Geology Reference
In-Depth Information
Table 4 . 5.
Some typical rates of limestone solution under periglacial and non-periglacial
conditions.
Location
Mean Annual
Net Rate of Denudation
Total Carbonate
Precipitation (mm)
(mm/1000 years)
Hardness (ppm)
CaCO
3
MgCO
3
Arctic/Sub-arctic:
Hudson Bay, Canada
600
6.0
Somerset Island, Canada
130
2
84
22
Northern Yukon, Canada
215
n.d.
80
106
Svalbard
300
27
Tanana River, central Alaska
450
40
Svartisen, northern Norway
740-4000
400
Abisko, northern Sweden
800
5.3
Mountains:
Alps (mid-latitude)
2200
13
Equatorial
4000
32
Non-periglacial:
Western Ireland
1000-1250
51-63
66
11
Southern Algeria
60
6
Indonesia
200-300
83
Sources: Jennings (1971), Sweeting (1972, tables X and XI), Smith (1972), Thibaudeau et al. (1988),
André (2002).
solutional forms (karren) on exposed surfaces accelerate rock disintegration by other
weathering (frost) processes (see Dredge, 1992). A second relationship is characterized
by reticulate patterns of large “corridor” troughs. It is hypothesized that these were
created by meltwater erosion beneath weakly erosive glacier ice of the ice-cap interior. A
third relationship results from the hydrological conditions associated with warm-based
marginal ice, or from sustained thaw during the postglacial. This terrain occurs in the
sub-arctic zone of widespread discontinuous permafrost. Here, large fl uvio-karst systems
have formed, as in the Great Bear Lake region of the Mackenzie Valley region of northern
Canada (van Everdingen, 1981), and Akpatok Island in Eastern Canada (Lauriol and
Gray, 1990). The former is characterized by large closed depressions, powerful karst
springs, and ephemeral lakes, the latter by an extensive limestone plateau dissected by
dry valleys and large enclosed depressions or sink holes. In all probability, all these karst
systems pre-date the last glaciation and were either sustained beneath the
ice or re-established during the deglacial phase. The Nahanni karst, of the Mackenzie
Mountains, NWT, deserves special mention. This area is close to the southern limit of
widespread permafrost and lay beyond the limit of the Wisconsinan and Cordilleran ice
sheets. Here, the latest glaciation is thought to have occurred more than 300 000 years ago
(Brook and Ford, 1978, 1982). Thus, an extensive period of cold non-glacial conditions
has allowed the development of “the most accidented cold regions karst that is known”
(Ford, 1987, p. 520). It possesses impressive canyons, gorges, caves, springs, and subterra-
nean drainage.
Two models for karstifi cation (Figure 4.10) within the discontinuous permafrost zone
of northern Canada summarize the major relief features associated with cold-climate
