Geology Reference
In-Depth Information
Table 8.2 . Some examples of the effects of human-induced vegetational changes upon
permafrost conditions in central Siberia, according to P. I. Koloskov (1925).
(A) Increase in average July soil temperature at 40 cm depth after ploughing, Yenesie region
Soil
Previous Vegetation Cover
Temperature Increase (°C)
Semi-bog
Forest
+
14
Peat-bog
Grass
+
12
Semi-bog
Grass
+
9
Light sod, gravelly
Grass
+
3
(B) Soil temperature changes as a result of deforestation, Amur Province
Depth of Measurement
Thickness of Snow
Soil Temperature Changes
(m)
(cm)
within one Year (°C)
0.2
20
+
0.5
10
1.6
0.3
20
+
0.7
10
1.2
0.4
20
+
0.6
10
0.6
Source: quoted in Tyrtikov (1964).
Figure 8.13. Diagram illustrating how terrain disturbance of ice-rich soil can lead to thermokarst
subsidence. From Mackay (1970).
trampled and destroyed the tundra vegetation of that area. Within two years, the site had
subsided like a pie dish by a depth of 18-23 cm and the active layer thickness had increased
by more than 10 cm within the depression. Figure 8.13 illustrates how the removal of the
surface organic layer from an area underlain by ice-rich permafrost (composed of 50%
excess ice (water) and 50% saturated soil if it were to thaw) will lead to both ground sub-
sidence and thickening of the active layer.
The ice-rich zone in the transient layer at the top of permafrost (see Chapter 5) is the
fi rst to be affected. Typically, an irregular hummocky relief, similar to baydjarakhii or
 
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