Sea Ice Friction: The Effect of Ice Rubble

Abstract:

Ice deformation processes in the Arctic often generate ice rubble, and 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 fjord ice in Svea, Svalbard, which investigated the velocity and hold time dependence of sea ice friction involving ice gouge. Average air temperature for the duration of time in which experiments were run was -12.4°C, and the thickness of the level fjord ice was 70 cm. 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 moving a floating ice block through a channel of open water whilst subjected to normal loading, which was transferred through regions of ice rubble on both sides of the mobile block. The ice rubble regions were 30 cm deep and 50 cm wide. The displacement of the block and the force needed to move the block were measured. The rate dependence of friction was investigated for speeds of 10^-3 to 10^-2 ms^-1. To investigate the state dependence of friction, slide-hold-slide (SHS) tests were conducted for hold times ranging from 1 second to 18 hours. When comparing the results from these experiments with a model for ice friction presented by Schulson and Fortt (2013), similar behaviour is seen at low hold times, where the peak coefficient of friction has a linear relationship with the logarithm of hold time. This is not the case for long hold times, however, and we attribute this to thermal consolidation of the ice rubble region.