake level during this period is the primary cause for this gen- 

 eral erosion. 



49 



