Geoscience Reference
In-Depth Information
3.2.3 Snow Cover
In most lakes the ice is covered with snow, which differs from ice layers in many respects
(Fig.
3.9
). Observations and classi
cation of snow on lake ice can be made following the
methods in Fierz et al. (2009). Granberg (1998) has written a review of snow on sea ice,
serving lake ice research as well. The snow cover has a major role in the physics of lake
ice. The structure and properties of snow undergo evolution in metamorphic processes
during the whole ice season. Snow on lake ice has two particular characteristics. First,
since the ice is
floating, the lower part of snow may become slush as shown in Sect.
3.2.2
.
Second, the presence of water at the freezing point temperature beneath the ice provides
heat to cold snow and, consequently, in
fl
uences snow metamorphosis. In particular, in
cold conditions depth hoar may form in the lower snow layer.
In dry climate regions, the snow cover may be missing or is very thin, and, conse-
quently, is rather a minor factor. Such areas are found, for example, in Tibet, Northeast
China, and dry valleys of Antarctica. In very cold climate the adhesion between ice and
snow is weak, and winds are able to clear the snow away if the snow accumulation keeps
on a moderate level or less. This is the normal situation in Lake Baikal.
The basic properties of snow on lake ice are the thickness, density, grain size and
shape, liquid water content, and impurities (Table
3.4
). The density of seasonal snow
ranges from 100 kg m
−
3
for new, loose snow to 400 kg m
−
3
for wind-packed tundra snow,
while the grain size is within 1
fl
10 mm. The liquid water content has a very large
variability, from zero for cold snow to 50 % (volume) for water-soaked snow or slush and
can be more for melting snow. The water holding capacity of snow is about 5 % (DeWalle
and Rango 2008), and due to the relatively large particle (snow crystal) size, the hydraulic
conductivity is good so that the water exceeding the holding capacity is
-
filtrated down
through the snow layer fast.
(a)
(b)
Fig. 3.9
a
Schematic picture of snow on lake ice cover;
b
snow fieldwork on lake ice
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