— Why are there weird clumps of frost on otherwise smooth ice?
We discussed this at some length, and the best theory we came up with is that two things are combining here. The first is that the crystals in the lake ice here grew horizontally. Frost growing on top will tend to be aligned with those crystals, and because they're horizontal that doesn't work out. The second might be that once a frost crystal grows in the relatively still air, it will tend to pull water molecules out of the air before they can reach the ice surrounding it. This is similar to how certain rocks grow extraordinarily large crystals when there is a process to inhibit crystal nucleation.
Other theories welcome!
EDIT: A FaceBook commenter noted that when ice is thin and much warmer than the surrounding air, that can lead to sublimation, which will destroy tiny frost, and feed the big ones that protrude well above the ice. I think this is a very plausible explanation for what we saw here.
