Geology of the Ice Age National Scenic Trail

Northern Kettle Moraine Ice Age Trail Segments

T he northern kettle moraine segments of the IAT are located in eastern Wisconsin (fig. 3). The Kettle Moraine really isn’t a moraine at all by most definitions. Its hills are composed mostly of stream-deposited sand and gravel instead of mostly till (SB 5) like other moraines. But it is a geographic feature that has had this name for over a hundred years and will continue to be called the Kettle Moraine for years to come! It formed between the Lake Michigan and Green Bay lobes over a period of several thousand years as the glacier retreated from its maximum extent position (fig. 1). It contains various landforms, including eskers (SB 13), hummocky sand and gravel (SB 11), moulin kames (SB 12), and kettles (SB9). Individual landforms are detailed in the trailsegment descriptions. In some places it is a single ridge and in others it bifurcates, leaving one ridge on the Lake Michigan Lobe side and another on the Green Bay Lobe side, with a low area in between. To the west and east of the Kettle Moraine, drumlins show the ice- flow direction (fig. 90). Although there are only four trail segments in the northern Kettle Moraine, they total more than 30 miles in length and exhibit spectacular glacial features. Because much of the surrounding area is state forest, much of the trail is on public land. Numerous other trails and the Henry S. Reuss Ice Age Visitor Center near Dundee offer great opportunities for recreation and learning. The easternmost segment of the IAT is La Budde Creek. It follows a glacial drainageway along the Lake Michigan Lobe edge of the Kettle Moraine. The Greenbush Segment (fig. 90) winds mostly through high-relief hummocky topography (SB 11) on the Green Bay Lobe side of the Kettle Moraine. The southernmost half-mile crosses open land that is pitted outwash (SB 10) deposited when all but isolated masses of buried ice had disappeared from the low, and now central, Kettle Moraine area. 114 Northern Kettle Moraine Ice Age Trail Segments Northern Kettle Moraine Ice Age Trail Segments 115 The Parnell Segment crosses more pitted outwash and some till surface before climbing into the Lake Michigan side of the Kettle Moraine about a half mile before the junction with the Parnell Tower trail. The remainder of this segment and the Milwaukee River Segment are in the Lake Michigan Lobe side of the Kettle Moraine. The northern Kettle Moraine is mostly a double ridge, and the central and southern Kettle Moraine is mostly a single broad ridge. Figure 91 shows cross sections that illustrate Figure 90. Shaded relief of the northern Kettle Moraine IAT segments (red): (12) La Budde Creek, (13) Greenbush, (14) Parnell, (15) Milwaukee River Segment in Fond du Lac County. Green Bay Lobe (western) and Lake Michigan Lobe (eastern) sides of the Kettle Moraine and meltwater channel are shown with black arrows. Blue arrows show ice-flow direction. The letter d on the right indicates Lake Michigan Lobe drumlins. The letters d on the left indicate Green Bay Lobe drumlins. The Campbellsport Drumlins Unit of the Ice Age National Scientific Reserve (16) is in the middle group of Green Bay Lobe drumlins. Note that at this scale the individual drumlins appear to cluster in bands perpendicular to ice flow. Yellow lines and numbers indicate highways. Cities shown (yellow): (C) Campbellsport, (D) Dundee, (G) Greenbush, (K) Kewaskum. VC refers to the Henry S. Reuss Ice Age Visitor Center. (Base map constructed from USGS National Elevation Dataset and modified by WGNHS.) 116 Northern Kettle Moraine Ice Age Trail Segments how we believe the northern Kettle Moraine formed. Throughout the period of glaciation this was a low area on the ice surface (fig. 91a). Meltwater from both lobes drained into this low trough and then southwestward toward Walworth County. Sand and gravel accumulated on this riverbed on the ice surface. Eventually the sand and gravel was thick enough that it insulated the ice below. Off to either side, where clean ice or ice with a very thin debris layer could absorb more radiation from the sun, melting was more rapid. Eventually two troughs formed, with the ridge of debris-covered ice between them (figs. 91b, 91c). As these Figure 91. Three-dimensional diagrams of probable sequence in the formation of the double ridge of the northern Kettle Moraine: (a) as ice begins to thin, meltwater...