The types and formation of taliks in the permafrost zone

Even in the most severe climatic conditions the spatial distribution of permafrost is not universally continuous. Within the permafrost zone the frozen ground can be absent within many sections of river valleys and watersheds, on south-facing slopes, under lakes, at sites of concentrated discharge of groundwater or of its recharge by seepage, volcanic craters, calderas, under some of the present glaciers and above the interior-Earth thermal anomalies associated with oxidation reactions, etc.

Within the region of distribution of continuous permafrost, unfrozen ground occupying small areas and existing continuously for more than a year is termed a talik. When the area of unfrozen ground appears to be comparable with or larger than the area of frozen ground the unfrozen ground is termed a talik zone or massif of unfrozen ground. According to the relation of taliks and talik zones to the surrounding frozen ground, they can be divided into open (penetrating through the whole frozen stratum) and closed (sometimes they are termed ‘pseudotaliks’), penetrating into the frozen stratum to some depth and underlain by permafrost. Often thawed and unfrozen layers, lenses, channels and bodies of other form, bordered at the top, bottom and sides by permafrost are found in geological sections of the permafrost zone. Such formations are termed inter- and intrapermafrost taliks in the literature.

Strictly speaking, in addition to taliks proper (frozen earlier, but thawed now), the so-called original taliks, represented by ground not frozen before and existing in the unfrozen state, can be found in nature.