Microstructural change in ice: III. Observations from an iceberg impact zone

During a full-scale iceberg-impact study conducted in July 1995 on the Labrador coast, Canada, a sample of ice was retrieved from the impacted surface of an iceberg. The sample was thin-sectioned and the observations of the contact-zone microstructure are presented in this paper. Thin sections were prepared from two slabs cut parallel to the impacted surface. In each of the thin sections taken from the impacted-surface slab, fine-grained material was found to surround parent-size grains (as observed in the second slab). A boundary between the parent grains and the grains of modified microstructure was found running approximately parallel to the impacted surface in each of the thin sections taken from the impacted-surface slab. This boundary was pronounced towards the edges of the contact zone. Lateral movement of grains outward along this boundary was observed in thin sections near the edges but not near the centre of the contact zone. The thin sections were compared to the results of medium-scale indentation tests in 1989 and 1990 from the Arctic Ocean. The same type of fine-grained material and layer formation of modified microstructure was found in the contact zones.