Measurement, correlation, and mapping of Glacial Lake Algonquin shorelines in northern Michigan

Glacial Lake Algonquin, the most widespread proglacial lake in the Great Lakes basin, attained a high (Main) stage at about 11,000 B.P., at which time it developed a conspicuous shoreline. Several lower, less obvious Algonquin shorelines also exist. Previous research on this lake has involved three drawbacks: (1) imprecise methods of establishing the location and elevation of shoreline features, (2) misidentification of some offshore coastal landforms as beach ridges, and (3) tenuous and difficult correlation of named shorelines across wide distances. We believe that more than one name is used for some lake phases, making correlation difficult. Our study focused on these problems by surveying and mapping 160 Algonquin wave-cut bluffs throughout northern Michigan. We utilized global positioning system (GPS) technology to precisely record the three-dimensional positions of the bases of these bluffs and statistically fit trend surfaces to these positions. Classification of bluff data indicates that four strong Algonquin shorelines exist in the region, for which we recommend these names: Main, Ardtrea, Wyebridge, and Payette. Weak evidence for a possible fifth, lower shoreline was observed at five locations. Maps of the landscape during each lake phase were created, revealing islands not previously recognized. Rebound curves and maps of the lake during each phase, using the positional data set, indicate that isostatic rebound in the study area appears to be greatest in the northeast sector.