PERIGLACIAL LANDFORMS | Ice Wedges and Ice Wedge Casts

Abstract

Ice wedges are steeply to vertically laminated bodies of ice that form by repeated infilling of thermal contraction cracks in permafrost. Soil wedges form where the cracks fill with soil, and composite wedges form where they fill with mixtures of soil and ice. The size and shape of wedges, and the relative age of the wedge infill and host material depend on the interactions between thermal contraction cracking and ground-surface stability. Thaw of ice veins and wedges sometimes results in secondary infilling of the space left by melting ice, the infilling mechanisms being determined by thaw consolidation, tunnel collapse, and groundwater movement. The resulting ice-wedge pseudomorphs or casts are common in terrestrial cold-climate sediment sequences and indicate the former occurrence of permafrost. The paleoenvironmental significance of small, relict veins and wedges is often difficult to pinpoint because thermal contraction cracking occurs frequently in areas of continuous permafrost, rarely or locally in discontinuous permafrost, and occasionally in seasonally frozen ground.