Part One: Global Overview and Outlook
Introduction to glaciers and ice caps
Glaciers and ice caps form around the world where snow New Zealand and Norway are examples of this type of
deposited during the cold/humid season does not en- glacier (Figure 6B.2). The lower parts of such temperate
tirely melt during warm/dry times. This seasonal snow glaciers may extend into forested valleys, where summer
gradually becomes denser and transforms into peren- warmth and winter snow accumulation prevent develop-
nial firn (rounded, well-bonded snow that is older than ment of permafrost.
one year) and finally, after the air passages connecting
the grains are closed off, into ice
2
. The ice from such
accumulation areas then flows under the influence of
Temperature (°C)
its own weight and the local slopes down to lower alti-
tudes, where it melts again (ablation areas). Accumula-
cold firn
tion and ablation areas are separated by an equilibrium
line, where the balance between gain and loss in the ice
Continuous
permafrost
mass is exactly zero. Where glaciers form thus depends -8
not only on air temperature and precipitation (see Fig- temperate firn
s
ure 6B.1), but also on the terrain, which determines how g
l
a
c
i
e
r
much solar radiation the glacier will receive and where
ice and snow will accumulate.
l
i
n
e
e
q
u
il
ib
r
i
u
m

l
i
n
e

o
n

Discontinuous
t
im
b
e
r
permafrost
In humid-maritime climates the equilibrium line is at a
-1
relatively low altitude because, for ablation to take place,
warm temperatures and long melting seasons are need-
ed to melt the thick layers of snow that accumulate each
2000 500 Precipitation
year
3,4
. These landscapes are thus dominated by ‘temper- (mm)
ate’ glaciers with firn and ice at melting temperatures.
Figure 6B.1: Schematic diagram of glacier, permafrost and for-
Temperate glaciers have a relatively rapid flow, exhibit
est limits as a function of mean annual air temperature and
a high mass turnover and react strongly to atmospheric
average annual precipitation. Forests verge on glaciers in hu-
warming by enhanced melt and runoff. The ice caps mid-maritime climates and grow above permafrost in dry-con-
and valley glaciers of Patagonia and Iceland, the west-
tinental areas.
ern Cordillera of North America, and the mountains of Source: Based on Shumsky 1964
3
and Haeberli and Burn 2002
4
CHAPTER 6B GLACIERS AND ICE CAPS 117
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