The effect of hydrostatic pressure on crack formation in ice single crystals

Many tiny cracks are observed near the surface of deep ice cores drilled from polar ice sheets. These cracks probably form during the ice core drilling process at hydrostatic pressure, which increases linearly with depth. We studied crack formation in ice experimentally by deforming ice single crystals using a uniaxial compression apparatus with controlled hydrostatic pressure. The uniaxial compressive stress was applied to ice samples under a hydrostatic pressure of 20 MPa at -18℃. A constant strain rate was set at ~10^-7s^-1. The c-axis orientations of the ice single crystals were parallel to the compression axis. The compression test results show that cracks formed in ice samples at a stress level of over 15MPa after 0.5% compressive strain, except for samples that deformed non-uniformly. These cracks grew along basal and parallel planes to the c-axis. This result suggests that the tiny cracks at the surface of ice cores could originate in local high stress just under the tip of the cutter.