Geology Reference
In-Depth Information
fi rst approximation, lakes with minimum widths of twice the permafrost thickness will
always be underlain by through-going taliks, and most lakes
>
2.0 m deep will possess some
sort of talik.
Numerical models are limited by their inability to predict disequilibrium permafrost
conditions. The downward penetration of a thermal wave is such that a lag may develop
with respect to surface temperature. One estimate is that, with a mean surface tempera-
ture of
10 °C, a thaw period of 10 000-20 000 years is required to form a through-going
talik in a permafrost body 500 m thick (Mackay, 1979a, p. 30).
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5.3.2. The Illisarvik Drained-Lake Experiment
The ideal way to investigate the growth of permafrost is via a three-dimensional conduc-
tive-convective heat transfer approach. However, this is not easy to model and fi eld data
are not available. This was why a novel and multidisciplinary fi eld experiment on the
growth of permafrost was initiated in August 1978 in the Western Canadian Arctic by
J. R. Mackay (1981b, 1997). The site is termed Illisarvik (Inuit: “the place of learning”).
Essentially, the experiment involved the artifi cial drainage of a shallow tundra lake (Figure
5.4). A bowl-shaped talik (unfrozen basin) with a maximum depth of 32 m underlay the
lake bottom prior to drainage. Following drainage, the growth of permafrost has been
Figure 5.4.
Oblique air photograph taken of drained Lake Illisarvik, August 1979, one year after
lake drainage. Two shallow ponds remain, the larger of which (nearer the outlet) is underlain by a
talik. The plunge pool, eroded to a depth of 3 m on August 13, 1978, is on the seaward side of the
outlet. Several survey grid lines are visible on the drained lake bottom. The photo is supplied cour-
tesy of Professor J. R. Mackay.
