CHAPTER 7. FUTURE CONSIDERATIONS
ably not significantly reduce the risk associated
LIMITS TO LIFE EXPECTANCY
with calving.
No runway is expected to last forever, even in
the temperate world. Natural processes are con-
Concentration of contaminants
stantly working to erode any runway and its sup-
Contaminants are an unavoidable part of oper-
port facilities. Although maintenance activities are
ating an airport. Both aircraft and maintenance
performed largely to counter these forces, several
vehicles will introduce fuel, lubricants, and cool-
threats may be insurmountable in the case of a
ants to the area. Generally, these are in small,
glacial ice runway. In addition to melt pool for-
dispersed quantities, but in parking areas they
mation, which has been discussed earlier and in
may accumulate to the point where they can act
Lang and Blaisdell (1995), the following issues
as a significant magnet for solar warm-up. These
could be of concern.
types of contaminants tend to migrate downward
leaving a rotted, weak surface and creating sub-
surface cavities.
Glacier movement
The most obvious limit to the long-term viabil-
The soot produced by aircraft when operating
ity of a glacial ice runway is movement of the
on the runway is especially insidious. Mineral
glacier on which the runway is sited. In some
particles can also be an especially troublesome
cases, glacial movement can be very significant,
contaminant. Over time, these deposits will accu-
whereas in others the movement is so slow as to
mulate to become layers that will increase the
be a non-issue. During data gathering in the ini-
potential for surface melt at locations like the Pe-
tial phases of siting such runway, the speed and
gasus site. Maintenance of a thin, removable snow
direction of glacier movement will have been de-
"wearing surface" is about the only defense
termined.
against soot buildup. Disposal of this contami-
Glacial movement could carry a runway into a
nated snow must be to an area that can tolerate
region of ablation and melting, or into an accu-
melting.
mulation zone. Either case would probably result
A plan to deliberately "migrate" the runway
in an ever increasing amount of maintenance re-
can lessen pressure on any given area. In this
quired to operate the runway. At some point it
scheme, perhaps 150 m (500 ft) of runway can be
would be too expensive or time consuming, and
added to one end and 150 m (500 ft) abandoned at
the runway would need to be abandoned. Move-
the other at regular intervals (depending on
ment could also push the runway into an area
amount of traffic and buildup of contaminants).
where crevassing and cracking were prevalent,
At Pegasus, this scheme could be very attractive,
perhaps where the glacier travels over a bedrock
with runway extension occurring southward (up-
bump, or where it expands upon exiting a neck.
stream relative to glacier movement) and aban-
Yet another threat from movement could be the
donment of a segment of the northern end where
proximity to nearby topographic high points. This
operational activities are concentrated (fueling,
could eventually impinge on the normal and ac-
landing, takeoff, parking, cargo, and passenger
ceptable glide slope of aircraft landings and take-
loading/unloading).
offs. By then the runway will likely need to be
In an area where free water occurs during the
relocated for other reasons.
peak of summer, water flowing on the surface
At the Pegasus site, none of the above threats
may move toward the runway, since, after con-
are of concern. The site is near the ice shelf edge,
struction, it will likely present a local depression.
and it is certain that the shelf will eventually calve
Short- and long-term measures can be initiated to
and take all or part of the runway out to sea.
deflect water away from the runway. Infrequent
Although the rate of shelf movement toward the
occurrences of water on the runway, either from
north and the change in elevation is known, it is
water flowing to the site, or from surface or sub-
not possible to estimate when a calving event
surface melting, may not be devastating. While it
could affect the Pegasus runway. Periodic exten-
may interrupt air operations, free water could be
sion of this runway to the south (by perhaps 150
encouraged to freeze in place by saturating it with
300 m, or 5001000 ft) would act to counter natural
snow and ice or draining it away from the run-
glacial movement northward, but would prob-
way with shallow trenches.
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