Experimental simulation of ice-wedge casting: processes, products and palaeoenvironmental significance

Abstract

Abstract In six experiments, model ice wedges 150 mm high and ≤50 mm wide were thawed from the surface downward at 30 g in a geotechnical centrifuge, simulating ice-wedge casting during progressive active-layer deepening through permafrost. The frozen host soils ranged from sand to silt to clayey silt. Resulting ice-wedge pseudomorphs indicated that the degree of deformation during casting was determined by factors that control thaw consolidation. Hence, deformation increased as the host sediments became finer-grained and more ice-rich. Thaw of host sand at 15 and 20% gravimetric ice content and host silt at 20 and 40% ice content resulted in the formation of partially-developed ice-wedge pseudomorphs with an upper ‘plug’ of sediment derived largely from the cover soil, a central tunnel and a basal plug of sediment. Thaw of host clayey silt at 30 and 60% ice content resulted in the formation of fully developed pseudomorphs that were significantly narrower and shorter than the initial ice wedges. The experiments support the hypothesis that ice-wedge pseudomorphs tend to be better preserved in coarser-grained sediments that are not ice-rich and therefore deform little during thaw of constituent ice wedges. This selective preservation has probably led to underestimation of ice-wedge pseudomorphs in fine-grained soils that were originally ice-rich and therefore a bias towards reconstructing cold temperatures.