Degradation by freeze-thaw cycles
Introduction
Frost weathering is a mechanical weathering process induced by stresses created by the freezing of water into ice within rocks. It encompasses volumetric expansion, where water in cracks, pores, joints, or bedding planes freezes and expands to exert pressure that fractures the rock, also known as frost wedging or ice wedging, and ice segregation, where ice lenses grow by attracting unfrozen water from surrounding pores.[1][2][3] This physical disintegration occurs without altering the rock's chemical composition, distinguishing it from chemical weathering processes.[1]
The process often begins with the infiltration of liquid water into preexisting weaknesses in the rock, such as microcracks or fissures, facilitated by precipitation or melting snow.[1] In the case of volumetric expansion, upon freezing, water expands by approximately 9%, generating internal pressures that can reach 20 MPa or more, sufficient to propagate cracks and dislodge fragments from the parent rock.[4][5] Repeated cycles of freezing and thawing—typically driven by diurnal or seasonal temperature fluctuations around the freezing point—gradually enlarge these fractures, leading to the breakdown of bedrock into smaller particles over time.[1] The efficiency of this process depends on factors like rock porosity, permeability, and the availability of water, with finer-grained rocks often more susceptible due to their higher water retention.[6]
Frost weathering is most prevalent in cold, temperate, and periglacial environments where freeze-thaw cycles are frequent, such as high latitudes, alpine regions, and areas influenced by permafrost.[2] Notable examples include the formation of hoodoos in Bryce Canyon National Park, where differential weathering creates towering rock spires, and the talus slopes at the base of mountain fronts in unglaciated terrains.[4] In these settings, the process can operate on various scales, from microscopic crack propagation in individual boulders to landscape-scale disintegration of cliff faces.[7]
In geomorphology, frost weathering plays a critical role in sediment production and landscape evolution, particularly during glacial and periglacial periods, by accelerating the breakdown of bedrock into transportable regolith.[8] Studies indicate that during the Last Glacial Maximum, frost-driven processes more than doubled erosion rates in unglaciated regions, such as the Oregon Coast Range, from modern rates of 0.08 mm/year to approximately 0.2 mm/year.[8] This enhanced weathering contributes to soil formation, slope instability, and the development of features like scree fields and patterned ground, influencing broader Earth surface dynamics in cold climates.[9]