Soil Cryogenic Structures and Their Implications for Land Use in Alaska

摘要

Cryogenic structure (patterns made by ice inclusions) in seasonally frozen and permafrost— affected soils result from ice formation during freezing. Analysis of cryogenic structures in soils is essential to our understanding of the cryogenic processes in soils and to formulating land use management interpretations. When soils freeze, the freezing front moves downward and attracts water moving upward resulting in mainly horizontal lenticular ice formation. Platy and lenticular soil structures form between ice lenses in upper active layer. The reticular soil structure usually forms above the permafrost table caused by freeze— back of the permafrost. The upward freeze— back resulted in platy soil structure and the volume changes following the annual freeze — thaw cycle resulted in vertical cracks. The combined result is an ice — net formation with mineral soils embedded in the ice net. The upper permafrost layer that used to be a part of the active layer has an ice content exceeding 50% due to repeated freeze — thaw cycles over time. The mineral soils appear in blocks embedded in an ice matrix. The permafrost layer that never experienced the freeze— thaw cycle often consists of alternate layers of thin ice lens and frozen soils with extreme hard consistence and has relatively lower ice content than the ice — rich layer of the upper permafrost. Ice contents and thaw settling potentials associated with each cryogenic structure should be considered in engineering and land use interpretations.