A GIS APPROACH TO SEDIMENT MASS BALANCE IN TUNNEL CHANNEL SYSTEMS, LAKE SUPERIOR BASIN AND THE UPPER PENINSULA OF MICHIGAN

Tunnel channels are ice-marginal features of ice lobes of ice sheets, including the Laurentide Ice Sheet in North America. They discharge water from the base of the ice in large, episodic events. Sediment removed from at least the tunnel floor, creates the erosional form we observe, and is deposited in front of the glacial margin where conditions are suitable for it to accumulate. The classic landform assemblage includes a broad channel that rises to the ice sheet margin (moraine) that in some cases contains an esker, both of which lead to a break in the moraine, where deposition begins (Clayton et al., 1999).

A network of anastomosing tunnels preserved in the sandstone floor of the eastern Lake Superior basin (Patterson et al., 2003; Regis et al., 2003; Derouin, 2008) average 5 km in width and reach different depths of incision. Some are over 200 m deep and over 100 km long. Directly south of the Lake Superior tunnel channels, the eastern Upper Peninsula of Michigan, a narrow land mass between Great Lakes basins, is dominated by large fan deposits and a moraine-complex comprised of overlapping fan heads (Blewett and Winters, 1987; Derouin, 2008). The goal of this study was to compare the amount of material (in metric tons) missing from the channels to that deposited in the fans using GIS analysis of the digital elevation models based on SRTM elevation data for the surface, NOAA data for the lake floor and interpolation of available well logs for the subsurface. The mass of the fans was calculated assuming that all sand deposited above the bedrock surface originated from tunnel discharge. The mass of tunnel channels were calculated assuming an initially flat lake floor, and subtracting the material from the channels incised into the sandstone.

The fans contain over 7 x 10¹⁰ Metric tons of mainly sand, while the tunnel channel incision through sandstone removed over 1 x 10¹² Metric tons of material from the bedrock basin. This suggests that two orders of magnitude of sediment was transported away from the Upper Peninsula, potentially deposited in Lake Michigan, Lake Huron, and the Lower Peninsula of Michigan. We suggest potential areas of sediment accumulation include the sand on the northwest shore of the Lower Peninsula of Michigan (e.g. Sleeping Bear Dunes)and partially-filled tunnel channels in on the Lake Michigan floor.