Water well below freezing point.

[AeroEngy]

I was recently in the interior of Alaska and drove past a flowing river(the Tanana I think) and some small streams( ~5ft wide). The outside temperature was approx -30 F (-34C) not factoring wind chill and had been sub zero for an extended period of time. I know that sediment/contaminants can effect the freezing point and that the fact that the water in motion can be <32 F. However, I was still amazed that at >60°F below freezing that water would still be flowing. Does anyone know if there is some kind of equation that can determine water's freezing point in a turbulent state with sediment? It would have been interesting to stick a thermometer in there to see what the actual water temp was but the fear of falling in and freezing to death in less than a minute dissuaded me.

 

[Ipno]

As I understand it, pure water's freezing point at 1 atmosphere is always 0C but the turbulence in the water creates friction keeping the water above that point.

The sediment would change it depending on what the sediment was, obviously. Here is a nifty calculator to work it out for salt:

Ocean Water Freezing Point Calculator

 

[BrownTown]

The problem in your argument is that you assume the temperature of the water is the same as the temperature of the air, this is not true.

 

[OSX]

This is also assuming that wind chill affects water, which IIRC, it doesn't.

 

[Xdreamer]

i think this is called freezing point depression. its when a water is not pure its freezing point drops. the more junk in the water the more the freezing point drops.
in addtion water under pressure requires additional energy to freeze. so at each point in the stream the water is under pressure from the water behind it .

 

[AeroEngy]

Originally posted by: BrownTown
The problem in your argument is that you assume the temperature of the water is the same as the temperature of the air, this is not true.

I realize that the temperature of the water is not that of air and this is not an argument just a first hand observation.

However, it was just striking/unexpected to see water in its liquid state in the open atmosphere when the air temperature was 60°F below the freezing point(it actually hit -42°F one day). Not to mention that it had been <0°F or at least <32°F for probably a month or more.

I can almost understand the larger river not being frozen just from the mass of water/amount of energy that would have to be removed for it to freeze. But the small stream just doesn't make any since to me. I will post a pic of it when I get home from work. At those temps my general thought would be that it wouldn't take long for a small body of water to freeze over completely but that wasn't the case.

Originally posted by: OSX
This is also assuming that wind chill affects water, which IIRC, it doesn't.

That is why I listed actual temperatures not including wind chill in my original post.

 

[JHutch]

Something else is going on. Either you are mistaken about how long the temperature had been that cold (ie, the water hadn't cooled down enough to freeze yet) or there was a heat source upstream raising the water temp (a natural spring source?).

I've seen huge waterfalls completely frozen in MUCH less hostile temperatures while riding snowmobiles in Michigan. And you don't get much more turbulent than the base of a waterfall.

JHutch

 

[blahblah99]

Water with impurities don't have the same properties as pure H2O.

Add some salt to water, for example, and you have a lower melting point.

 

[marulee]

..turbulence in the water from higher to lower, but melting should be opposite despite atmosphere for its freezing point.

 

[AeroEngy]

Originally posted by: JHutch
Something else is going on. Either you are mistaken about how long the temperature had been that cold (ie, the water hadn't cooled down enough to freeze yet) or there was a heat source upstream raising the water temp (a natural spring source?).

I've seen huge waterfalls completely frozen in MUCH less hostile temperatures while riding snowmobiles in Michigan. And you don't get much more turbulent than the base of a waterfall.

JHutch

I don't think I am mistaken about how long it has been below freezing. According to www.weatheunderground.com the last time the daily high was above +32F was Oct. 28th. I was there from late December until very recently and the temp was sub zero the entire time. Jan 9th was the coldest day at -42F. Heat source upstream is possible I guess but I don't know. See Pics. Also, I did see some guys ice climbing a frozen waterfall in another location. Looked kind of fun but dangerous and to cold for my tastes

River
Smaller Stream

 

[AeroEngy]

Originally posted by: blahblah99
Water with impurities don't have the same properties as pure H2O.

Add some salt to water, for example, and you have a lower melting point.

Yes impurities and salt will lower freezing point. However, sea water still freezes at +28F. The temps where I was was significantly colder than that. The water might have had a warm source such as natural spring. But I must have followed it for 100-150 miles or so along the highway and it was flowing (at least is some capacity) the entire way.

 

[PlasmaBomb]

Yes it is called freezing point depression. If I recall correctly you can get down to about -13*C (8.6*F) with concentrated salt solutions. Wiki

 

[dkozloski]

There are many streams and rivers here in Alaska that flow with open water throughout the winter. Where the water is shallow and turbulent the slightly warmer water mixes with the surface water and keeps it from freezing. Streams that freeze clear to the bottom will backup and flow out over the top and freeze another layer. In stretches of the Tanana River that are deep and steadily flowing the ice can be as much as five feet thick. There are ducks that winter in Fairbanks in open water in the river that flows through town. Here the open water is the result of warm water intruduced to the river from a coal burning powerplant.

 

[BrownTown]

Originally posted by: PlasmaBomb
Yes it is called freezing point depression. If I recall correctly you can get down to about -13*C (8.6*F) with concentrated salt solutions. Wiki

Thats true, but I dont that is the prime reason behind this phenomenon, the concentration of impurities has to be absurdly high to depress the freezing point so far, and its unlikely the water is anywhere near that salty. Sea water only freezes a few degrees below pure water, and it is very very salty.

 

[DrPizza]

Where's the water coming from? Source of the water? It takes a lot of energy loss for water to go from liquid to solid.

 

[AeroEngy]

Originally posted by: DrPizza
Where's the water coming from? Source of the water? It takes a lot of energy loss for water to go from liquid to solid.

As far as I could tell the water is coming from the mountains in what I think is the Alaskan range. I went as far south as Paxson, AK from Fairbanks (about 200 miles). I followed the Tanana River upstream from Fairbanks for 100 miles along Richarsons Highway. It was flowing the entire way. Then Richardsons highway then follows what I think is the Delta River into the mountains for another 100 miles or so (also flowing). There were also various small streams that cross the road appearing to originate from higher elevations in the mountains. These typically flowed in some fashion down from the mountain in small draws.

It does take a lot of energy to change the state of water. But I would think the Heat transfer rate from 32°F water to -30°F air would be pretty high. The only thing that makes any sense to me is that the turbulence of the water somehow generates enough friction/heat to keep it right at the freezing point. Transforming some of the kinetic energy of the flow to thermal energy through friction.

Anyway, this was just an interesting sight on my trip that I did not expect to see and thought I would share.

 

[dkozloski]

What you see flowing in the Tanana River in the summer time is less than 10% of the river. The total flow also includes a huge amount of ground water. This ground water flows into the riverbed all winter bringing with it the heat from the earth. The source of the Tanana is east along the Alaska Highway near the Canadian border. The Big Delta river is just a very small tributary. It's an inch deep and a mile wide.

 

[AeroEngy]

Originally posted by: dkozloski
What you see flowing in the Tanana River in the summer time is less than 10% of the river. The total flow also includes a huge amount of ground water. This ground water flows into the riverbed all winter bringing with it the heat from the earth. The source of the Tanana is east along the Alaska Highway near the Canadian border. The Big Delta river is just a very small tributary. It's an inch deep and a mile wide.

Seems like you have a good understanding of the region. Do you live in Alaska? If so kudos to you. I don't think I could do hack the winter. Way to cold and not nearly enough day light. I would like to come back in the summer to do some more exploring though because it is beautiful up there.


- Just looked up your profile and saw you were in Fairbanks.

 

[dkozloski]

It's pretty nice today. http://arcticcam.com/cam/

 

[Xdreamer]

perhaps it is not water

 

[dfuze]

Are there any underground hot springs or "volcanic" vents that could be nearby to keep the water warm?

It does seem rather odd that something in Alaska could flow like that while the Connecticut River here can freeze over, .... er, just not this winter, where we had 70°F about 2 weeks ago.

 

[dkozloski]

There are hot springs but none in play here. Just a lot of fast moving, turbulent water. Where the river is slower moving it freezes over to ice thicknesses of as much as five or six feet.

 

[Paperdoc]

It's not from freezing point depression - as others said, it takes huge amounts of solutes in the water to depress the freezing point by 10 C degrees, and your temps are 'way to cold for that explanation. It also is not frictional heating from turbulent flow. That does not happen. If it did, water downstream from rapids would always be hotter than upstream, and you are talking HUGE temp difference. All of this is because there is a large flow of water down the stream from sources which are marginally warmer than 0C (32F), and the water simply is not losing heat rapidly enough to all freeze. Some of it does - I'm sure there was some ice along the edges. But most flows downstream before it gets cold enough. And don't forget, once it is down to 0C, there is a lot of heat to be removed (called the heat of fusion) just to get water liquid at 0C to transform into water solid (aka ice) at the same 0C. If you had been able to measure the water temperature accurately, I'd bet it would have been a fraction of a degree (maybe a whole degree) above 0C despite the air temperature.

 

[dkozloski]

Very well put. Also there is a tremendous amount of heat being transferred to the water from the surrounding earth. In winter as well as summer, well water comes from the ground at a temperature of about 36 to 38deg. F. As the water moves downstream in the riverbed, water flows in from the surrounding earth to replace it bringing heat along.

 

[Ipno]

It also is not frictional heating from turbulent flow. That does not happen.

Rapids and water turbulence do create frictional heat. This is part of how Frazil ice forms.