f. 63.5- to 68.5-cm horizon.
e. 49.5- to 63.5-cm horizon.
Figure 55 (cont'd). Horizontal and vertical thin sections of core sample removed from the Pegasus runway surface at the
6000-ft zone.
ented (Fig. 57). This ice also appears to be firn.
less than 0.5 to 9 mm (0.02 to 0.35 in.) (Fig. 56).
Above this depth, the ice seemed to be meltwater-
This uppermost layer appears to be firn. In the
derived but the ice was too damaged to construct
horizon section at approximately 32 to 34 cm (12.5
a thin section.
to 13 in.) the ice grain size increases and this
The gap seen in some cores was also evident at
increase is relatively linear up to a depth of 81 to
the bottom of the failure zones. The thin gap (0.5
86.5 cm (32 to 34 in.). The ice grains are more
1.5 cm, or 0.20.6 in.) had an unknown, but lim-
uniform and the average grain size ranges from 5
ited, areal extent. Hoar crystals were usually
to 10 mm (0.2 to 0.4 in.). The origin of this ice also
present in this gap. The gap is speculated to result
appears to be glacial, but distinctly older as crys-
from either coalescing of trapped air bubbles at
tals have coalesced to form larger grains. Thin
the water/ice interface during freeze-up of water
sections were not constructed between 10.5 and
from the prior season, or from heaving of the
81 cm (4 and 32 in.); these specimens were pre-
upper ice layer when it expands during freeze-up
served for shipment to CRREL and compressive
causing arching (Klokov and Diemand 1995). In
strength testing.
some cases when the gap was present, it was
At the north end (0 ft) the core between 10.3-
located at a depth of 2536 cm (1014 in.) from the
and 20.5-cm (4- and 8-in.) depth shows grain sizes
ice surface, while in others it was observed at a
from less than 0.5 up to 5 mm (0.02 to 0.2 in.) in
depth of 75 cm (30 in.) or more. This gap obvi-
diameter and they appear to be somewhat ori-
54
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