Frost flowers on ice cream. You must have seen them before: They sometimes occur when you’ve had some ice cream, put the left-overs back in the freezer, and take them out again. And there you have it: Water-ice crystals all over your lovely ice cream! Completely annoying because, obviously, they only taste like water and mess up your whole ice cream experience (or is that only me)?
Frost occurs when water vapour freezes without going through the liquid phase. Look at the awesome crystals!
Once I started thinking about the process that formed the ice and realised that those were actually frost and not just ordinary ice crystals, they all of a sudden stopped being annoying and instead became something that I kinda look forward to finding when I open a tub of my frozen blended strawberries. Because the structures are different every time, and really really pretty! And also how awesome is it to know that those ice crystals formed from water that wasn’t even liquid? Yes, this is the kind of stuff that makes me happy! :-)
Using the “melting ice cube” experiment to let future instructors experience inquiry-based learning.
I recently (well, last year, but you know…) got the chance to fill in for a colleague and teach part of a workshop that prepares teaching staff for using inquiry-based learning in their own teaching. My part was to bring in an experiment and have the future instructors experience inquiry-based learning first hand.
So obviously I brought the ice cubes melting in fresh water and salt water experiment! (Check out that post to read my write-up of many different ways this experiment can be used, and what people can learn doing it). On that occasion the most interesting thing for me was that when we talked about why one could use this — or a similar — experiment in teaching, people mainly focussed on the group aspect of doing this experiment: How people had to work together in a team, agree to use the same language and notation (writing “density of water at temperature zero degree Celsius” in some short syntax is not easy when you are not an oceanographer!).
And this experiment never fails to deliver:
you can be 100% sure that at least in one group, someone will say “oh wait, which was the salt water again?” which hands you on a plate the opportunity to say “see — this is a great experiment to use when talking about why we need to write good documentation already while we are doing the experiment!”
you can also be 100% sure that in that group, someone will taste the water to make sure they know which cup contains the salt water. Which lets you say your “see — perfect experiment to talk about lab safety stuff! Never ever put things in your mouth in a lab!”
you can also be sure, that people come up with new experiments they want to try. At EMSEA14, people asked what would happen if the ice cubes were at the bottom of the beaker. Today, people asked what the dye would do if there was no ice in the cups, just salt water and fresh water. Perfect opportunity to say “try! Then you’ll know! And btw — isn’t this experiment perfect to inspire the spirit of research (or however you would say that in English – “Forschergeist” is what I mean!). This is what you see in the pictures in this blog post.
So yeah. Still one of my favorite experiments, and I LOVE watching people discover the fascination of a little water, ice, salt and food dye :-)
Photo taken by Ulrike Bulmann
Photo taken by Ulrike Bulmann
Btw, when I gave a workshop on active learning last week and mentioned this experiment, people got really really hooked, too, so I’ll leave you with a drawing that I liked:
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.
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:
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!
You can clearly see them all growing to one direction, to one side!
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!
For most of my readers it might be pretty obvious what the movement of floating ice says about the flow field “below”, but most “normal” people would probably not even notice that there is something to see. So I want to present a couple of pictures and observations today to help you talk to the people around you and maybe get them interested in observing the world around them more closely (or at least the water-covered parts of the world around them ;-)).
For example, we see exactly where the pillars of the bridge I was standing on are located in the river, just by looking at the ice:
What exactly is happening at those pillars can be seen even more clearly when looking at a different one below. You see the ice piling up on the upstream side of the pillar, and the wake in the lee. Some smaller ice floes get caught in the return flow just behind the pillar. Now imagine the same thing for a larger pillar – that’s exactly what we saw above!
And then we can also see that we are dealing with a tidal river. Looking at the direction of the current only helps half of the time only, and only if we know something about the geography to know which way the river is supposed to be going.
But look at the picture below: There we see sheets of ice propped up the rails where the rails meet the ice, and more sheets of ice all over the shore line. As the water level drops due to tides, newly formed ice falls dry and that’s all the sheets of ice you see on land.
The bigger ice floes in the picture have likely come in from the main arm of the Elbe river.
Small port on a tiny bay on the Elbe river in Hamburg. Look at the sheets of ice on shore!
It is actually pretty cool to watch the recirculation that goes on in all those small bays (movie below picture). Wouldn’t you assume that they are pretty sheltered from the general flow?
My friend Elin is currently on a research cruise in Antarctica and you really need to check out her blog. She is writing about life at sea, including the most beautiful photos of sea ice. Today’s post is called “ice or no ice” and describes the first couple of days of the research cruise. Elin combines the catching narrative with exercises and experiments that will be conducted by at least 30 schools all over Norway! And maybe you can use some of her posts, exercises and experiments in your teaching, too?
Today, for example, the exercises are all about ice. Depending on how much brain power you want to invest and how much prior knowledge your students have, you could for example do an exercise about Archimedes’ principle, calculating how much of an ice floe is visible above the water’s surface, and how many scientists you could put on it before people start getting wet feet. Or, more challenging, you could work with real data that Elin provides to practice your statistics and look at the annual cycle of sea ice in Antarctica. Or you could even set up differential equations for how ice thickness increases over time.
There will be new exercises every Monday for the next two months. How exciting!
Elin’s blog, “På tokt i Antarktis“, is available in English, Norwegian and Swedish. So you can use it not only to practice your maths and physics, but also your language skills! :-)
Btw, if you got hooked and can’t nearly get enough of reading about that research cruise, there is a second blog that tells you, for example, about the different kind of New Year’s Eve the scientists and crew had before heading off to Antarctica. Also very much worth a read!
In my last post, I showed you the legendary overturning experiment. And guess what occurred to me? That there is an even easier way to show the same thing. No gel pads! (BUT! And that is a BIG BUT! Melting of ice cubes in lukewarm water is NOT the process that drives the “real” overturning! For a slightly longer version of this post check this out).
So. Tank full of luke warm water. Red dye on one end. Spoiler alert: This is going to be the “warm” end.
Now. Ice cubes on the “cold” end. For convenience, they have been dyed blue so that the cold melt water is easily identifiable as cold.
A very easy way to get a nice stratification! And as you see in the video below, awesome internal waves on the interface, too.
And because I know you like a “behind the scenes”:
I took this picture sitting on my sofa. The experiment is set up on the tea table. The white background is a “Janosch” calendar from 15 years ago, clipped to the back of a chair. And that is how it is done! :-)
My new favorite thing is to put strawberries through a blender and then freeze small portions of that to eat as ice cream later. It is super yummy plus you never know what you’ll see when you open the lid!
Sometimes, you get long crystals like these:
Ice crystals on strawberry ice cream
And then other times, you get something completely different. Look at those circular shapes! Perhaps that’s where the UFO landed? You can’t really see it in the picture, but those disks come quite a bit higher than the rest of the ice.
Ice crystals on strawberry ice cream
In the bottom left corner, you see a smudge – that is where I pried off one of the disks to see what might have caused it. Turns out there is a cavity underneath. So somehow bubbles in the strawberry mash freeze out into those disks?
I am guessing that the ice cream in the second picture came from a batch that I beat harder than the one in the first picture, hence more bubbles. Or maybe the one in the first picture sat outside the freezer longer, so the bubbles had all reached the surface and popped before it went into the freezer? What do you guys think? Seems like I should really be carefully writing protocols next time I’m making ice cream! :-)
Because surely there is one more post in this topic? ;-)
For those of you who haven’t heard about the “melting ice cube” obsession of mine, please check out the links to other posts at the end of this post. For everybody else’s sake, let’s dive right in!
When Kristin and I ran the workshop at EMSEA14, a couple of people asked very interesting questions. One that I totally had to follow up on was this: What would happen if the ice cubes were forced to the bottom of the beakers? Of course we knew what theory said about this, but who cares? I still had to try.
If you have ever tried holding down ice cubes with straws…
…and we have a movie of this! :-)
…you might know that that is quite difficult. So this is the experimental setup I ended up with:
Ice cubes melting at the bottom of a fresh water and a salt water beaker
Zooming out a little bit, this is my fancy equipment:
The camera gets a white skirt over the tripod because the reflection of the tripod is seriously annoying
Zooming out a little more, this is the whole setup:
Chair on table in my winter garden, holding the white-ish oilcloth that serves as background. I should invest in a proper rod for the upper edge of the oil cloth, the current one has suffered a bit…
I know that some people want to try the experiment for themselves, so I’ll hide the rest of the experiment behind the cut, at least until Kristin tells me that she’s done it :-)
I had to do the complete series of experiments, of course…
The other day I mentioned that I had used salt from my kitchen for the “ice cubes melting in fresh and salt water” experiment, and that that salt was the super healthy one that was both iodized and containing folic acid. And what happened is that the experiment looked like I was using milk. Not what I had envisioned.
Ice cubes melting in fresh water (left) and in iodized-salt-with-folic-acid water (right)
Since I had often before used just regular table salt – which is usually iodized – I was intrigued by the opaqueness that seemed to be due to the addition of folic acid. Or was it? That I had never noticed the milky-ness of the salt water didn’t necessarily mean that it had not been milky before. So this is what the same experiment looks like if regular iodized table salt is used:
Ice cubes melting in fresh water (left) and in iodized-salt water (right). Turbulence in the freshwater beaker due to me stirring (don’t ask)
In the literature it is always recommended to use kosher salt for experiments. Kosher meaning in this context that the salt should be only NaCl with no other additions. I happened to have some at hand after having bought it for the “teaching oceanography” workshop in San Francisco last year (after the salt that I brought for the workshop didn’t make it to the US. Long story). So this is what that looks like:
Ice cubes melting in fresh water (left) and in kosher salt water (right)
In summary: Folic acid is what makes the salt water look opaque – but iodized salt is completely fine for tank experiments. I think it’s tiny air bubbles that cling to something folic acid-y, but I have no clue what is going on. I noticed that the dusty stuff settled down over night (so the top experiment here is a lot clearer than the experiment I ran with the same batch of water the day before), but even the next day the water wasn’t completely clear.
Anyway, now we know. And I came out of this series with more movies of ice cubes melting in fresh water and salt water!
Links to previous posts on the topic after the cut.
[Edit: Using my mom’s iodized, but not folic acid containing, table salt leads to milky water, too. So there you have it. I have no clue what is going on!]