Some recent discoveries of ice-wedge cast networks in north-east Scotland

Ice wedges and ice-wedge polygons form as a consequence of soil contraction and cracking at winter temperatures below −15C to −20C (French 1976). Subsequent infilling by sediment results in their preservation as ice-wedge casts. Such casts, frequently used as palaeoclimatic indicators, have been widely recorded in Scotland, principally in the east (Galloway 1961; Sissons 1974), and mainly from exposures in gravel pits. There are few records of the associated ice-wedge polygon networks having been identified in Scotland. To date, networks have been recorded north of the border only in the Aberdeen area (Synge 1956, 1963; Clapperton and Sugden 1977) and in Berwickshire (Greig 1981). They are more abundant in England (e.g. Watson 1977), possibly as a consequence of the more prolonged permafrost conditions there allowing ground-ice cracks to extend and intersect to form polygons (Morgan 1972). The ice-wedge networks from NE Scotland noted here were, with the exception of Longside (Clapperton and Sugden 1977), discovered during a programme of oblique air photography being carried out by Aberdeen Archaeological Surveys with financial support from the Royal Commission on the Ancient and Historical Monuments of Scotland. Examination of the aerial photography taken in 1982 indicates the presence of ice-wedge cast networks at seven locations (Fig. 1). The dimensions of the polygons (Table 1) are broadly in accord with those of similar structures in present-day permafrost regions. Black (1974) notes that small polygons tend to develop in fine-textured soils, in areas where polygon development has continued for a long time, and where very . . .