Figure 55. Horizontal and vertical thin sections of core sample removed from the Pegasus runway surface at the 6000-ft zone

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ticularly in areas where former blisters (domed

in the ice structure.

ice with radial surface cracks) were located. En-

Thin sections of the ice cores were taken from

countering a blister, the grader blade often caught

the north threshold (0-ft), and at the 6000-ft and

the radial cracks and caused them to propagate.

10,000-ft areas of the runway. The cores at 6000-ft

On its own, the grading process probably intro-

and 5000-ft locations were macroscopically simi-

duced new near-surface cracks as well.

lar in structure. A complete profile of the core

We conclude that the following factors contrib-

from the 6000-ft location is shown in Figure 55.

uted to the brittle failures witnessed in the Pe-

Clearly this ice was formed by flooding with snow-

gasus runway ice:

melt water during runway construction. The top

Large grain size ice in areas where the natu-

of the core is characterized by 2- to 3-mm (0.08- to

ral glacial ice had experienced melting and

0.12-in.) diameter, randomly oriented ice grains

refreezing.

included in 8- to 35-mm- (0.3- to 1.4-in.-) equiaxed

a. 0- to 5-cm horizon.

b. 5- to 18-cm horizon.

Figure 55. Horizontal and vertical thin sections of core sample removed from the Pegasus runway surface at the 6000-ft

zone.