b. Photo taken in late January 1970 looking south (U.S. Navy for U.S. Geological Survey). Note airstrips
of Outer Williams Field located just outside the zone of accumulation.
Figure 12 (cont'd). Airphotos of transition between zones of accumulation and ablation.
the transition zone varies from local patches near
Observations and snow depth measurements
the ablation region to over a meter where it phases
over a two-year period in the region where
into the accumulation zone. The Pegasus runway
Pegasus was eventually sited, combined with
was sited just to the accumulation side of where
study of what little is written about Outer Will-
the snow cover ceases to be patchy (Fig. 12c).
iams Field, which existed in the mid-1960s
It has an average natural snow cover of about
(Huffman 1983, Paige 1968), and a review of
0.3 m.
historical airphotos suggested the presence of a
Ablation in the region to the west of Pegasus is
near-constant snow cover averaging about 0.5 m
also a function of the dirt plume that extends
(Mellor and Swithinbank 1989) (Fig. 12a and 12b).
from Black Island. The plume thins (lower vol-
The Pegasus site is situated in a "transition zone"
ume of mineral particles) as it nears the Pegasus
that lies between regions of accumulation and
runway and the melt pool density decreases.
ablation (Swithinbank 1970). The snow cover in
12
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