Pancake ice

It forms as a result of wave action on slush or ice rind.

[1] Pancake ice features elevated rims formed by piling of frazil ice or slush onto the edges of pancakes when they collide, both due to random bumping into each other and because of periodic compressions at wave troughs.

[2] Pancake ice forms in conditions of high wave activity, in contrast to other types of sea ice formed under calm conditions.

[3] If the waves are strong enough, pancakes can raft over each other, creating an uneven top and bottom surface on the ice.

This process increases pancake ice's resilience, resulting in characteristic length scales less than ocean wavelengths and causing waves passing through pancake ice not to scatter.