Rapid Healing of Thermal Cracks in Ice

The structural integrity of the arctic sea ice cover is under threat owing largely to the combination of thinning and larger waves. Another contributor may be thermal cracking. In concentrating stress, thermal cracks may weaken the cover. Of interest, therefore, is the strength of thermally damaged ice. To that end, new experiments were performed on sea ice and on lab-grown saline and salt-free ice that had been cracked by thermal shocking. As expected, the cracks weakened the materials in accord with fracture mechanics. However, within tens to hundreds of seconds of shocking, the strength recovered completely, for the ice had healed. Healing is attributed to thermally activated sintering related to surface diffusion, assisted possibly by the formation of a quasi-liquid layer on crack faces. Whether behavior on the small scale is indicative of behavior on the large scale remains to be determined.