and creates a "badlands"-like topography (Fig.
deposits (Fig. 15) and may indicate how frequently
17). This trend is apparently quite stable; the ef-
storms or events transporting mineral particles
fect of the dirt plume on the snow road was re-
could be expected. If snow is present at the site,
ported in the 1960s when Outer Williams Field
there may be bands of mineral dust stratified in
operated.
the snowpack as evidence of wind-blown con-
Layers of mineral particles are apparent in con-
tamination (Fig. 16). Small amounts of dirt can
centrated bands at several levels within the ice of
lead to serious runway maintenance problems in
the runway. Since these bands are at some depth
a given season.
in the ice and the ice shelf is moving, they repre-
Mineral contaminants periodically invade the
sent contamination events that occurred at an up-
Pegasus site via strong winds. Aerial inspection
stream location. Dirty layers can also be seen in
of the site suggests that Black Island is the source
the snow and were prevalent in parts of the top-
and that strong winds from a south-southwest
most layers of ice that were graded during con-
direction are responsible for their transport. In its
struction of the runway. In addition, during the
current position, the Pegasus runway experiences
past three years while working at the site we
minimal impact from dirt storms. Both ground,
have witnessed mineral particles migrating
air, and core surveys in the area suggest that the
runway is ideally situated with regard to mini-
through the site during storms. At these times,
mizing contamination from this source. From ar-
sand was transported across the snow surface via
eal observation in December, large plumes of dark
saltation and particles often concentrated and were
trapped by small but sharp surface features in
mineral particles can be seen to cover much of the
the snow (Fig. 18).
snow up to just short of the runway. A longer
plume extends past the south end of the runway
and detrimentally affects a 2-km section of the
Flight plate
Prevailing wind direction is the most impor-
snow road from Williams Field about 2 km east of
tant aspect of runway alignment for most airport
the Pegasus site. In December and January the
planners. Most localities with historical meteoro-
snow surface in this area differentially ablates
Figure 17. Rotted snow surface resulting from differential ablation brought on by localized concentra-
tions of mineral particles deposited by wind.
17
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