Using axe to test ice thickness at lower end of Hotcake Slough Knut Kielland uses an axe to test the thickness of the ice at lower end of Hotcake Slough. Process Observed: Open Water (Hidden)Ice ThicknessIce Strength Date Process Observed: Saturday, March 31, 2012 Galleries: Main part of the Tanana River at lower end of Hotcake Slough Gallery