Active layer

In environments containing permafrost, the active layer is the top layer of soil that thaws during the summer and freezes again during the autumn. In all climates, whether they contain permafrost or not, the temperature in the lower levels of the soil will remain more stable than that at the surface, where the influence of the ambient temperature is greatest. This means that, over many years, the influence of cooling in winter and heating in summer (in temperate climates) will decrease as depth increases.