Abstract
The shape of air bubbles and air bubble behaviours in natural ice may provide a greater understanding of ice dynamics. Micro-computed tomography (MicroCT) and optically imaged data collected from samples from the lateral shear margin of the Priestley Glacier show the variation of bubble shape. These bubbles are less stretched than we would expect for the amount of shear. This poses the question of what controls the kinetics of bubble shapes. How do deformation conditions (e.g., temperature, strain rate) affect the balance between bubble deformation (stretching the bubbles) and restoration to a sphere, driven by surface energy. We are investigating this using a deformation experiment that allows for the removal of the ice sample to take photos of the bubbles and the return of the sample for more deformation after this. The photos taken at regular time intervals dring deformation allow us to better understand the process es and changes occurring during deformation. In preliminary experiments the sample had been cut at 45 to the c-axis maximum, to mimic the deformation in the field, and removed for imaging every 23-26 hours. The sample was put under ~0.55MPa of stress at ~-11 C. The experiment run time was 172 hours, achieving a total axial strain of 0.18 at strain rates of 3x10-7s-1 (10a-1). The bulk strain and the strain calculated from bubble shape change are very similar, suggesting that at these fast rates bubble deformation is much faster than restoration. Experiments at slower rates are needed to scale back to natural conditions.