USING GRAVITY METHODS TO DETERMINE THE EXISTENCE AND EXTENSION OF TUNNEL CHANNELS ACROSS THE UPPER PENINSULA OF MICHIGAN

A series of south-east trending kettle lakes dominate a large area of central Upper Penninsula, Michigan (UP). This area is located directly south of a large, branching network of tunnel channels found in the Lake Superior basin (Regis et al, 2003), and north of less robust channels in the Lake Michigan basin. At least two of these L. Superior channels outcrop on the UP, near Munising, MI. The goal of this study is to determine if the tunnel channel system continues across the UP connecting the L. Superior and Michigan channel networks. Using a gravimeter, the bedrock topography was mapped in 3 east-west tracts, perpendicular to the trend of tunnel channels, and south of the land-outcropping channels. The appearance of the kettle lake chain south of the L.Superior network inforced the location of the survey, due to the correlation between collapse features and buried tunnel channels (Clayton et al, 1999). The survey mapped the surface of the bedrock, and therefore located any bedrock erosion a tunnel channel would create. The existance of tunnel channels in the UP has important local implications for aquifer systems used by farmers, logging operations and residents. Tunnel channels also indicate specific drainage implications related to Laurentide ice sheet dynamics.