QUANTITATIVE MORPHOLOGICAL COMPARISON OF THE CHARLEVOIX-ANTRIM AND NORTHPORT DRUMLIN FIELDS, MICHIGAN USING DIGITAL ELEVATION MODELS

The Charlevoix-Antrim and Northport drumlin fields, located in northwest Lower Michigan, are adjacent drumlin fields which are separated by Grand Traverse Bay. Morphological measurements were derived from 1:25,000 topographic maps and a 10m resolution Digital Elevation Model (DEM), combined with grain size analysis performed on collected drumlin sediments. Results from the morphological analysis show the two fields differ slightly in terms of length, height, and area. Drumlins in Charlevoix-Antrim field are 600 feet longer on average and larger in area by an average 51,400 square meters when compared to drumlins in the Leelanau field. The Charlevoix-Antrim and Leelanau fields displayed comparable results when examining the average numbers related to elongation (4.02 to 3.54) and azimuth direction (338 to 346). Comparisons of the statistical measurements and the distribution of drumlins, in response to sediment and bedrock types, have yielded the hypothesis the drumlins formed due to the erosion and deformation of pre-existing ground moraine during the retreat of the Two Rivers glacier. Thin ice thickness near the margin combined with high pore water pressures allowed for the drumlins to form concurrently during a period when the ice may have been stable or slowly retreating from the region. It is unlikely ice streaming was occurring during the time of formation, due to an average elongation ratio of 3.78. The elongation ratio may indicate the ground moraine displayed high shear strength where drumlins were formed; drumlins are more elongate where subglacial sediment has low shear strength. Drumlin shape varies from larger spindle and parabolic shapes in the center of the field to smaller elliptical shapes close to the margin. This has been attributed to variations in ice thickness, pore water pressure, and the amount of fracturing in the underlying bedrock. These drumlin fields are the youngest glacial landforms in the southern peninsula of Michigan.