Submerged Wisconsin Sand Ridges Researchers from the Large Lakes
Observatory used the multibeam sonar mounted on the University
of Minnesota's research vessel, the Blue Heron, to investigate
submerged sand ridges off the Wisconsin shore of Lake Superior.
The surveyed area, depicted at right, is a 3.8 by 3.8 km area (2
by 2 nautical miles) with water depths between 13 and 32 meters.
Using the multibeam data, sediment samples and seismic
reflection data the researchers identified varying lake bottom
terranes. As seen on the images below, the near shore lake floor
is composed of glacial till with very little modern sediment
deposition, while off shore the lake floor consists of
lacustrine (lake) clays. In between the off shore clays and the
near shore tills are two different types of sand ridges. The
older ridges are several kilometers long, about half a kilometer
wide and rise approximately 3 to 6 meters above the lake floor.
These ridges are relict drowned shoreface-attached sand ridges
that formed when lake l