Geology Reference
In-Depth Information
5.6.1. Aquifers
Because permafrost acts as an impermeable layer, groundwater movement is restricted to
taliks (see Figure 5.10). These may be of three types. First, a supra-permafrost talik may
exist immediately above the permafrost table but below the depth of seasonal frost. In
continuous permafrost, supra-permafrost taliks are rare, but in discontinuous permafrost
the depth of seasonal frost frequently fails to reach the top of permafrost since the latter
is often relict. In these areas, the supra-permafrost talik is a residual thaw layer (see Figure
7.10) which may be several meters or more thick. Second, intra-permafrost taliks are
unfrozen zones confi ned within permafrost. Third, sub-permafrost taliks refer to the
unfrozen zones beneath permafrost.
Taliks may be further distinguished by the mechanism responsible for their unfrozen
condition (Table 5.4). It is important to remember that taliks may be either cryotic (i.e.
below 0 °C) or non-cryotic (i.e. above 0 °C), or either open or closed depending upon
whether the talik reaches to the seasonally-thawed zone or not. Open taliks are common
even within continuous permafrost, the majority resulting from local heat sources such as
lakes, river channels, and other standing water bodies. Closed taliks usually result from
a change in the thermal regime of permafrost, such as might occur following lake drainage
and the downward aggradation of permafrost (as at Illisarvik; see pp. 92-94). Where
Table 5.4 .
The types of taliks that occur in permafrost regions.
Closed talik
a non-cryotic talik occupying a depression in the permafrost table below a lake or river (also
called “lake talik” and “river talik”): its temperature remains above 0 °C because of the heat
storage effect of the surface water.
Hydrochemical talik
a cryotic talik in which freezing is prevented by mineralized groundwater fl owing through
the talik.
Hydrothermal talik
a non-cryotic talik, the temperature of which is maintained above 0 °C by the heat supplied by
groundwater fl owing through the talik.
Isolated talik
a talik entirely surrounded by perennially-frozen ground; usually cryotic but may be non-cryotic
(see transient talik).
Lateral talik
a talik overlain and underlain by perennially-frozen ground; can be non-cryotic or cryotic.
Open talik
a talik that penetrates the permafrost competely, connecting suprapermafrost and subpermafrost
water (e.g., below large rivers and lakes). It may be non-cryotic (see hydrothermal talik) or
cryotic (see hydrochemical talik).
Thermal talik
a non-cryotic talik, temperature of which is above 0 °C due to the general thermal regime. It
includes the seasonally-thawed ground in the active layer.
Transient talik
a talik that is gradually being eliminated by freezing, e.g., the initially non-cryotic closed talik
below a small lake which, upon draining of the lake, is turned into a transient isolated talik by
permafrost aggradation
Source: Sloan and van Everdingen, 1988; van Everdingen (1990).
