Cryosphere: The portions of the Earth (in the atmosphere, at the surface, in the ground) in which water is in solid form. It includes snow and ice crystals in the air, snow cover and ice caps, floating ice (on rivers, lakes, oceans), glaciers, permafrost, etc. The word is derived from the Greek "kyros," meaning frost or icy cold.
Intergelisol: A sub-surface layer of frozen ground that might persist for a few years but is not permanently frozen ground and is not considered to be permafrost (soil and rock whose temperature is permanently at or below 32 degrees).
Mollisol: In regions of permanently frozen underlying soil, mollisol is the surface layer that freezes in the winter and thaws in the summer. It varies in thickness from a few inches to several feet.
Pereletok: A sub-surface layer of frozen ground that might persist for a few years, but is not permanently frozen and is not considered to be permafrost. The term is Russian, meaning "survives over the summer."
Permafrost: Permanently frozen ground; it underlies about 85 percent of the state of Alaska, and in northern Alaska it reaches its greatest thickness, about 2,000 feet.
Subgelisol: Unfrozen ground beneath permafrost.
Talik: Permanently unfrozen ground in regions of permafrost.
