Using LiDAR Data and ArcGIS to Evaluate Subtle Glacial Landforms Associated with the Early Chippewa and Emerald Phase Ice-Margin Positions, Barron County, Wisconsin

Glacial landforms in Barron County, Wisconsin, are a result of at least four glacial advances during the Pleistocene Epoch (2.58 to 0.012 Ma) (Johnson, 1986; Syverson and others, 2011). During the early Chippewa and Emerald Phases (Late Wisconsin Glaciation, 31-17 ka), till of the Pokegama Creek and Poskin Members of the Copper Falls Fm. were deposited over till of the River Falls Fm. (Illinoian Glaciation, >130 ka). These tills are all reddish-brown, sandy, and lithologically indistinguishable. Johnson (1986) was unable to map the location of the Emerald Phase ice margin using glacial geomorphology because these till surfaces do not display obvious glacial landforms in the field. Johnson used Late Wisconsin lake sediment in the northwestflowing Fourmile Creek valley as evidence for the Emerald Phase ice-margin position (Fig. 1). In addition, Fourmile Creek makes a 90-degree bend, and Johnson (1986) attributed this to flow along the Emerald Phase ice margin. LiDAR data obtained from the Barron County Land Information Office was used to evaluate the early Chippewa and Emerald Phase ice-margin positions proposed by Johnson (1986). High-resolution terrain models have been generated using the LiDAR data. The point spacing of the data is about 3 ft, and compared to ground truth points, the root mean square error (RMSE) of the survey is 0.29 ft. Even with LiDAR’s high resolution, primary glacial landforms are lacking on till surfaces in the 90 sq km study area. However, ArcMap’s 3D analyst tools and ArcScene’s 3D visualization capabilities reveal three distinct fluvial channels incised in the Poskin and Pokegama Creek till surfaces (Fig. 1). Longitudinal and cross-sectional profiles were generated to study channel morphology. These meltwater channels are sinuous, 900 to 1000 ft long, and reach maximum depths of 20 ft. They are different from modern channels because they cut across drainage divides, are sub-parallel to the land contour in some places, and typically appear abruptly on the landscape with little area for water catchment. Channel MC-1 (Figs. 1, 2) is an example of a lateral meltwater channel formed during deglaciation from the early Chippewa Phase ice maximum. Overall, these channels are evidence for a younger, less-modified landscape impacted by the Late Wisconsin Glaciation as compared to the River Falls Fm. till surface from the Illinoian Glaciation which lacks fresh glaciofluvial and glacial landforms. LiDAR data did not reveal a sharp landformassemblage difference between the Late Wisconsin and Illinoian till surfaces.