| Title | Overflow generation for icing formation: A conceptual model |
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| Author | Morse, P D |
| Source | 2016 Yellowknife Geoscience Forum, abstract and summary volume; by Irwin, D; Gervais, S D; Terlaky, V; Northwest Territories Geological Survey, Yellowknife Geoscience Forum Abstract and Summary Volume
2016, 2016 p. 48-49  Open Access |
| Links | Online - En ligne (complete volume - volume complet, PDF, 1.72 MB)
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| Image |  |
| Year | 2016 |
| Alt Series | Earth Sciences Sector, Contribution Series 20160259 |
| Publisher | Northwest Territories Geological Survey (Yellowknife, Canada) |
| Meeting | 44th Annual Yellowknife Geoscience Forum; Yellowknife, NT; CA; November 15-17, 2016 |
| Document | serial |
| Lang. | English |
| Media | paper |
| File format | pdf |
| Subjects | Nature and Environment; water table; ice |
| Program | Climate Change Geoscience Land-based Infrastructure |
| Released | 2016 01 01 |
| Abstract | Icings (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 ID | 299416 |
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