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Ice and Snow Formations

Posted by Conservators Jun 3, 2011

Date: 02/06/2011

 

Posted by Julie

 

Temperature: -22

Wind Speed: Gusting between 20 – 40 knots
Temp with wind chill: - 36  to  -41
Sunrise: August
Sunset August

 

 

Ever since the spectacular ice breakout in February, the ice forming over the water in front of Scott Base has steadily been growing thicker.  Last week the ice was judged thick enough to walk on. Troy, our base leader, Jane, and I set out to mark a safe route for walking through some nearby pressure ridges.

 

Troy is an experienced glacier guide, and so we got the bonus of getting Troy to talk about the snow and ice.  In a crack in the ice we discovered some spectacular, large, faceted ice crystals.  This is sometimes known as crevasse hoar. Troy explained that these ice crystals form and grow in glacial crevasses and in other cavities where a large cooled space is formed and in which water vapor can accumulate under calm, still conditions with a large temperature gradient. The vapour then attaches itself straight to the ice crystal forming a hollow hexagonal shape.

 

faceted ice crystal.jpg

Faceted ice crystal. © AHT/Julie

We also found impressively large icicles.  Icicles require liquid water and so they are notable: the temperature rarely goes above freezing, and certainly has not been above 0 degrees for many months now.

 

Jane as a radioactive rhino.jpg

Jane impersonating a radioactive rhinoceros by shining her headlamp through an icicle. © AHT/Julie


Most spectacular are the pressure ridges themselves.  Pressure ridges form because even very thick sheets of sea ice are mobile. As the sea underneath moves, or when the temperatures fluctuate, the ice shrinks and expands, cracks and shifts.  At Scott Base, the sea ice is bordered by Ross Island on one side and the permanent, immobile ice shelf (80 km thick) on the other.  The relatively thin sea ice between has nowhere to move except upwards, and so plates of ice are very slowly pushed up vertically along cracks, eventually developing into spectacular ice formations. These pressure ridges survived the recent sea ice breakout in February, meaning they are at least 14 years old, the date of the last ice breakout.

 

Pressure ridges.jpg
Pressure ridges.  The formation in the foreground is approximately 5 meters high. © AHT/Julie

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Emergency Conservation

Posted by Conservators Jun 3, 2011

Posted by Martin

 

Date: 01.06.2011
Temperature: -17 degree C
Wind Speed: 40 knots
Temp with wind chill: -48 degree C
Sunrise: n/a
Sunset n/a

 

Sarah mentioned earlier that the explorers in the Heroic Area were very skilled in fixing things and being creative with the limited supplies they had. See this image of Mears making dog harnesses.


Not wanting to be outdone, Julie responded promptly to an urgent conservation task of a slightly different kind. I had been outside for a while in about minus 30degree C and was very happy to get back into the warm base. Pulling off headlight, hat and frozen neck gaiter, I threw off my glasses as well and heard them landing with a sickening noise on the concrete floor. A resin frame at that temperature becomes very brittle which means I could see the fuzzy contours of my glasses separated from the lens. Julie however, in true Antarctic spirit wasn’t fazed and after 24 hours in her care, my glasses almost looked like new.


Photo 2  Martin's glasses under repair.JPG

Martin’s glasses under repair © AHT/Martin


P.S. I just heard that Julie has moved on to fixing the mouthpiece of a saxophone for Victoria, our multi talented base musician.