Frost bake

Frost baked is the name for a baked soil or soil structure that arises in fine-grained soils through the effects of frost . The bottom fermentation that occurs in summer is called shadow fermentation.

The ice crystals that form have two effects:

1. They drain the surrounding soil. With the drainage, the tension on the water phase increases, which is passed on to the soil particles via menisci , and thus leads to shrinkage and thus to a crumb or a segregated structure .
2. They widen the space in which they were created through frost elevation . When freezing, the volume of the water increases by 9%, so that fine, water-filled cracks and capillaries are widened ( frost burst ) and larger aggregates finally disintegrate into smaller units. The resulting structures are fine polyhedral structures, with stronger disintegration also frost splinter structures. The structures are often characterized by flat surfaces - in the case of subfloors of fine-grain substrates, plate structures are also created by the formation of flat ice lamellae.

The characteristics and stability of the frozen fermentation depend on the infiltration or sublimation of the soil water during the "freeze drying" of the soil. If a lot of water remains in the soil, the segregates are particularly unstable and disintegrate very quickly under the weight of the soil or when it rains. This must be taken into account when working the soil in spring.

When the frozen fermentation is formed, mixing processes also take place within the soil, which are known as cryoturbation . Ice lenses are created in the frozen ground by capillary replenishment of groundwater into the soil layer influenced by frost - in Germany up to a depth of 120 cm.

literature

• Karl Heinrich Hartge: Introduction to Soil Physics. Enke, Stuttgart 1978, ISBN 3-432-89681-6 , p. 90.