Environmental Engineering Reference
In-Depth Information
bed) to a few tens of metres per year. Low-energy
polar
or
cold glaciers
are
consequently large and stable, capable of surviving relatively large climatic fluctuations.
The Antarctic Ice Sheet and Greenland Ice Cap are the largest modern polar ice bodies
but during Earth's glacial maxima two or more similar ice sheets form over much of
North America and Eurasia.
By contrast, warmer alpine climates experience heavier snowfalls and more rapid
melt. Ice forms quickly and flow velocities are measured in 10
1-3
m a
−1
. However, these
high-energy
alpine
or
temperate glaciers
are much smaller and far more susceptible to
even small climatic changes. They are restricted today to high mountains like the Alps,
Himalayas, Andes and North American cordillera, where they are topographically
constrained within the valleys they have eroded. Thermodynamic character therefore also
determines glacier configuration (Figure 1). Larger and thicker ice sheets are less
constrained spatially but lower average velocity reduces their geomorphic impact except
in the vicinity of
outlet glaciers
, where large ice volumes accelerate towards ice sheet
margins and create the most impressive erosional landforms.
Table 1 Mass balance, iceflow and thermodynamic characteristics of
principal glacier systems
Characteristic
Cold polar glaciers
Temperate alpine glaciers
Low, 10
4-6
cm
3
m
−2
a
−1
High, 10
6-7
cm
3
m
−2
a
−1
Input (accumulation) and output
(ablation)
High, 10
6-7
km
3
Low, 10
1-2
km
3
Mass storage
Low, 10
0-1
kcal m
2
a
−1
High, 10
1-3
kcal m
2
a
−1
Energy flux to melt accumulation at ELA
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.
