Built on either snow or ice, the life spans and limitations of McMurdo Station's three runways are largely determined by the type of ice on which they are built, the amount of snow that drifts or falls on them, and the degree to which the heat penetrates the surfaces. In mid-August, a few Winfly flights land on Pegasus Ice runway with crews that build the sea ice runway, the main airfield from October to December. |
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On the sea ice, the saltwater freezes in a manner that segregates the salt into brine pockets, which melt first and make potholes. Because exposure to the sun weakens the ice, during sea ice operations, crews are careful to keep a thin layer of snow on the ice in an effort to reflect the sun's harmful rays. Too much snow is bad because it acts as an insulator early in the season from cold air temperatures, which drive ice thickness growth. Later, thick snow traps heat, which melts the ice. During the weeks leading to December, while the temperature is getting warmer, the ice is getting thicker. At about five months, the lag time in which the sea responds to temperature change is much slower than the air's quick response. By mid-summer, the sea ice is 8 to 10 feet thick, but the warm sun has usually damaged the surface with soft spots. Under snowy Williams Field, the ice is covered by so much snow - at least 25 feet - that it is not considered an ice runway. The integrity of the ice's surface is not an issue here. While Pegasus is closed, mid-November to late January, management pays close attention to protecting the ice runway from the sun by covering it with a blanket of snow. Fleet operators try to maintain about a 7-inch snow layer. The mid-season snow-spread is too fluffy and loose to support wheeled
plane landings. Each January, the operators strip the snow layer, leaving
the ice bare, on which wheeled planes can land. The goal is to open Pegasus to wheeled C-130 aircraft immediately after the sea ice runway closes. - Beth Minneci |