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Wanting to know more about ice formation
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I've been trying my hardest to learn a little more about how ice formation works.. How long does it take for ice to form in the right conditions? Why does some snow melt and form ice during freeze/thaw and some doesn't? Do springs always freeze over in the right conditions? Basically, is there any source for learning a little more about how it all actually works? Kind of a generic question, but any answers are appreciated! |
Sam Root wrote: I don't think that book that Dharma Bum linked will help. Sure, it is an interesting book (though not as good as the one written by Hobbs), but more about the physical properties of ice. Your questions mainly involve heat flow. In general, melting will occur as soon as the ice starts to exceed 0 C, but how rapidly that happens depends on the heat flow to and from the ice. Concerning the rates, the density of the ice will have an effect, and impurities in the meltwater will too. For freezing, the water must go to some temperature below 0 C for pure water, usually at least 3 degrees C, but generally less than 6 C, unless it is in contact with ice, in which the melt will just freeze. But freezing generate heat (the latent heat of fusion), which slows down the rate of freezing and generally raises the meltwater temperature to with a few tenths of a degree below zero. This slows down the freezing rate, and makes it depend on the heat flow, which is highly dependent on the environment. Contrary to widely held beliefs, running meltwater or springwater is unfrozen only because it is too warm, and has nothing to do with its motion. I wish there was a good book about natural ice, but I don't know of any. I have a blog about snow and ice (www.storyofsnow.com), but it doesn't address your questions here. |
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Jon, I really appreciate the reply! It's so crazy how complex ice is.. So I guess another question I might ask is where should you look for ice in the mountains? One thought would be a shaded cliff below a south facing snow slope. What are some of the main places that ice is going to naturally form? Thank so much! |
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Hi Sam, good questions. I haven't spent time looking for large ice formations in the mountains, so really can't help you there. For the refrozen stuff that you seem to be looking for (i.e., not snow or glacial ice), your thought is a good one, though there are so many possible combinations of terrain, season, weather, and latitude, that it may be hard to generalize. Obviously, in the northern hemisphere, northern sides would have ice for longer, but whether or not it is the type you want is hard to say. It would be an interesting topic to study. Good luck- |
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my wife is a physics teacher and used it for part of her class. |
Dharma Bum wrote: that still doesn't make it relevant to the question. here is an article i found helpful when i had similar questions a few days ago: http://www.alpineadven.com/recentandcurrent/iceformation.html |
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Sam, Amazon has a guidebook, 'ice Climbing Utah' on sale for $6.99. Most guides have listed the most reliable climbs. Idaho is a great ice climbing venue. |
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This is a good summary: |
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Petzl has some relevant research as well: https://www.petzl.com/fondation/projets/etude-cascade-de-glace?language=en#.Wil_2nplDqA |
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The art of ice climbing is pretty good, I've got the french version: http://www.blueice.com/en/books/94-the-art-of-ice-climbing.html I  I've also got a study of ice formation which was created to better asses road and highway closures on the north shore of the Saint-Lawrence. |
Jon Nelson wrote: Is temperature not a measure of motion (kinetic energy) at the molecular level? |
W Ham wrote: Disordered motion, not flowing motion. The molecular motion is also vastly faster than the flow, even at 0 C, being hundreds of meters per second. Still water on a pond or edge of a stream can freeze not because it is still, but because it cools more at one spot (the top surface). Of course, being still allows it to cool at the top, instead of mixing with warmer water below. My point is that the flowing motion itself is not preventing freezing, rather, it is the mixing that keeps the water at a uniform (relatively warm) temperature. Anyway, it is just a common misconception I sometimes hear and thought I might try to help clear up. Does it help? Once the water is cold enough and ice forms, flowing motion against the ice will actually speed up the freezing because it increases the heat flow away from the growing ice.
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Radiolab just put out an interesting podcast that spends some time talking about water freezing. It won't help you decide what's good ice or not, but it is an interesting listen. |
Jon Nelson wrote: While I appreciate your trying to explain all this in scientific terms (and you're doing a good job at it, don't get me wrong), I can't let this statement stand. As I'm sure you know, heat only flows from higher T to lower T. And I hope you also realize that water only freezes at a single temperature, namely 0 C or 32 F if you prefer. You can't have liquid ice (at standard pressure) at any lower T nor can you have solid ice at T > 0 C. So if the ice is actively forming, it is at exactly 0 C. And heat would only flow "away from the growing ice" into something at a temp lower than 0 C. So unless the waterfall is vodka or some similar non-aqueous system, it can't be colder than the ice. Most often (not always, but I don't want to start splitting hairs) the ground is warmer than the air, so heat is more typically lost to the air (evaporative cooling and conduction) and that's when the water freezes. If the ground surface temp is < 0 C then that can freeze the water as well, but the only way we get cold ground is from COLDER air. |
Gunkiemike wrote: Thanks Mike. I'm not sure what you mean by "liquid ice", but I suppose you mean meltwater, or just plain old liquid water. As I stated above, meltwater must be "supercooled" below 0 C for ice to initially form. Generally, at least to -3 C. Ice growth then releases heat, which tends to raise the water temperature to close to 0 C, but it cannot reach to exactly 0 C or the ice surface would be in contact with meltwater at 0 C and would stop growing. Using flowing water to speed ice formation is common in the laboratory when one wants to increase the rate of freezing or decrease temperature or solute gradients. This supercooling is essential for all cold-cloud processes. You would get almost no rainfall if you didn't have droplets supercooling to at least -10 C and certainly no thunderstorms (perhaps look up the "cold rain process"). In some clouds, the water drops supercool to nearly -40 C. It's an interesting topic, but none of this is controversial. Folks tried to exploit it for one type of cloud seeding, but due to various complex issues with clouds, I'm not sure if it was ever shown to be reliable. In general, unlike supercooling meltwater, it is hard to superheat ice significantly above 0 C, but it does happen internally. It is necessary for the formation of "Tyndall figures" -- little vapor inclusions in ice exposed to the sun. I'm not sure why you are talking about the ground temperature always being warmer than the air, but these winter days in the Seattle area would be much more boring if the ground didn't cool more than the air. It leads to various types of interesting frost formation. This cooling of the ground is not driven by the air temperature, but to radiative cooling. |
Jon Nelson wrote: If you're positing that the ground reaches temperature lower than the immediately surrounding air, then I see no point in discussing this with you further. Surface frost formation is all about dew point and condensation. And water DOES NOT need to reach -3 C in order to freeze on a surface, be it rock or ice. |
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I read the book and thought it would help the OP to understand the basic principles of ice. No need to be nasty about it. |
