BROWN, Scott R., scbrown@geology.wisc.edu, and MICKELSON, D.M., Quaternary Research Group, Dept. of Geology and Geophysics, Univ. of Wisconsin, 1215 W. Dayton St., Madison, WI 53706; CLAYTON, Lee, Wisconsin Geological and Natural History Survey, 3817 Mineral Point Rd., Madison, WI 53705; and SCHNEIDER, Allen F., Department of Geology, Univ. of Wisconsin-Parkside, Kenosha, WI 53141.

SUBGLACIALLY ERODED LANDFORMS ON THE DOOR PENINSULA, WISCONSIN, USA

Asymmetrical dolomite hills, about 50 feet high and a quarter-mile across, are located along a Silurian escarpment in Door County, Wisconsin. They are characterized by a prominent, steep rise on the northern (up-glacier) side of the hill and a gentler slope on the southern side. Glacially striated planar bedrock surfaces commonly occur both at the base of the hill and at its crest. Some of these hills have small channels running from the base of the up-glacier slope along the eastern and western margins. Similar hills appear to be present along the Niagara escarpment on Bruce Peninsula, Ontario, based on topographic map interpretation.

Possible formation mechanisms include wave action cutting a bench and cliff along the northern slope, or preglacial differential erosion of stratigraphic units. Beach sediments are not present at the base of most of the hills, however, and the presence of glacial striations seems to discount a mechanism solely by preglacial erosion. More likely the hills were formed by glacial erosion near the ice margin or erosion by subglacial or ice-marginal water. The orientation of these hills appears to be controlled by the direction of ice movement (from the north) as indicated by striations and drumlins in the area. The presence of channels surrounding these forms suggests that the hills have been at least modified by flowing water. We suggest that the hills were formed primarily by subglacial water, however the thickness of the water layer and the duration of the flow beneath the ice are not clear.