Geoscience Reference
In-Depth Information
(a)
Figure 15.5
Sections through permafrost;
(a) north-south section
through principal zones from
North West Territories to
northern Alberta, Canada;
(b) formation of interstitial and
segregated ice lenses by
downward migration of the
freezing plane. Note that
migration of water to the
freezing plane leaves a
desiccation layer.
75°N
55°N
Sporadic
Continuous
Discontinuous
0
0
10
100
200
300
400
Permafrost table
500
Permafrost
Talik
Active layer
600
(b)
Sub-zero air temperature
Lens 1
T
1
FP
1
Lens 2
2a
FP
2
T
2
Lens 3
T
3
FP
3
Interstitial
ice
Segregated
ice
Water
migration
Dessicated
layer
Non-frozen
layer
Thermodynamic characteristic
Cold polar glaciers
Temperate alpine glaciers
Input (accumulation) and output (ablation)
Low, 10
4-6
cm
3
m
-2
a
-1
High, 10
6-7
cm
3
m
-2
a
-1
Mass storage
High, 10
6-7
km
3
Low, 10
1-2
km
3
Energy flux to melt accumulation at ELA
Low, 10
0-1
kcal m
2
a
-1
High, 10
1-3
kcal m
2
a
-1
Annual mass turnover
Low, 0.001-0.01% a
-1
High, 1-5% a
-1
Thermal regime
Polythermal
Isothermal
Basal regime
Cold, frozen
Warm, unfrozen
Principal flow mechanism
Internal deformation
Basal sliding
Secondary flow mechanism
Basal sliding
Internal deformation
Flow velocity
Low, 10
1-2
m a
-1
High, 10
2-3
m a
-1
Area above ELA
Large, approx. 80-90%
Moderate, approx. 40-60%
Area/thickness configuration
Tabular
Columnar
Channel type
Unconfined
Confined
Land area glacierized
Large, 80-100%
Small-moderate, 10-50%
System stability
Highly stable-metastable
Unstable-highly unstable
Note: These are general values for glaciers operating in steady state with standard behaviour.
