I was watching the coverage of the ice sheet that is about to break off Antarctica on CNN, and I could not believe how straight and clean the walls of the different sheets pieces?) looked. The anchor even commented how they looked like they were carved.
What makes the walls of the sheets so straight? Is the ice salty?
Here are some pictures:
The one in the back-middle looks like a perfect square.
Most ice exists as a crystalline solid. It likes to break along its crystal planes.
This NOAA page claims new sea ice has a salinity of up to 10 parts per thousand, dropping to 1-3 parts per thousand in old ice. That’s condsiderably less salty than the polar seas, which run at about 30-35 parts for thousand salt.
That may be true at a microscopic scale, but I don’t think an ice sheet is a single crystal.
But the individual crystals aren’t randomly oriented in sea ice:
So the micro structure gets carried into larger scales. Of course, if you look into the link, you’ll see that the failure mechanisms of ice are actually much more complicated than the previous sentence implies.
Here’s an aerial photo.
It’s also worth noting that protrusions are likely to fall victim to collisions and that the collisions are more likely to be glancing in an ice sheet that is breaking up (partly due to the lack of space to build perpendicular velocity).
Rubbing relatively flat surfaces together is a time honored way of making both flatter (Telescope makers use lapping to generate uniform curved surfaces, but they are careful about the technique used to generate that desired effect).
There is a lot of scraped off debris between those tall sheets.
