I had better explain a bit about sea-ice, so people understand a bit about what we are walking around on. When it gets cold enough (below -1.8 degrees) for long enough, the salt water in the polar regions freezes from the top down. Firstly, "grease ice" appears on the surface (some is visible around the bits of solid ice in the photo above). It is so thin, it actually bends without breaking as waves go past. It looks like a darker or lighter patches on the water, depending on what angle you are on. This then turns to "frazzle ice", with sugary crystals of ice floating on-top of the water. Often as the ice becomes thicker, wind and wave action separate the ice into round flat chunks, called "pancake ice" (see blog entry
here). Finally the whole thing clumps together and freezes solid to form true sea-ice. As he ice becomes thicker, it effectively insulates the water below from the cold air above, and the rate of growth slows. Eventually the growth almost completely stops at around 1.7 to 1.8 metres. According to our AAD field manual, 200mm of ice is OK to walk on,
400mm of ice is OK to drive quads on, and 600mm of ice is OK to drive the tracked vehicles (
Hagglunds) on. The ice we walk over to get out to Gardner Island is called "fast ice" because it is attached fast to land. It is really solid ice, but continually develops cracks at the land/sea interface due to tidal action (tide cracks). Now it is melting (degrading from above) and rotting (degrading from below), care needs to be taken crossing it. You occasionally fall through melted sections to a depth of around 30cm, so it is a good idea to wear water-proof boots! This pic shows some of the melt pools on the surface of the fast ice near Gardner Island.
I had better explain a bit about sea-ice, so people understand a bit about what we are walking around on. When it gets cold enough (below -1.8 degrees) for long enough, the salt water in the polar regions freezes from the top down. Firstly, "grease ice" appears on the surface (some is visible around the bits of solid ice in the photo above). It is so thin, it actually bends without breaking as waves go past. It looks like a darker or lighter patches on the water, depending on what angle you are on. This then turns to "frazzle ice", with sugary crystals of ice floating on-top of the water. Often as the ice becomes thicker, wind and wave action separate the ice into round flat chunks, called "pancake ice" (see blog entry here). Finally the whole thing clumps together and freezes solid to form true sea-ice. As he ice becomes thicker, it effectively insulates the water below from the cold air above, and the rate of growth slows. Eventually the growth almost completely stops at around 1.7 to 1.8 metres. According to our AAD field manual, 200mm of ice is OK to walk on,
400mm of ice is OK to drive quads on, and 600mm of ice is OK to drive the tracked vehicles (Hagglunds) on. The ice we walk over to get out to Gardner Island is called "fast ice" because it is attached fast to land. It is really solid ice, but continually develops cracks at the land/sea interface due to tidal action (tide cracks). Now it is melting (degrading from above) and rotting (degrading from below), care needs to be taken crossing it. You occasionally fall through melted sections to a depth of around 30cm, so it is a good idea to wear water-proof boots! This pic shows some of the melt pools on the surface of the fast ice near Gardner Island.
No comments:
Post a Comment