How do waterfalls freeze while in motion?
In: Chemistry
The same way icicles form. A drop of ice forms. Another drop of water runs along the ice until it freezes.
Moving water can freeze. Once it gets to 32 degrees any nucleation site (a solid touching the water) will cause it to crystalize.
They freeze slowly, so one layer will freeze and then another until they’re all frozen. A bit like the videos where the supercooled water freezes when poured over ice.
It’s because of the no-slip condition. In a stream of moving fluid, there will be a very thin layer of fluid that has zero velocity relative to the solid boundary, and that is where the freezing occurs. When the water passes to a solid, which can be ice or rock in this case. It will slowly freeze, starting from the surface of the solid that the water touches, and then a thin layer of ice is formed, which will then become the next boundary so on and so forth until the whole waterfall is frozen.
Please go to Detectivesp00n’s answer below me for the ELI5 part.
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It has to be very cold, for a long time. Most people know moving water can’t freeze, but in real life scenarios, there’s always a spot where water comes in contact with a solid surface (rocks, ice) that momentarily brings the fluid to a stop, in that short amount of time it has to be cold enough to freeze the water, this spot is called a nucleation spot (where things start). From there it just basically builds outwards, rock to ice and more ice until the whole thing is frozen, the water freezing like a column as it flows down and hits ice below, layer by layer.
Edit: Source: [https://www.reddit.com/r/explainlikeimfive/comments/5mr754/eli5how_do_waterfalls_freeze/](https://www.reddit.com/r/explainlikeimfive/comments/5mr754/eli5how_do_waterfalls_freeze/)
The same reason water freezes while standing still. The average speed of the individual water molecules gradually and uniformly slows down. Eventually, the molecules move so slowly it becomes favored for them to stick together and stop flowing, adopting the properties we know as ice. But I guess you’ll ask “how does something that’s essentially falling slow down midair?”. Let me try to explain…
Instead of seeing ice as an instantaneously halting of atomic motion, imagine a stream of particles whizzing down the waterfall. As they cool down i.e lose energy, they all begin whizzing by at a slower and slower speed on average. Some particles go a little faster, some a little slower, all traveling around the average. Eventually a colder portion of the population slows down so much they freeze. Those water molecules flowing outside or better put ~around~ that population insulates it keeping it ice, alwhile the flow itself becomes colder and colder until it too freezes.
Think of it like a crystaliziation process, growing from inside the coolest part of the waterfall’s stream and outwards. Likewise the process is procedural. At one point, the waterfall 100% liquid. The next, the waterfall is 70% liquid and 30% ice, the liquid portion flowing over a central ice core. Then finally its 99% ice and 1% liquid, with just the faintest trickle of liquid running down the outside, until that too freezes and you get a 100% icefall.
They don’t. They freeze over time.
First the water mist that is deposited on nearby surfaces freezes. Where the water is flowing slowly, droplets can freeze while still attached, and films of water flowing down over the top of those frozen droplets can also freeze, causing icicles. Eventually the river starts to freeze over and form ice dams, which slow down the flow of the river, until the flow even in the middle is slow enough to form these icicles. Eventually there is no flow, and what was a waterfall is all icicles. But this has happened over some time – hours, days, weeks or months.
It just happens to still look something like our normal impression of a flowing waterfall.
I’d concur that they don’t freeze instantly but it’s progressive to the point that no liquid water is present
What’s more interesting is how a wave appears to freeze mid crest. Google frozen waves and look
Well it gets really cold. Past the freezing temp of water. Then it gets colder, to the point where the moving molecules isnt enough to keep it from solidifying. Then… boom frozen waterfall
I’m not an expert in waterfalls, but I think it goes something like this: The waterfall sprays and gets all surfaces wet. The wet surfaces freeze. Rinse, repeat, next thing you know the whole wetness has frozen.
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