Geology Reference
In-Depth Information
Table 10.7. Wind speed and directional data, recorded as a percentage of total time, for the
coastal areas of the Northern Foothills, Southern Victoria Land, Antarctica, by the PNRA.
Wind direction
NNW
NW
WNW
W
WSW
SW
Inexpressible Island
-
14.8
53.2
11.5
2.5
2.7
Terra Nova station
3.3
4.4
17.1
18.0
10.5
8.9
Priestley Glacier
49.3
31.1
2.3
-
-
-
Wind speed (knots)*
1-6
7-16
17-27
28-40
>
41
Inexpressible Island
12.7
18.3
23.2
24.9
18.6
Terra Nova station
50.4
19.0
14.1
8.9
4.4
Priestley Glacier
9.4
15.2
23.2
29.8
21.5
Source: Baroni (1996).
* 1 knot
=
1.85 km/h.
localized weathering effects, niveo-eolian deposits, and certain patterned ground pheno-
mena (Bird, 1967, pp. 237-241; Pissart, 1966a; Washburn, 1969). In some areas, large
Late-Pleistocene sand deposits occur and dune formation is a locally-dynamic process
(Dijkmans and Koster, 1990; Dijkmans et al., 1986; Hamilton et al., 1988). Likewise, on
the Qinghai-Xizang (Tibet) Plateau, dune formation is associated with areas of sand
weathered from weakly-lithifi ed sandstone bedrock (Wang and French, 1995c). In many
tundra regions, as on central Banks Island, Arctic Canada, eolian process are active on
alluvial and outwash plains adjacent to the large rivers (Pissart et al., 1977) and wherever
Mesozoic- and Tertiary-age sandstone and shale bedrock is subject to defl ation. Numerous
other examples could be cited in which wind action has an important direct, but local,
impact.
The indirect effects of wind are more subtle, but possibly more important. For example,
wind plays a primary role in snow redistribution, and infl uences, therefore, slopewash and
runoff processes. Wind also transports sediment, often in combination with snow, to form
niveo-eolian deposits, and may entrain silt and fi ne-sand size particles and redeposit them
over large areas as a thin veneer of what is loosely termed cover-sand. Wind also affects
evaporation and latent heat loss from exposed slopes, which, in turn, infl uences the depth
of the active layer and the magnitude of mass-wasting processes. Asymmetrical valleys
(see above) and the oriented nature of many thaw lakes (see Chapter 8) are further exam-
ples of the indirect effect of the wind. Finally, wind is important to the movement of sea
ice and in wave generation (see below). It is clear, therefore, that wind operates in a
number of indirect ways to infl uence landforms.
10.3.1. Wind Abrasion
If wind is to carry out signifi cant erosion, there must be a source of abrasive material
suitable for wind transportation. Silt and fi ne-sand particles, picked up from exposed
ground surfaces, are one source. Thus, the vegetation-free polar deserts of high latitudes
are especially suited to wind abrasion. However, the ease of detachment of surface parti-
cles may quickly become limited by the formation of a lag composed of coarser particles.
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