USING HIGH RESOLUTION LIDAR-DERIVED DEM’S TO INTERPRET EARLY HOLOCENE DUNES AND THEIR REACTIVATION AROUND 4000 YRS AGO, NORTHWEST WISCONSIN

Eolian dunes are prevalent in the sand barrens of Burnett County in northwest Wisconsin. These formed after the abandonment of an aggradational surface formed by meltwater from the Superior Lobe of the Laurentide Ice Sheet in the St Croix River valley and the earlier infilling of glacial Lake Grantsburg. In contrast to the relatively high relief of the dunes, the surrounding low relief barrens are primarily covered in organic sediments and wetlands.

The dunes have up to 20 m of local relief and are dominantly transverse and barchanoid ridges formed from NW winds. A recently acquired 1.5 m LiDAR-derived high-resolution digital elevation model (DEM) aided in the detection of blowouts and lower relief (up to 3 m) parabolic forms on the larger dunes. These smaller forms, which were not detectable with traditional topographic maps and coarser 10 m DEM’s, were formed by southerly winds. Aided by the high resolution DEM’s, we collected samples from the relatively high-relief dunes and superimposed smaller parabolic forms for OSL dating to test if they formed contemporaneously. Samples were collected between 1.35-1.5 meters depth in order to estimate the time of stabilization and avoid partial bleaching from pedoturbation.

Preliminary results indicate the higher relief dunes stabilized between 9-10 ka (n=5), consistent with dune records from other locations in northern Wisconsin. Two samples collected from the lower relief parabolic forms indicate they stabilized at ~ 4 ka. Future work will target dating these smaller blowouts and superimposed dune forms that are evident on the 1.5 m DEM across the sand barrens to determine if the dunes in the region record evidence of the proposed midcontinent centennial-scale drought at 4.2 ka. In addition, these DEM’s have the potential to greatly improve site selection in eolian landscapes with low relief, especially in forested landscapes like the Upper Midwest.