One of my favourite phenomena right now is desublimition, or deposition: The phase transition of water vapour to ice that doesn’t go through the liquid phase. It happens when moist air is cooled below the dew point and condensation doesn’t occur spontaneously: When the supercooled water vapour then gets in touch with a cold surface, it turns to ice immediately. And the results are incredibly beautiful!
These pictures are all from a trip I took with my godson and his family to Möhne Reservoir, the largest artificial lake in western Germany. You can see we were actually on a shore: What a surreal mixture of shells, leaves and frost flowers.
And we initially just wanted to go over and have a look at the fog that we saw across the Reservoir from where we were throwing stones in the water…
Getting closer, we were almost afraid that we’d encounter dementors there. We could feel it getting a lot colder, and there was frost on the shore and ice on the water… Spooky :-)
Frost flowers! I learned about those in the context of Arctic and Antarctic ice formation. I kinda assumed that ice flowers only formed in salt water, because I remember hearing about how the ice needles that form wick up brine and that, due to their large surface (which you will remember noticing in the last post where we looked at them forming on trees), they are super important in the air-sea exchange of all kinds of stuff, like for example bromine. So imagine my excitement when I saw them growing the other day!
Frozen Schlei river in Schleswig
Frost flowers are really pretty by themselves, but they also tell us a lot about recent weather conditions. For example, they only form when the air is A LOT colder than the water/ice surface. Do you know the snowy ice crystals you sometimes find on the inside of ice cream containers when you’ve opened and refrozen them? Yep – same thing! I even suspect that the ice crystals I was talking about in this post are also frost flowers.
Frost flowers
I find it really fascinating how they are distributed over the larger surface of the Schlei river.
Schlei river in Schleswig coated in frost flowers
Here, for example, you see them forming on the edges of ice that has been broken up by some mechanical process. Judging from their placement, I would suspect that they only formed after the ice was broken and some of the pieces tilted up.
Cracked ice and frost flowers
Here, they were probably everywhere, but then the ice got broken up and some parts submerged. When the water there refroze, no snow flowers formed, just “normal” ice. However, the existing snow flowers seem to have continued growing!
Ice with frost flowers. Partially submerged and then refrozen into “normal” ice
The really interesting thing is that frost flowers don’t actually form from the water that is freezing below, but from water vapour in the air. Which, btw, explains why they can form on benches, ice cream lids or trees (all of which would be really difficult if they could only form on open water surfaces).
Ice with frost flowers. Partially submerged and then refrozen into “normal” ice
Above you see a larger part of the Schlei’s surface: Seems like there used to be frost flowers everywhere, but when the ice broke up, some of it got pushed out of the water, and as such preserving the frost flowers and letting them continue to grow. Meanwhile, other parts got flooded and only normal ice formed there. Maybe because the temperature gradient at that point wasn’t large enough any more?
Isn’t this just beautiful??? I could watch this all day, every day.
Frozen Schlei river in Schleswig with frost flowers
But let’s look at some more details. No idea why that patch of frost flowers formed there! But they seem to always start in small patches, which eventually grow together if the conditions are stable enough over long enough periods of time.
Frost flowers on ice
Here, we see the opposite situation to the one a couple of pictures up: “Normal” ice had formed, and then was broken up. And then, when the crack froze over, frost flowers formed!
What happens when water vapour freezes to ice without going through the liquid phase? Frost flowers!!!
That’s when trees suddenly look like this:
Frosted tree.
Btw – the stem of that tree is painted white! That’s just to confuse you a little but…
But let’s take a closer look. This is what the branches look like: Tiny ice needles growing on the individual pine needles! And the orientation of the image below is correct. They are growing to the side!
Frosted tree.
You can clearly see them all growing to one direction, to one side!
Frosted tree.
When you take off a bit of frost, this is what it looks like. Needles, but with a fractal 3D structure! Since what happened here (water vapour freezing without becoming liquid in between) is basically snow forming on the surfaces down here instead of in the clouds up above, it isn’t too surprising that snow is exactly what the frost bits feel like.
A piece of frosting. This picture isn’t blurry – the ice needles have a fractal 3D structure!
Look below, you can clearly see the frost only growing to one side (and this picture is the right way up, too!):
Frosting on tree branches
Doesn’t it make you want to sit there and just watch?
What a nice picknick spot!
Although every time the slightest of breezes comes, this is what happens:
Tree being de-frosted by wind
Also really cool: These plants growing on a balcony behind a glass railing. Only the tips have been frosted!
Plants on balcony with frosted tips
And if you were wondering what this post has to do with oceanography, check out the image below. Can you spot it?
Frozen Schlei river in Schleswig
Can you spot it now? No, not my niece (although she is pretty cool, too!), the frost flowers!
