Expedition Diary January 7, 2008
3500 meters above sea level
Maximum & Minimum temperatures: - 24 to - 35 °C
Never a uniform white blanket on the ice sheet, the character of the surface snow takes on many different forms. On the microscale, different crystal forms tell stories of their arrival to the surface as gently falling snow, wind-battered hard pack, or deposition as surface hoar through condensation events.
To a traverse train of vehicles, generous amounts of gently-fallen snow represent “snow swamps” in which the treads sink and dig their way in, sometimes preventing a vehicle from pulling its sled. Thick and hard wind-pack is a driver’s dream, allowing the vehicle and its sleds to easily pass.
Surface hoar is not even noticeable to the vehicle or its driver. Winds on the ice sheet blow surface snow around, eroding it from some places and re-depositing it in others, resulting in larger-scale surface roughness forms called sastrugi that, even though they may be hard-packed, can slow or halt vehicles if they grow to sufficient size.
In this part of the continent there are large fields of “megadunes”, roughness features several meters high and several kilometers in wavelength reminiscent of ocean swells. On the leading faces of these dunes are meter-high sastrugi made of snow so wind-packed that a pick-axe can barely penetrate. Sastrugi like that would prevent vehicle passage. Long before departure, we made maps, using satellite images, that trace a route designed to avoid the large sastrugi areas of megadune fields that would slow our headway. Today we easily slipped around several such fields, intrigued by their presence out to the side of the vehicles, but also relieved that we could avoid direct encounters.
Image caption: Mary standing beside a typical sastruga encountered on this traverse, and standing beside a sastruga in a megadune field in 2004 (Photos: Mary Albert).
This contribution is from the log of the Norwegian-US Scientific Traverse team, who are en route from Troll Station to South Pole Station. Much more information can be found here.
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Wednesday, 09 January 2008 00:46
Scales of roughnessWritten by US-Norway Traverse
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