Thaw depth Thaw depth In soil science, the thaw depth or thaw line is the instantaneous level down to which the soil has warmed to zero degrees celcius. The active layer thickness is the maximum thaw depth over a period of two years. The layer of soil over the thaw depth is called the active layer, while the soil below is called permafrost. The term frost front refers to the varying position of the thaw line during the periods of freezing/thawing. The knowledge of the thaw depth is important for the two major reasons: its influence on the ecology and on construction
Parent rock Parent rock Parent rock, also referred to as substratum, refers to the original rock from which something else was formed. It is mainly used in the context of soil formation where the parent rock (or parent material) normally has a large influence on the nature of the resulting soil. For example,clay soil is derived from shale while sandy soil comes from the weathering of sandstones. The term is also used in the context of metamorphic rocks where again the parent rock or protolith refers to the original rock before metamorphism takes place. Parent rocks can be sedimentary, igneous or metamorphic.