Kehew, A.E., Ewald, S.K., Esch, J.M., Kozlowski, A.L., 2013. On the Origin of Tunnel Valleys of the Saginaw Lobe of the Laurentide Ice Sheet; Michigan, USA. Boreas 42, 442-462. doi:10.1111/j.1502-3885.2012.00295.x