Geology Reference
In-Depth Information
closed taliks occur at depth in thick permafrost bodies, they probably refl ect long-past
fl uctuations in regional climate. In the discontinuous zone, where permafrost is often thin,
the unfrozen zones that perforate permafrost form “through” taliks linking unfrozen
ground above and below the permafrost layer.
5.6.2. Hydrochemistry
The low ground temperatures associated with permafrost regions means that reaction and
dissolution rates are reduced. At the same time, because of the increased solubility of
carbon dioxide at low temperature, the solubilities of calcites, dolomites, and gypsum are
increased.
The chemical composition of intra- and sub-permafrost waters will depend largely upon
the residence time in the subsurface, and the mineral composition of the aquifer. Low
dissolved solids are usually associated with rapidly moving groundwater, as might be found
in karst terrain or in fractured non-soluble rock. Sub-permafrost waters range from being
freshwater of the Ca(mg)-HCO
3
type, to saline, to calcium/sodium brines. Needless to
say, the latter may often be at temperatures below 0 °C, emerging from cryotic taliks. On
the other hand, in some places, such as Engineers Creek on the Dempster Highway,
northern Yukon, Canada, exceptionally iron-rich, sulfurous, and acidic springs occur, with
pH values as low as 2.8, temperature of
9 °C, and dissolved solids as high as 1080 mg/1
(Harris et al., 1983, pp. 75-79). In the same general vicinity, freshwater springs discharge
at a rate of 1.4 m
3
/s, with a temperature of
+
4 °C and a dissolved solids content of only
362 mg/1. Data such as these illustrate the importance of local geological conditions upon
the hydrochemistry and water quality of permafrost waters.
Intra-permafrost groundwater may be highly mineralized. For example, in central
Siberia, the mineralization of water in freezing taliks that still exist beneath previously
drained lakes may be as high as 60 g/l (Anisimova et al., 1973, p. 17). On the other hand,
certain perennial springs originating from sub-permafrost waters are known for their
excellent drinking quality. This is probably because of their low temperature and, in the
absence of CO
2
, the low solubility of carbonates in the host aquifer.
Perennial springs in areas of thick permafrost are relatively few but noteworthy. In
central Yakutia, perennial springs are regarded with almost religious signifi cance by local
Yakut residents. There, some springs have discharges that exceed 70 l/sec with dissolved
solids concentrations as high as 0.34 g/l (Anisimova et al., 1973). Those on Axel Heiberg
Island, Canadian High Arctic, are associated with gypsum and, being highly mineralized
(Na, Cl), give rise to a freezing-point depression of at least 7-10 °C. Spring discharge
temperatures range from
+
4.0 °C (Beschel, 1963; Pollard, 2005; Pollard and
McKay, 1997). Hot and/or highly mineralized springs are also known to occur in central
Alaska (Grantz et al., 1962) and in the Mackenzie Mountains of Northern Canada (e.g.
Takhini hot springs, southern Yukon Territory).
>+
5.0 °C to
<−
5.6.3. Groundwater Icings
Icings are sheet-like masses of ice which form at the surface in winter where water issues
forth from the ground (Carey, 1970). They are also known as aufeis (Washburn, 1979,
p. 44) or naledi (Brown, 1967b, pp. 74-79). Sometimes, the water source is of a sub- or
intra-permafrost nature, in which case the spring is usually a perennial one.
Maximum groundwater icing accretions involve sub- or intra-permafrost waters. They
usually occur in late winter when the ground is fully frozen and before the rise in air
