Bubbles and Crystals
It’s 6°F out this morning, yes, 6 degrees! Let’s go for a walk around the pond. Bundle up, remember, ‘there’s no bad weather, only bad clothing.’ (That’s usually attributed as a Norwegian saying.) Really, come see this, it’s cool!
From a distance you can see dots on the pond ice, getting closer you can see they are bubbles stacked like snowmen running deep into the ice layers. These bubbles have a story that goes back to the summer months, from moose to bacteria. Hang with me, science ahead!
The pond is an active place in the summer with minnows, turtles, swimming snakes, salamanders, sculpins, snails, dragonflies, water skimmers, ducks, algae growth, and many other players. The algae bloom is normally kept in check when the moose show up, they slurp up all that algae, and the pond water is quite clear. This year, we only saw our pond cleaning technician, Bruce the Moose, once. So, the algae bloom largely stayed in place, but it wasn’t scummy and we opted not to chemically treat it. Moving into Fall, add in leaves, pine needles, dead insects, and other organic matter which have accumulated and sunk to the bottom of the pond. Bacteria feast on it all to break down this organic material and keep nutrients in the pond for next summer’s busy season, which is essential for the health of all life that depends on the pond. This decay process does put off methane gas, think of it as bacteria farts. The methane gets trapped in the ice forming bubbles. As the cold holds on longer, the ice gets thicker and the next layers of bubbles are trapped in the ice.
Some of these bubbles are simply air pockets. They form near the creek inlet which burbles into the pond all the time mixing water and air, a more humid spot. The water flowing into the pond does not freeze over, but close by water vapor does freeze into clear ice or white droplets consisting of many vaporized air molecules to make it white.
Etched patterns form over the water surface as well, fanning out in jagged, but fractally consistent formations. These form much like the frost on your car or house windows where water vapor comes in contact with the already frozen surface. Water is H2O, right? So, it will always form a ‘V’ shape. The two hydrogen atoms attach like Mickey Mouse ears to the oxygen at a 105° angle, so you see this angle played out in the two-dimensional frost patterns on glass or thinner ice. This repeated pattern forms a ‘fractal’, (a consistent repeating pattern from molecular to galaxy-sized). The length and degree of freeze time and other elements factored, like direct sunlight or dirt particles, will affect the extent of the pattern created.
Now, look around the edge of the pond, down by your feet, fuzzy ice crystal growth called Hoar Frost is clinging to grasses and bridge boards. A step back and this hoar frost looks like Einstein’s hair, the word does derive from Old English meaning ‘old person’ or ‘white hair’. Zoom in now and the crystal detail emerges. Here, the crystals are free to form in three dimensions in the pocket of frozen air surrounding the grasses. Frozen water crystals will attach themselves to the nearest surface. In the spaces between the slats of our low boardwalks, water vapor rises and freezes to the boards. Again, the size of the crystal formation depends on the depth of the cold and the length of time it remains. This makes a particularly cold morning an excellent time to step out and see what has formed overnight.
As the sun rose, the ambient air warmed in a few hours to above freezing. Walk back out and you will see the hoar frost will be little rounded ice nubs or simply gone. The next deeply cold night this process will return again, a bit different formation each time.
As for the pond ice, that is here to stay until April. The bubbly ice will soon cover over with layers of snow and animal tracks. This next week is promising to be very cold. I will keep checking on the pond to see what is new.
Sources :
- Ice crystals. (2022, September 15). In Wikipedia. https://en.wikipedia.org/wiki/Ice_crystals
- https://education.nationalgeographic.org/resource/frost
- Frost. (2022, November 7). In Wikipedia. https://en.wikipedia.org/wiki/Frost#Hoar_frost
- https://epod.usra.edu/blog/2021/01/methane-bubbles-frozen-in-an-alaskan-march.html
- https://seagrant.umn.edu/news-information/directors-column/lake-river-ice-formation-classification
- https://www.schlitzaudubon.org/2018/12/24/the-art-and-science-of-ice-formations/
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