Yet More Ice on Minihaha Creek

19 February 2024

After a long unusually warm period, we’ve had a brief period of cold and snow. The creek is still flowing free in most parts, and ice is mostly opaque white granular frozen shelves that protrude from either bank. However, there are areas where recrystallization has occurred, often, though not exclusively, under bridges, and often, though not always, showing signs of melting/refreezing.

Here we can see melting refreezing, with the fine-structure of the crystals erased, and only the large acicular macro-crystals visible.

Something else that interests me is that many of the masses of crystal, both refrozen and ‘fresh,’ have lots of empty space in them. You can see that a little in the image on the upper left; it is more visible in the photo just below. In a book I’m reading, Above the Trees, about the alpine tundra environment, it describes how sheets of ice form across the tops of small depressions, which then act as miniature greenhouses, warming the air below them. I wonder if heat rising from the flowing water is likewise trapped by the panes of ice above them, forming these honeycomb patterns of ice and air.

Sheets of ice, and the acicular crystals, often seem to me at an angle to the surface of the water of about 10-15°. On possibility is that the water in the deeper part of the creek is warmer, and so that there is a temperature gradient that affects the level at which ice crystals grow over the water. I think, but am not certain, the the ice crystals on either bank of the creek angle away from the water as they project out over the stream.

‘honeycomb’ of acicular crystals and plates

Finally, although much of the ice is refrozen, there appear to be areas of fresh crystals, or at least crystals that still show fine structure on the surface. One of the images below (right) is from under a bridge, where I would expect it to be cooler and sheltered from the sun, but the other (left) is from a more normally exposed area of the creek.

mat of acicular crystals with fine structure

The image shown on the left is particularly interesting because it retains a lot of fine structure — etchings and dendrites — on the crystals. More detail below.

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More Ice Crystals on Minihaha Creek

5 February 2024

We continue to have above freezing weather during the day, dipping below the freezing point at night. The leads to a lot of melting and re-freezing on the creek. There are areas where the creek is entirely frozen over, and others where it runs free, except for a fringe along its edges. The ice itself is quite varied. Some is clear, some an opaque white; some has a dull granular texture, some is a palimpsest of crystals upon cyrstals

Ice on Minihaha Creek, 2

11 January 2024

I returned to Minihaha Creek five days after my previous visit for a run, and a look at the ice. The snow, not very deep before, has receded, and the fallen leaves arch above its surface, leaving a myriad of little cave-lets speckling the surface. I wonder if there are any organisms — macro or micro — that are adapted to take advantage of these niches.

First Ice Crystals on Minihaha Creek, 2024

5 January 2024

We’ve had a remarkably long fall. Although we’ve had some chilly periods, the temperatures are still tending to edge above freezing during the day, and in the last month we’ve had days that make it into the forties, and even the fifties. We’ve had two light snows: one but a dusting, and the second perhaps an inch, enough to almost bury the downed leaves. So the world is mostly gray and brown: the dully gray winter sky arches overhead, and the grass, trees, and carpet of leaves is brown brown brown. Very dull.

I have been waiting, with anticipation, for the first ice crystals to form on Minihaha creek, where I do most of my runs. I enjoy looking at ice on the creek as the winter progresses. First, most of the water is open, and a crystalline fringe forms along the edges of still portions of the creek. Next, the fringes grow, meeting in a delicate and parlous surface in the middle. As the cold deepens, the ice thickens. In the early part of the winter the ice tends to be crystal clear — although depending on the way in which the crystals form the may make portions of the surface matte white.

March 1 and Slush Season

Wednesday, 1 March 2023

Happy March 1st! There are now some cracks in the shroud of winter. Oftentimes, it seems to me, there is a period of a few days, usually in February, where the birds suddenly become more active. It is perhaps the first real hint of spring — real, in contrast to the phantom spring thaw that often happens in late January.

Ice Crystals on Minihaha Creek

Saturday, 18 February 2023

The winter here has been weird – a couple of sub-zero weeks, a couple of warmish (32ish) weeks, repeat. I run several days a week, mostly along Minihaha Creek, which winds through south Minneapolis. With the variations in temperature there is a lot of thawing and refreezing, and that, combined with changing water levels in the creek, results in marvelous ice crystals. Mostly they are two dimension intergrowths of needle-like crystals, almost fabric-like in their structure.

Snow Crenellations

Saturday, 17 December 2022

I observed a curious phenomenon on my run today. I have been unable to find an authoritative account or name for it, so I will call them snow crenellations.

Freeze/Thaw and Ice Algae

Tuesday 15 March 2022

There should be a name for this season. It warms, and things melt during the day, and then it refreezes at night. The lake is still iced over, but during the day clear pools of water mirror the sky; yet some people still venture boldly onto the ice – I hope they know what they’re doing.

Ice Algae