DETAILED SUFICIAL GEOLOGIC MAPPING AND TERRAIN ANALYSIS OF THE BLUE HILLS FELSENMEER VALLEY, RUSK COUNTY, WISCONSIN

The Paleoproterozoic Barron Quartzite of west-central Wisconsin forms a rolling upland with as much as 180 meters of relief known locally as the Blue Hills. Our study concerns the Blue Hills Felsenmeer State Natural Area in Rusk County, which encompasses a small valley 300 meters long, 100 meters wide, with 25 meters of relief. Underlain by angular quartzite boulders averaging 30 cm long, the valley contains little to no vegetation and contrasts markedly with the surrounding mixed conifer and hardwood forest. Previous studies described the boulder accumulation in this valley as a felsenmeer, which requires in situ frost weathering in a periglacial environment. This work is part of a larger study re-examining the origin of this valley in effort to evaluate if the feature is truly a felsenmeer (rocks frost-shattered in place), and determine if other mechanisms, such as talus accumulation, may account for this feature (Thompson and Syverson, 2006).

We present a detailed surficial geologic map of the valley generated through collection of differential GPS data in the field and supplemented by aerial photo interpretation. The map is plotted on a LiDAR (Light Detection and Ranging) base with a two-foot contour interval provided by courtesy of the Barron County Soil and Water Conservation Office. Mapping targets include areas of boulder accumulation with no vegetation, areas of boulder accumulation with some vegetation, bedrock outcrops, and possible meltwater features.

LiDAR data were also employed to generate digital elevation models, which can be used to create shaded-relief maps and conduct terrain analysis. Parameters obtained from digital terrain analysis—including slope angle and aspect angle—may provide additional insight regarding the mechanism of landscape development by comparing locations of boulder accumulation with slope angle and aspect values using GIS. Areas of boulder accumulation with slopes near the angle of repose would be more suggestive of talus than felsenmeer origin, while areas of boulder accumulation with low slopes may be more suggestive of a felsenmeer origin.