The active layer thickness is the maximum thaw depth over a period of two years.
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 (buildings, pipelines, roads, etc.).
These influences are mediated by the effects of the dynamics biological, pedologic, geomorphologic, biogeochemical, and hydrologic processes in permafrost.
In construction, the thaw depth is a major factor in ensuring the structural integrity of the objects in question.