деятельный слой(грунта Also known as annually thawed layer, depth of thaw, and depth to permafrost, this is the highly mobile layer of soil, subject to periodic thawing, located above the permafrost in tundra regions such as Spitzbergen or Alaska, and ranging in depth from a few centimetres to 3 m. answers.comAlexander Demidov); сезонно-протаивающий слой
активный слой(In environments containing permafrost, the active layer is the top layer of soil that thaws during the summer and freezes again during the autumn. • Permafrost is soil, rock or sediment that is frozen for more than two consecutive years. In areas not overlain by ice, it exists beneath a layer of soil, rock or sediment, which freezes and thaws annually and is called the "active layer"wikipedia.org)
answers.com Alexander Demidov); сезонно-протаивающий слой