FREEZE-THAW CYCLES

Commonly understood as the frequency of freezing and thawing, based on either air temperature or ground temperature, or simply the number of times the temperature crosses 0°C in a given time interval. Freeze-thaw cycles can range from long term (i.e. annual or longer) to short term (i.e. diurnal) in nature. The annual cycle is relatively easily characterised in terms of its time of occurrence, duration and intensity. Short-term freeze-thaw cycles are more difficult to characterise. According to the literature, the annual frequency of short-term cycles at the ground surface, however defined, is relatively low, rarely more than 50–100 in periglacial environments. These cycles are twice as numerous as air-temperature cycles and, with increasing depth, ground temperature cycles rapidly drop in frequency such that, below 10–20 cm in the soil, sediment or rock, only the annual cycles usually occur. Oceanic periglacial environments and mid-latitude alpine environments are commonly regarded as being the most suited for freeze-thaw processes affected by the diurnal cycle, but their low penetration into Earth materials, must cast doubt upon their effectiveness in frost weathering in these environments. The annual cycle and thermal stress are also important, and the complexities of frost weathering are still not fully understood.

[See alsocryosols, degree days, freezing index]