A RE-EVALUATION OF THE KELLY’S ISLAND GROOVES, LAKE ERIE, OHIO

Kelly’s Island, a small island that straddles the western and central basins of Lake Erie contains perhaps the most spectacular example of glacial “grooves” in the world. The site contains linear ridges and depressions in a U-shaped channel that is ~100m long and 10m wide. Individual ridges ornament both the base of the channel and the near-vertical channel walls. They are up to 20m long, and as short as a few centimeters long. These “grooves” have received little attention in the glacial literature but a few researchers have indicated that they are the product of direct erosion by glacial ice or by squeezing of sediment below the ice. This paper presents a re-evaluation of the “grooves” and contests that these were not formed by glacial ice but rather by pressurized subglacial water. Several observations support this interpretation. First, the larger remnant ridges prominent at the site contain hairpin-shaped scours that are wrapped around the upflow facing noses of the ridges. These are common features that have been interpreted to have formed by vortices in meltwater flows. More specifically, these scours occur in parallel sets containing up to 5 scours. Typically, the most prominent scour is at the upflow end of the ridge, and the shallowest and least prominent scour is downflow. These are interpreted to have formed by migrating vortices that may have been controlled by the bedrock topography, or by a protrusion at the base of the ice. In addition to the scours a prominent vertical plunge feature contains long (several meters), but narrow (a few centimeters) “grooves” that cross-cut each other as the vertical sculpture becomes horizontal. These features are typical of those noted in highly turbulent, high velocity flow in modern environments. Finally, several single narrow linear channels cross-cut the main field of grooves at angles of up to 45 degrees. These channels are morphologically similar to the other grooves at the site, but they obviously represent a late-stage erosion event. It is difficult to envisage ice scouring individual channels of only a few tens of centimeters wide but tens of meters long while leaving the surrounding grooves untouched.