c. Looking north taken in December 1989 showing the initial Pegasus runway and areas of patchy snow
to the west. The final Pegasus runway position is located just inside the accumulation zone about 150 m
to the east of the airstrip seen here and about 2 km to the east of the former Outer Williams Field.
Figure 12 (cont'd).
defining the transition zone (Blaisdell et al. 1995,
Trend of accumulation/
Fig. 13). Runway placement was based on the
ablation transition
eastern limit of essentially contiguous snow cover
In some cases, an ideal location for a glacial ice
in late December (Fig. 14). Since the runway at
runway is in the transition between accumulation
Pegasus was specified to be a minimum of 3050 m
and ablation zones. The transition region is usu-
(10,000 ft), the obvious choice for runway align-
ally marked by a constant-depth snow cover. Of-
ment was more or less parallel with the glacio-
ten the transition zone is quite wide and it will
logical zones boundaries. To do otherwise would
have a directional trend. It may also shift slightly
create a condition where each end of the runway
back and forth with variations in climatic condi-
would have very different maintenance needs.
tions in any given year. The width and direction
Fortunately, this choice of alignment coincided
of the transition should be noted. These will have
to be compared with the other site characteristics,
favorably with other factors (e.g., direction of most
common destinations and strong wind direction).
such as distance from obstacles and prevailing
wind direction, to assist in choosing an exact lo-
cation for the runway.
Snow drifting
Indications of wind-driven snow movement at
At the Pegasus site, the transition zone is iden-
the Pegasus site include sastrugi on snow sur-
tified as a band about 2 km wide running ap-
faces and small patches of snow stuck to an other-
proximately north-south. Its western extent is
wise bare ice surface. At the site, the sastrugi are
about 0.5 km east of the abandoned Constellation
aligned in several directions. However, their long
aircraft (named Pegasus and for which our site
dimension is most often aligned with approxi-
derived its name). The Pegasus runway is located
mately 10 true. By contrast, the fuselage of the
approximately in the middle of the transition zone
Constellation aircraft Pegasus, which is aligned
and is aligned roughly parallel to the borders
13
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