ORIGIN OF THE HIGH-RELIEF CHIPPEWA MORAINE, WESTERN CHIPPEWA COUNTY, WISCONSIN

The outermost Late Wisconsinan end moraine west of the Chippewa River, the Chippewa Moraine, has a relief of 50-60 m. The Perkinstown Moraine, the outermost Late Wisconsinan moraine east of the Chippewa River, has 3-10 m of relief. Cahow (1976) proposed that an interlobate zone enhanced sedimentation downflow from the 150-m-high Flambeau Ridge [FR] as ice was forced around the ridge. Ham and Attig (1996) proposed that a glacial surge formed the high-relief Chippewa Moraine. Our project evaluates mechanisms for the formation of the high-relief Chippewa Moraine.

Seven weeks of field mapping at a 1:24,000 scale near Jim Falls, WI, and detailed map/photo interpretation were employed to explore this phenomenon. The highest relief regions of the Chippewa Moraine are located SW of both FR and a Cambrian bedrock high in secs. 19 & 30, T31N, R7W, and largely coincide with the thickest glacial sediment (45-60+m, Lippelt, 1988). Striae on FR and streamlined topography in Taylor County indicate a southwesterly final ice-flow direction in the area. It seems unlikely that flow around FR formed two distinct lobes, as proposed by Cahow (1976). Rather, we propose that bedrock topographic highs caused compressive ice flow, enhanced erosion and supraglacial sediment production, and caused rapid ice stagnation on the lee sides of bedrock obstacles. The high-relief (15-30m) Chippewa Moraine extends into Rusk County where FR or another bedrock high was not present upflow. The sharp contact between the high- and low-relief moraine segments near the Chippewa River suggests that a surge of the Chippewa Lobe during the Late Chippewa Phase may have enhanced compressive ice flow along the entire western ice margin and produced thick accumulations of supraglacial sediment.

We propose the following glacial history: 1) S/SE flow and deposition of the low-relief Perkinstown Moraine in eastern Chippewa Co., 2) Change to SW ice-flow (and surge?) during the Late Chippewa Phase, and 3) Formation of the high-relief Chippewa Moraine where bedrock obstacles and/or rapidly slowing glacier ice enhanced sediment production.