The effect of ice rubble on ice-ice sliding

Ice deformation processes in the Arctic can generate ice rubble. Many situations arise where ice fragments of varying size separate sea ice floes. While the shear forces between sea ice floes in direct contact with each other are controlled by ice-ice friction, what is not known is how the slip of the floes is affected by the presence of rubble between the sliding surfaces. We present the result of field experiments undertaken on sea ice in the Barents Sea. A double-direct-shear experiment was done on floating sea ice in the field, with the addition of rubble ice between the sliding surfaces. This was achieved by pulling a floating ice block through a cut channel of open water 3m long, where broken ice filled the gap between the block and the channel sides. The displacement of the block and the force needed to move the block were measured. The time that the block was held motionless to allow the rubble to consolidate was recorded - this ranged from seconds to several hours. We found that the 'hold time' controls the maximum force needed to move the block. The relation between hold time and force is highly non-linear from which we deduce thermal consolidation is the controlling mechanism.