Physical modelling of gelifluction and frost creep: Some results of a large-scale laboratory experiment

An experimental slope was constructed in a 5 m × 5 m square refrigerated tank. The slope was formed of four sections, each consisting of regolith (soil) collected from a distinct bedrock lithology. The four lithologies utilized were granite, limestone, mudstone and slate. The slope was subjected to freezing and thawing from the surface downwards. Water was supplied at the base of the soil during freezing. Frost heaving and surface downslope soil movement were determined after each of 15 freezing cycles, and the profiles of soil movement with depth for each soil type were measured at the end of the 15th cycle. The experimental soils were non-cohesive; those derived from granite and limestone were respectively sandy and gravelly in texture, while those derived from mudstone and slate were silt-rich. Mass movement in the granite and limestone soils was due mainly to frost creep and was associated with the growth of needle ice. In the mudstone and slate soils, gelifluction was dominant as a result of high moisture contents caused by the melting of segregation ice. Mean per cycle rates of downslope soil transport for the granite, limestone, mudstone and slate soils were 5·8 cm³ cm^?1, 6·9 cm³ cm^?1, 21·2 cm³ cm^?1 and 31·2 cm³ cm^?1 respectively, units referring to the volume of soil passing a unit width of slope per cycle. Mass movement rates were shown to be strongly related to the silt content of the soils.