Physical modelling of bedrock brecciation by ice segregation in permafrost

The lower half of a large block of moist chalk was maintained at subzero temperatures while the upper half was cyclically frozen and thawed, simulating 19 seasonal temperature cycles in an active layer above permafrost. During the experiment, the rock surface heaved vertically by at least 34.7 mm. Sixty-one percent of the heave occurred during freezing periods, and is attributed primarily to ice segregation accompanying upward freezing from the permafrost table during the early stages of simulated winters. Thirty-nine percent of the heave occurred during thawing periods, and is attributed to ice segregation in the frozen rock beneath the thaw front during the mid to late stages of simulated summers. By the end of the experiment, the middle horizon of the chalk, representing the upper part of the simulated permafrost and the basal part of the active layer, had become strongly brecciated and rich in segregated ice. The style of brecciation has similarities with that in perennially-frozen limestone, sandstone and shale in Svalbard and Canada, and chalk frozen during Quaternary cold stages in France and England. These similarities suggest that ice segregation during perennial and seasonal freezing is an important process of weathering and coarse-sediment supply in areas of frost-susceptible bedrock. Copyright (C) 2001 John Wiley & Sons, Ltd.