Frost-cracking and ice-wedge growth are fundamental processes within the permafrost environment. Extensive areas of contemporary permafrost terrain are characterised by frost-fissure polygons, formed by repeated thermal contraction-cracking of the ground. The incremental growth of ice veins and wedges along the axes of contraction-cracks contributes significantly to the volume of ground ice in near-surface permafrost. In areas beyond the present limit of permafrost, the recognition of ice-wedge pseudomorphs provides one of the few unambiguous indications of the former existence of permafrost conditions. An understanding of the processes of ice-wedge growth and thaw transformation is essential if contemporary ice wedges are to be used as analogues for Pleistocene frost-fissure structures, in palaeoenvironmental reconstructions.

The two main theories for the origin of the thick bodies of massive ground ice known to exist in the Western Canadian Arctic are (1) segregation‐injection and (2) buried glacier ice. Because buried glacier ice may contain significant quantities of stratified debris and may have experienced thawing and refreezing (regelation) on several occasions, it may be very difficult to distinguish between massive segregated ice and buried basal glacier ice. By use of cryostratigraphic and cryotextural (petrofabric) observations, massive ground ice bodies observed in the Sandhills Moraine, southern Banks Island, and the southern Eskimo Lakes region, Pleistocene Mackenzie Delta, are both interpreted as basal glacier ice. Other massive ground ice bodies which have been examined in the Western Canadian Arctic are best explained in terms of segregation‐injection.

The Sandhills Moraine is a Late Wisconsinan lateral moraine complex on southwest Banks Island. The occurrence of ice-ablation landforms, ground ice slumps, kettle lakes and catastrophic lake drainage in winter suggests the presence of substantial bodies of massive ground ice.The distinctive hummocky topography of the Sandhills Moraine is thought to reflect partial melt-out of this ice. Stratigraphic observations indicate that the ice is overlain irregularly and unconformably by glacigenic sediments, notably pebbly clay (till) and/or sandy gravels (outwash), while the ice itself possesses numerous and variable mineral inclusion3, faults and foliations. Petrofabric analyses indicate a strongly preferred orientation to the ice crystals. It is suggested that these characteristics are best explained if the ground ice is interpreted as relict glacier ice.

Massive ground ice, 5–6 m in thickness, is exposed within retrogressive thaw flow slides near Sabine Point, Yukon Territory. The ice is present near the upper surface of Buckland Till and is overlain and thaw truncated by mudflow sediments and a thick unit of peat and organic silt. Cryotextural and petrographic analyses suggest that the ice formed primarily by segregation processes. The ice occurs within an area of rolling terrain, surrounded by lacustrine basins. This may form a remnant of an initial post-Buckland surface, degraded by multiple cycles of thermokarst during the period 14 000 to 8000 years BP.

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