IDEAS ON THE ORIGIN OF THE SOUTHERN WISCONSIN KETTLE MORAINE--A HISTORICAL PERSPECTIVE

The Kettle Moraine (KM) of eastern Wisconsin extends from Walworth Co. northeastward to at least Manitowoc Co., a distance of approximately 200 kilometers. T. C. Chamberlin wrote extensively on the geology of the KM in the late 1800's (vols.1 & 2, Geology of Wisconsin: Madison, Wisconsin, Commissioners of Public Printing; vol.4 Transactions of the Wisconsin Academy of Sciences, Arts, and Letters). He used the word "kettle" in reference to an ice-block depression and apparently borrowed the term from residents of southeast Wisconsin who used "kettles", "pots and kettles", and "potash kettles" when referring to circular, bowl-shaped depressions (landforms) generally less than 150 m in diameter. Apparently, these landforms were named after the kettles commonly used at the time to boil down ash lye into potash cakes.

Chamberlin proposed that the KM consisted of two merged end moraines that formed along the eastern margin of the Green Bay Lobe and the western margin of the Lake Michigan Lobe. He also believed that the entire KM formed at one time. W.C. Alden conducted the first detailed geologic investigations of the southern part of the KM in the late 1800's and early 1900's (USGS Professional Papers 34 and 106). In contrast to Chamberlin's ideas, Alden mapped V-shaped moraines in the KM and suggested it formed progressively, from south to north, as the Green Bay and Lake Michigan Lobes wasted from their terminal positions. For reasons unclear, Alden later retracted his model, perhaps under the guiding influence of his mentor T.C. Chamberlin.

In recent years, we have re-mapped areas studied by Alden in Waukesha and Walworth Counties. Modern mapping and subsurface data support the early conclusions of Alden-namely that the southern KM formed progressively from south to north. We also find that much of the KM is a glaciofluvial feature formed of outwash heads, fans, and terraces (either collapsed or uncollapsed). Additionally, in the extreme southern part of the KM, the orientations of moraines indicate that the Lake Michigan Lobe began retreating from its terminal position while the Green Bay Lobe stayed at or near its late-glacial maximum. The geologic settings and glaciologic conditions of each lobe were significantly different and likely controlled this pattern of ice wastage and thus the formation of the Kettle Moraine.