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Antarctic conservation

2 Posts tagged with the pressure_ridges tag
1

Under Pressure

Posted by Conservators Sep 20, 2013

Author: Nicola

Date: 18 September 2013

Temperature: -21C

Wind Speed: 15 knots

Sunrise: 7.10

Sunset: 18.30

 

 

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Heading for a walk amoung the pressure ridges © Josiah

 

The pond in the village where I grew up would occasionally freeze over in winter and, with my head filled with images of polar explorers, I always wanted to walk onto its thin, enticing shell of ice.  So, this evening it was a great thrill to be able to step from the land in front of Scott Base and onto the 2m thick sea ice.

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The moon rising above the jagged silhouttes of the broken ice © Nicola

 

I was heading out to explore the extraordinarily beautiful features known as the pressure ridges.  Formed as the ice is squashed up against the land during winter these jagged walls of ice are slowly forced up into strange, distorted, awe-inspiring shapes. As the tide rises puddles of sea water appear around their base then freeze into ponds of blue ice. The shapes are never static, and over the coming months they will gradually change; fracturing, splitting and sagging under their own weight.

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A jumble of fractured sea ice and frozen ponds with Mount Erebus behind © Nicola

 

I carefully followed the safe flagged route, probing the snow in front of me with a pole, checking for new cracks in the ice. In the gloom as the sun went down I was confronted with two massive dark shapes – seals. During the summer hundreds will make their way through the cracks around the pressure ridges and come up for air. I left them peacefully relaxing on the ice and headed back to the base.

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Seals lying on the ice amoung the pressure ridge walk © Nicola

0

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.

 

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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.

 

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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.

 

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