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TitleOverflow generation for icing formation: A conceptual model
AuthorMorse, P D
Source2016 Yellowknife Geoscience Forum, abstract and summary volume; by Irwin, D; Gervais, S D; Terlaky, V; Northwest Territories Geological Survey, Yellowknife Geoscience Forum Abstracts Volume 2016, 2016 p. 48-49
Year2016
Alt SeriesEarth Sciences Sector, Contribution Series 20160259
PublisherNorthwest Territories Geological Survey (Yellowknife, Canada)
Meeting44th Annual Yellowknife Geoscience Forum; Yellowknife, NT; CA; November 15-17, 2016
Documentserial
Lang.English
Mediapaper
File formatpdf
Subjectswater table; ice; icing; aufeis; hydrostatic head; ice expansion; thermal contraction
ProgramLand-based Infrastructure, Climate Change Geoscience
LinksOnline - En ligne (complete volume - volume complet, PDF, 1.72 MB)
AbstractIcings (also aufeis, naled) form in winter by freezing of water that overflows across frozen surfaces (ground and/or ice). Icing development is most common in, but is not restricted to, permafrost regions. Source water may seep from the active layer, flow from a spring, emerge from a stream channel, or may be a combination of these inputs. Regardless of the water source, icings occur where lower boundary conditions of the source aquifer are confining, and where winter conditions are sufficient for the freezing front in the ground to contact the water table and also freeze any overflow. If the freezing front has reached the water table, water can move to unsaturated unfrozen zones for storage. When the frost table contacts the water table, the closed flow conditions initiate hydrostatic water level rise. If the hydrostatic level rises above the surface (ground or ice), an icing may develop. With continued downward freezing throughout the winter the water level rises gradually, but the level fluctuates rapidly with short-term air temperature change. Following a cold interval the level declines, but the subsequent rise in air temperature is followed by a rise in hydrostatic head, and the peak value is above the previous maximum level. Exfiltration (overflow), sometimes accompanied by vertical movement of the ground and ice, coincides with the hydrostatic level peak. The hydrostatic base value of each succeeding decline increases, as do peak values succeeding rises. Additionally, because of shallow overburdens, large fluctuations in water pressure can occur due to barometric loading, snowfall, icing in the adjacent stream, but may also be expected due to temperature expansion and contraction of overburden. Here, I suggest that as pressure changes are rapid and are related to air temperature fluctuations, the driving mechanism originates near the surface, and in a manner analogous to pressure changes observed in lake ice. Thermal contraction cracks that develop on the frozen surface of lakes during cold intervals infill with water from below that freezes in place and increases the mass of ice. Due to this increase, ice expansion during a warming interval is to a volume greater than the volume preceding contraction. This volumetric increase raises the internal pressure of the ice as the ice sheet is confined (not the water below). On large lakes this results in pressure ridges. Within closed-flow systems, small water volume changes induce large pressure variations. Thus I hypothesize that within closed-flow systems, infiltration of thermal contraction cracks in ice or frozen saturated ground by water from the unfrozen zone may reduce the hydrostatic head (water volume) during the cold interval. Subsequent expansion of frozen overburden with greater mass leads to an overall increase in volume and pressure of the upper boundary condition. When the pressure of the upper boundary increases, so must the pressure of the confined water, leading to exfiltration (i.e. icing) and/or surface uplift (and/or injection ice) where overburden is least resistant.
Summary(Plain Language Summary, not published)
Icings (also aufeis, naled) form in winter by freezing of groundwater that overflows across frozen surfaces (ground and/or ice). Icing development is most common in, but is not restricted to, permafrost regions. Overflow occurs when water pressure at depth fluctuates in relation to short-term high-amplitude changes in air temperature; however the mechanism physically linking this relation is unknown. Here a conceptual model is presented based upon a hypothesis that as pressure changes are rapid and are related to air temperature fluctuations, the driving mechanism originates near the surface, and in a manner analogous to pressure changes observed in lake ice.
GEOSCAN ID299416