Dear Allen and Cryolisters,
Thanks for sharing an interesting case.
I had an impression that it's a similar phenomenon by surface tension,
something like these I found on YouTube:
...though I haven't figured out what makes the surface tension of the water
weaker around the finger for the case of glacier water ...
Before finding these videos, I found an educational material below,
unfortunately in Japanese only:
They put some explanation there.
Here is a translation by Translated with www.DeepL.com/Translator (free version):
1. if you put a little detergent solution in the center of the pepper powder spread on the surface of the water, the pepper will instantly turn into a doughnut shape. This is a good place to start. When sugar water is poured over the surface of the pepper, the donut-shaped pepper will try to return to its original shape. The surface tension of the water will pull the pepper powder out of the water and it will spread. Comparing the surface tension of water and kitchen detergent, the surface tension of kitchen detergent is weaker, so you can see that the kitchen When the detergent is applied, the pepper dust is attracted towards the water, which has a higher surface tension.
2. Also, sugar water has a stronger surface tension than water, so when the sugar water falls to the surface of the water, the surface tension is stronger and the pepper dust tries to return to its original state.
best,
Tetsuo
-----
Tetsuo SUEYOSHI, Ph.D (sueyoshi.tetsuo@nipr.ac.jp)National Institute of Polar Research (NIPR)
10-3 Midori-cho, Tachikawa-city, 190-8518 Japan
Phone: +81.42.512.0913, Fax: +81.42.528.3149
2020年7月11日(土) 2:33 Allen Pope <apope00@gmail.com>:
_______________________________________________Hey Cryolist,Friday afternoon type of question for you. A Physics professor friend of mine is asking me about a phenomenon she calls "glacier stars" and I have to admit it's not something I've ever seen or heard of.To describe: in a melt pool near the toe of the glacier (in this case, Matanuska, but has also been seen at Skaftafellsjökull) with a whole lot of (whitish) suspended sediment, and a surface layer of black particulates. When you touch it with your hand, it does what you see in the video -- the surface layer pulls rapidly away from the touch point, and the edge soon fractures to make the starlike pattern. (But poking with rocks and sticks doesn't cause this to happen.)Here's a short video of the phenomenon: https://www.dropbox.com/s/hqntv99a2foqofe/Glacier-Stars.MOV?dl=0Apparently it's been part of the glacier tour at the Matanuska for decades, but according to my friend, no one knows what's actually happening. In muddier/denser regions, there is more of a cracking phenomenon, rather than the starburst.From my friend: "The black surface layer isn't a spill, though we're also not quite sure what it is. It's some kind of dark particulates, seemingly adsorbed to the air-water interface, that come with the glacier meltwater from spring through when things start freezing again. Preliminary elemental analysis suggests there's a lot of carbon content. But it's not clear if it's coming somehow from the atmosphere or getting scraped up. I'd love to figure out where it's coming from. It's consistent, though -- at the Matanuska they say they've seen it every year since the mid-90s at least. We have some hypotheses about a few possible mechanisms, the strongest (so far) being a surface tension instability (Marangoni effect). We're also considering the possibility that it's lipids spreading and displacing the particle layer, or a charge screening effect caused from the introduction of salts to pure(ish) meltwater."So, Cryolist - does anybody have an explanation for exactly what is happening? Or know how common this is? Or have any other information about this phenomenon?Thanks!Allen
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